JP7809293B2 - Video distribution system, video distribution device, terminal device, video distribution method and program - Google Patents

Description

The present invention relates to a video distribution system, a video distribution device, a terminal device, a video distribution method, and a program.

A monitoring system has been proposed that includes multiple network cameras, a log management device that manages logs, and a control console that divides the display screen into three areas: an image content switching area, a content display menu area, and a content display area; displays a list of content that can be displayed in the image content switching area, a list of content display methods in the content display menu area, and displays content in the content display area using the selected content and display method (see, for example, Patent Document 1). In this monitoring system, when the control console receives event information, it highlights the display screen of the image from the relevant network camera.

Japanese Patent Application Laid-Open No. 2005-129999

In a system equipped with multiple network cameras like the one described above, if an abnormality occurs in one of the network cameras, there is a demand for the system to be restored as quickly as possible by making it easier for users to understand the cause of the abnormality.

The present invention was made in consideration of the above, and aims to provide a video distribution system, video distribution device, terminal device, video distribution method, and program that make it easier for users to understand the cause of an abnormality when it occurs.

In order to achieve the above object, the video distribution system according to the present invention comprises:
a link status determination unit that determines a link status with the network camera;
a session determination unit that determines whether a session with the network camera can be established;
an image acquisition unit that acquires image information obtained by compressing an image captured by the network camera using a preset compression encoding method when a link with the network camera and a session are established;
a decoding unit that executes a restoration process to restore the image information;
a restoration determination unit that determines whether the restoration of the image information has been successful as a result of the restoration process;
and an image forming unit that selects a display mode for the display unit based on at least one of the link status, whether the session can be established, and the result of the restoration process, and forms a display image of the selected display mode.

From another viewpoint, the video distribution system according to the present invention is
A video distribution system that distributes image information captured by a network camera to a terminal device via a video distribution device connected to the network camera,
The video distribution device is
a link status determination unit that determines a link status with the network camera;
a session determination unit that determines whether a session with the network camera can be established;
an image acquisition unit that acquires image information obtained by compressing an image captured by the network camera using a preset compression encoding method when a link with the network camera and a session are established;
a decoding unit that executes a restoration process to restore the image information;
a restoration determination unit that determines whether the restoration of the image information has been successful as a result of the restoration process;
and an image forming unit that selects a display mode for the display unit based on at least one of the link status, whether the session can be established, and the result of the restoration process, and forms a display image of the selected display mode.

From another perspective, the video distribution device according to the present invention is
a link status determination unit that determines a link status with the network camera;
a session determination unit that determines whether a session with the network camera can be established;
an image acquisition unit that acquires image information obtained by compressing an image captured by the network camera using a preset compression encoding method when a link with the network camera and a session are established;
an image transmitting unit that transmits the acquired image information to a terminal device;
and a status notification unit that generates status notification information indicating the link status and whether the session can be established and transmits the information to the terminal device.

A terminal device according to another aspect of the present invention comprises:
an image acquisition unit that acquires image information obtained by compressing an image captured by a network camera using a preset compression encoding method;
a status notification acquisition unit that acquires status notification information transmitted from a video distribution device, the status notification information indicating a link status between the network camera and the video distribution device and whether a session can be established between the network camera and the video distribution device;
a decoding unit that executes a restoration process to restore the image information;
a restoration determination unit that determines whether the restoration of the image information has been successful as a result of the restoration process;
and an image forming unit that selects a display mode to be displayed on a display unit based on at least one of the link status and whether the session can be established indicated by the status notification information and the result of the restoration process, and forms a display image of the selected display mode.

From another viewpoint, the video distribution method according to the present invention comprises:
determining a link status between the network camera and the video distribution device;
determining whether a session can be established between the network camera and the video distribution device;
acquiring image information obtained by compressing an image captured by the network camera using a preset compression encoding method when a link and a session between the network camera and the video distribution device are established;
performing a restoration process to restore the image information;
a step of determining whether the image information has been successfully restored as a result of the restoration process;
The method includes a step of selecting a display mode for the display unit based on at least one of the link status, whether the session can be established, and the result of the restoration process, and forming a display image in the selected display mode.

From another viewpoint, the program according to the present invention is
Computer,
a link status determination unit that determines the link status with the network camera;
a session determination unit that determines whether a session with the network camera can be established;
an image acquisition unit that acquires image information obtained by compressing an image captured by the network camera using a preset compression encoding method when a link with the network camera and a session are established;
a decoding unit that executes a restoration process to restore the image information;
a restoration determination unit that determines whether the restoration of the image information has been successful as a result of the restoration process;
an image forming unit that selects a display mode on a display unit based on at least one of the link state, whether the session can be established, and a result of the restoration process, and forms a display image in the selected display mode;
Function as.

According to the present invention, the image forming unit selects the display mode for the display unit based on at least one of the following three factors: the link status with the network camera, whether a session with the network camera can be established, and the results of the restoration process for image information compressed using a preset compression encoding method, and forms a display image in the selected display mode. As a result, if an abnormality occurs in the video distribution system, the display mode of the image displayed on the display unit changes depending on the cause of the abnormality. Therefore, by checking the display mode of the display image, the user can understand the cause of the abnormality and more easily deal with the abnormality.

1 is a diagram showing a configuration of a video distribution system according to a first embodiment of the present invention; 1 is a diagram illustrating a hardware configuration of a video distribution system according to a first embodiment. 1 is a diagram showing a functional configuration of a video distribution system according to a first embodiment; (A) is a diagram showing an example of information stored in a state memory unit provided in a video distribution device related to embodiment 1, and (B) is a diagram showing an example of information stored in a state memory unit provided in a video distribution device related to embodiment 1. FIG. 2 is a sequence diagram showing the operation of the video distribution system according to the first embodiment. 4 is a diagram showing an example of a display image displayed on a display unit of the terminal device according to the first embodiment; FIG. FIG. 2 is a sequence diagram showing the operation of the video distribution system according to the first embodiment. (A) is a figure showing an example of a display image displayed on the display unit of a terminal device when the link with the network camera is cut off, relating to embodiment 1; and (B) is a figure showing an example of a display image displayed on the display unit of a terminal device when a session with the network camera cannot be established, relating to embodiment 1. FIG. 2 is a sequence diagram showing the operation of the video distribution system according to the first embodiment. 10 is a diagram showing an example of a display image displayed on a display unit of a terminal device when a restoration process of image information has failed, according to the first embodiment; FIG. FIG. 2 is a sequence diagram showing the operation of the video distribution system according to the first embodiment. (A) is a figure showing an example of a display image displayed on the display unit of a terminal device when a link with a network camera is interrupted midway through, according to embodiment 1; and (B) is a figure showing an example of a display image displayed on the display unit of a terminal device when a session with a network camera cannot be established midway through, according to embodiment 1. FIG. 2 is a sequence diagram showing the operation of the video distribution system according to the first embodiment. 10 is a diagram showing an example of a display image displayed on a display unit of a terminal device when a restoration process of image information fails midway, according to the first embodiment; FIG. 10 is a flowchart showing an example of the flow of a video distribution process executed by the video distribution device according to the first embodiment. 10 is a flowchart showing an example of the flow of a video display process executed by the terminal device according to the first embodiment. FIG. 10 is a diagram showing a functional configuration of a video distribution system according to a second embodiment of the present invention. FIG. 10 is a sequence diagram showing the operation of the video distribution system according to the second embodiment. FIG. 10 is a sequence diagram showing the operation of the video distribution system according to the second embodiment. 10 is a flowchart showing an example of the flow of a video distribution process executed by a video distribution device according to a second embodiment. 10 is a flowchart showing an example of the flow of a video distribution process executed by a terminal device according to the second embodiment. FIG. 10 is a sequence diagram showing the operation of a video distribution system according to a modified example. FIG. 10 is a diagram showing an example of a display image displayed on a display unit of a terminal device when the restoration process of image information fails midway, according to a modified example.

(Embodiment 1)
A video distribution system according to an embodiment of the present invention will be described in detail below with reference to the drawings. The video distribution system according to this embodiment includes a link status determination unit that determines a link status with a network camera, a session determination unit that determines whether a session with the network camera can be established, and an image acquisition unit that acquires image information in which images captured by the network camera are compressed using a preset compression encoding method when a link with the network camera and a session are established. The video distribution system also includes a decoding unit that performs a restoration process to restore the image information, a restoration determination unit that determines whether the restoration of the image information was successful as a result of the restoration process, and an image formation unit that selects a display mode for the display unit based on at least one of the link status, whether a session can be established, and the result of the restoration process, and forms a display image in the selected display mode. This embodiment will be described in detail below. Note that the image information in the video distribution system according to this embodiment of the present invention may include not only still images but also moving images.

As shown in FIG. 1, the video distribution system 100 according to this embodiment includes four network cameras 2A, 2B, 2C, and 2D (hereinafter also referred to as network cameras 2, etc.), a video distribution device 1 connected to these network cameras 2, etc. via a network NW, and a terminal device 3. The network NW is, for example, a wired local area network (LAN) conforming to the Ethernet standard. The network cameras 2A, 2B, 2C, and 2D are used, for example, as surveillance cameras for monitoring production equipment. As shown in FIG. 2, the network cameras 2A, 2B, 2C, and 2D each include a central processing unit (CPU) 201, a main memory unit 202, an auxiliary memory unit 203, an imaging unit 204, a wired communication interface 206, and a bus 209 connecting the various components. The main memory unit 202 is composed of volatile memory such as random access memory (RAM). The auxiliary storage unit 203 is composed of a nonvolatile memory such as a read-only memory (ROM) and stores programs for controlling the network cameras 2A, 2B, 2C, and 2D. The imaging unit 204 includes, for example, a lens barrel holding at least one lens and an image sensor (neither of which is shown) positioned at the imaging position of at least one lens, and outputs image information representing the captured image. The wired communication interface 206 is connected to the network NW and transmits and receives data via the network NW. The CPU 201 loads and executes programs stored in the auxiliary storage unit 203 into the main storage unit 202, thereby functioning as an encoding unit 211, a connection processing unit 212, and an image transmission unit 213, as shown in FIG. 3. The main storage unit 202 shown in FIG. 2 also includes a compressed image buffer 221, as shown in FIG. 3, which temporarily stores image information obtained by compressing images captured by the imaging unit 204 using a preset compression encoding method. Examples of compression encoding methods include H.261 and H.262 using discrete cosine transform. H.263, H.264, MPEG-1, MPEG-2, MPEG-3, etc. may be used. Alternatively, a compression encoding method using subband coding or wavelet transform may be used.

When the encoding unit 211 receives the image information from the imaging unit 204, it compresses the image information using the compression encoding method described above and stores it in the compressed image buffer 221.

The connection processing unit 212 executes processing to establish a link with the video distribution device 1 and processing to establish a session. Specifically, the connection processing unit 212 acquires an FLP (First Link Plus) burst transmitted from the video distribution device 1, and if the communication speed and communication mode indicated by the FLP burst match those corresponding to the network cameras 2A, 2B, 2C, and 2D, negotiation with the video distribution device 1 is successful and a link is established. Here, the communication mode indicates either full-duplex or half-duplex communication. The connection processing unit 212 also transmits an FLP burst corresponding to the communication speed and communication mode of the network cameras 2A, 2B, 2C, and 2D to the video distribution device 1. Furthermore, after a link is established with the video distribution device 1, the connection processing unit 212 receives connection request (DESCRIBE) information from the video distribution device 1 requesting the transmission of connection information necessary to establish a session with the video distribution device 1. In response, the connection processing unit 212 transmits the requested connection information related to its own device along with response information to the video distribution device 1. Here, the connection information is information that defines the connection method, transmission method, media type, etc., described using, for example, SDP (Session Description Protocol). Next, when the connection processing unit 212 receives communication start (SETUP) information transmitted from the video distribution device 1, it transmits response information in response. Thereafter, when the connection processing unit 212 receives image transmission request (PLAY) information transmitted from the video distribution device 1, it generates response information in response and transmits it to the video distribution device 1.

The image transmission unit 213 transmits the image information stored in the compressed image buffer 221 to the video distribution device 1. Here, the image transmission unit 213 transmits the image information using UDP (User Datagram Protocol), RTP (Real-time Transport Protocol)/RTCP (RTP Control Protocol). Note that in this embodiment, the communication protocols used by the image transmission unit 213 are described using the three communication protocols mentioned above as examples, but are not limited to these. The communication protocol may be any communication protocol that can be used for audio and video data.

Returning to FIG. 2, the video distribution device 1 comprises a CPU 101, a main memory unit 102, an auxiliary memory unit 103, a wired communication interface 106, a wireless module 107, and a bus 109 connecting the various components. The main memory unit 102 is composed of volatile memory such as RAM and is used as a work area for the CPU 101. The auxiliary memory unit 103 is composed of non-volatile memory such as ROM, or an SSD (Solid State Drive), HDD (Hard Disk Drive), etc., and stores programs for controlling the video distribution device 1. The wired communication interface 106 is connected to the network NW and transmits and receives data to and from the network camera 2, etc. via the network NW. The wireless module 107 communicates wirelessly with the terminal device 3 using a communication method that complies with the wireless LAN standard, for example, IEEE 802.11.

By loading and executing the programs stored in the auxiliary memory unit 103 into the main memory unit 102, the CPU 101 functions as a connection processing unit 111, a link status determination unit 112, a session determination unit 113, an image acquisition unit 114, an image transmission unit 115, and a status notification unit 116, as shown in FIG. 3. Also, as shown in FIG. 3, the main memory unit 102 shown in FIG. 2 has a compressed image buffer 121 that temporarily stores image information transmitted from the network cameras 2A, 2B, 2C, and 2D. Furthermore, as shown in FIG. 3, the auxiliary memory unit 103 shown in FIG. 2 has a status memory unit 131 that stores information indicating the link status and whether a session can be established between the network cameras 2A, 2B, 2C, and 2D and the video distribution device 1.

As shown in Figure 4(A), for example, the status storage unit 131 represents information indicating the link status and whether a session can be established between each of the network cameras 2A, 2B, 2C, and 2D and the video distribution device 1 using code numbers starting with F, and stores the information in association with camera information indicating the camera number that identifies the corresponding network cameras 2A, 2B, 2C, and 2D. The example shown in Figure 4(A) indicates that links with network cameras 2A, 2C, and 2D are established (connected), and that the link with network camera 2B is disconnected (disconnected). It also indicates that sessions can be established with network cameras 2A and 2D, but cannot be established with network cameras 2B and 2C.

The connection processing unit 111 executes processing for establishing a link between the network cameras 2A, 2B, 2C, and 2D, and processing for establishing a session. Specifically, the connection processing unit 111 acquires FLP bursts transmitted from each of the network cameras 2A, 2B, 2C, and 2D, and if the communication speed and communication mode match those corresponding to the network cameras, negotiation with the network cameras 2A, 2B, 2C, and 2D is successful, and a link is established. The connection processing unit 111 also transmits FLP bursts corresponding to the communication speed and communication mode of the video distribution device 1 to the network cameras 2A, 2B, 2C, and 2D. The connection processing unit 111 then generates communication start information and transmits it to the network cameras 2A, 2B, 2C, and 2D. Next, upon receiving response information from network cameras 2A, 2B, 2C, and 2D, the connection processing unit 111 transmits image transmission request information to the network cameras 2A, 2B, 2C, and 2D requesting the transmission of images stored in the compressed image buffer 221 of each network camera. After receiving the response information from network cameras 2A, 2B, 2C, and 2D, the connection processing unit 111 begins receiving image information transmitted from network cameras 2A, 2B, 2C, and 2D. Furthermore, when a session release event occurs that triggers the release of a session, the connection processing unit 111 transmits session release request (TEARDOWN) information to network cameras 2A, 2B, 2C, and 2D, thereby releasing the session established with network cameras 2A, 2B, 2C, and 2D.

The link status determination unit 112 determines the link status with each of the network cameras 2A, 2B, 2C, and 2D. Specifically, the link status determination unit 112 determines that a link is established when the communication speed and communication mode corresponding to the network cameras 2A, 2B, 2C, and 2D indicated in the FLP burst acquired by the connection processing unit 111 match the communication speed and communication mode corresponding to the video distribution device 1 and negotiation with the video distribution device 1 is successful. On the other hand, the link status determination unit 112 determines that the link is disconnected when the connection processing unit 111 cannot acquire an FLP burst from the network cameras 2A, 2B, 2C, and 2D, or when the communication speed and communication mode indicated in the FLP burst acquired by the connection processing unit 111 do not match the communication speed and communication mode corresponding to the video distribution device 1 and negotiation with the video distribution device 1 is not successful. The link status determination unit 112 then stores link status information indicating the link status corresponding to each of the network cameras 2A, 2B, 2C, and 2D in the status storage unit 131.

The session determination unit 113 determines whether a session can be established with the network cameras 2A, 2B, 2C, and 2D. When the connection processing unit 111 acquires response information corresponding to communication start information transmitted from the network cameras 2A, 2B, 2C, and 2D, the session determination unit 113 determines that a session can be established if, for example, the network cameras 2A, 2B, 2C, and 2D support RTP based on the acquired response information. On the other hand, when the connection processing unit 111 acquires response information transmitted from the network cameras 2A, 2B, 2C, and 2D, the session determination unit 113 determines that a session cannot be established if, for example, the network cameras 2A, 2B, 2C, and 2D do not support RTP based on the acquired response information. The session determination unit 113 then stores session establishment feasibility information indicating whether a session can be established for each of the network cameras 2A, 2B, 2C, and 2D in the status storage unit 131.

When a link and session are established between the video distribution device 1 and the network cameras 2A, 2B, 2C, and 2D, the image acquisition unit 114 acquires image information transmitted from each of the network cameras 2A, 2B, 2C, and 2D. The image acquisition unit 114 stores the acquired image information in the compressed image buffer 121. Here, the image acquisition unit 114 acquires image information using UDP and RTP/RTCP. Note that in this embodiment, the communication protocols used by the image acquisition unit 114 are described using the three communication protocols mentioned above as examples, but are not limited to these. The communication protocol may be any communication protocol that can be used for audio and video data.

The image transmission unit 115 wirelessly transmits the image information stored in the compressed image buffer 121 to the terminal device 3.

The status notification unit 116 generates status notification information including link status information, session establishment availability information, and camera information stored in the status memory unit 131, and transmits it to the terminal device 3.

Returning to FIG. 2, terminal device 3 is a personal computer capable of wireless communication with video distribution device 1, for example, using a communication method conforming to the IEEE 802.11 wireless LAN standard, and includes a CPU 301, a main memory 302, an auxiliary memory 303, a display 304, a wireless module 307, and a bus 309 connecting the various components. Main memory 302 is composed of volatile memory such as RAM and is used as a work area for CPU 301. Auxiliary memory 303 is composed of non-volatile memory such as ROM, or an SSD, HDD, etc., and stores programs for controlling terminal device 3. Display 304 is, for example, a display device with an LCD display. Wireless module 307 communicates wirelessly with wireless module 107 of video distribution device 1, for example, using a communication method conforming to the IEEE 802.11 wireless LAN standard.

By loading the program stored in the auxiliary memory unit 303 into the main memory unit 302 and executing it, the CPU 301 functions as an image acquisition unit 311, a decoding unit 312, a decoding determination unit 313, a status notification acquisition unit 314, an image formation unit 315, and a display control unit 316, as shown in Figure 3. Also, as shown in Figure 3, the main memory unit 102 shown in Figure 2 has a compressed image buffer 321 that temporarily stores image information transmitted from the video distribution device 1, and a display image storage unit 322 that stores display image information indicating the display image to be displayed on the display unit 304. Furthermore, the auxiliary memory unit 103 shown in Figure 2 has a status storage unit 331 and an image storage unit 332, as shown in Figure 3. As shown in FIG. 4(B), for example, the status storage unit 331 represents information indicating the link status and session establishment status between each of the network cameras 2A, 2B, 2C, and 2D and the video distribution device 1, as well as decode success/failure information indicating whether the image information restoration process was successful, using code numbers starting with F, and stores the information in association with camera information indicating the camera number that identifies the corresponding network cameras 2A, 2B, 2C, and 2D. The example shown in FIG. 4(B) indicates that the restoration process was successful for the image information corresponding to network camera 2A, and that the restoration process failed for the image information corresponding to network camera 2D.

The image storage unit 332 stores image information corresponding to each of the network cameras 2A, 2B, 2C, and 2D obtained by restoring the image information stored in the compressed image buffer 321, in association with the camera information.

When the image acquisition unit 311 acquires image information transmitted from the video distribution device 1, it stores the acquired image information in the compressed image buffer 321.

The decoding unit 312 generates restored image information by performing a restoration process on the image information stored in the compressed image buffer 321, and stores the generated image information in the image storage unit 332 in association with the corresponding camera information.

The decoding determination unit 313 is a restoration determination unit that determines whether the restoration of image information was successful as a result of the restoration process performed by the decoding unit 312. Each time the decoding unit 312 performs the restoration process, the decoding determination unit 313 generates decode success/failure information indicating whether the restoration of image information was successful, updates the decode success/failure information stored in the status storage unit 331, and stores this information in the status storage unit 331 in association with the camera information.

When the status notification acquisition unit 314 acquires status notification information transmitted from the video distribution device 1, it extracts link status information, session establishment availability information, and camera information contained in the acquired status notification information, associates these with each other, and stores them in the status storage unit 331.

The image forming unit 315 appropriately forms display images including images indicated by image information corresponding to each of the network cameras 2A, 2B, 2C, and 2D, for example by split display. In doing so, the image forming unit 315 selects the display mode on the display unit 304 for the image corresponding to each camera based on at least one of the link status information, session establishment success/failure information, and decode success/failure information indicating the results of the restoration process stored in the status memory unit 331, and forms a display image in the selected display mode. Here, the image forming unit 315 forms a display image including images indicated by image information corresponding to each of the network cameras 2A, 2B, 2C, and 2D. The image forming unit 315 stores display image information indicating the formed display image in the display image memory unit 322.

In addition, if the link between the video distribution device 1 and the network cameras 2A, 2B, 2C, and 2D remains disconnected, a session cannot be established, or image information restoration fails immediately after the video distribution device 1 is started, the image forming unit 315 forms a pre-set first abnormality notification image as the display image for the corresponding network camera 2A, 2B, 2C, and 2D. Furthermore, when a link between the video distribution device 1 and the network cameras 2A, 2B, 2C, and 2D is established, a session can be established between the video distribution device 1 and the network cameras 2A, 2B, 2C, and 2D, and image information has been successfully restored, if an abnormality occurs and the state transitions to a state in which the link between the video distribution device 1 and the network cameras 2A, 2B, 2C, and 2D is cut off, a state in which a session cannot be established with the network cameras 2A, 2B, 2C, and 2D, or a state in which image information restoration fails, the image forming unit 315 displays the image indicated by the image information acquired from the network cameras 2A, 2B, 2C, and 2D immediately before the abnormality occurred, while superimposing a predetermined second abnormality notification image different from the above-mentioned first abnormality notification image to notify that an abnormality has occurred, and forms this as the display image for the corresponding network camera 2A, 2B, 2C, and 2D. The image forming unit 315 then forms a display image including an image indicated by the image information corresponding to each of the network cameras 2A, 2B, 2C, and 2D, and the first abnormality notification image or the second abnormality notification image. The image forming unit 315 stores display image information indicating the formed image in the display image storage unit 322.

The display control unit 316 causes the display unit 304 to display the display image indicated by the display image information stored in the display image storage unit 322.

Next, the operation of the video distribution system according to this embodiment will be described with reference to Figures 5 to 14. It is assumed that immediately after power is applied to the video distribution device 1, the link status information, session establishment success/failure information, and decoding success/failure information corresponding to each of the network cameras 2A, 2B, 2C, and 2D stored in the status memory unit 131 of the video distribution device 1 are set to "F10 (not connected)," "F20 (establishment not possible)," and "F30 (failure)," respectively. First, when power is applied to the video distribution device 1, an FLP burst indicating the communication speed and communication mode of the video distribution device 1 is transmitted from the video distribution device 1 to the network cameras 2A, 2B, 2C, and 2D (step S1). Meanwhile, an FLP burst indicating the communication speed and communication mode of the network cameras 2A, 2B, 2C, and 2D is also transmitted from the network cameras 2A, 2B, 2C, and 2D to the video distribution device 1 (step S2). Here, if the communication speed and communication mode indicated in the FLP bursts transmitted from network cameras 2A, 2B, 2C, and 2D match the communication speed and communication mode corresponding to video distribution device 1 and negotiation is successful, video distribution device 1 determines that links with network cameras 2A, 2B, 2C, and 2D have been established (step S3). In this case, video distribution device 1 updates the link status information stored in status storage unit 131 corresponding to each of network cameras 2A, 2B, 2C, and 2D to "F11 (connected)" (step S4).

Next, assume that the aforementioned session establishment event occurs. Here, the session establishment event may be, for example, a display operation on terminal device 3 to display images captured by network cameras 2A, 2B, 2C, and 2D on display unit 304. In this case, transmission command information instructing video distribution device 1 to transmit image information to terminal device 3 is transmitted from terminal device 3 to video distribution device 1 (step S5). In this case, connection information request information is transmitted from video distribution device 1 to network cameras 2A, 2B, 2C, and 2D (step S6). Here, connection information is information defining the connection method, transmission method, media type, etc., described by SDP, for example. Meanwhile, upon receiving the connection information request information, network cameras 2A, 2B, 2C, and 2D transmit the aforementioned connection information to video distribution device 1 in response (step S7). Meanwhile, the video distribution device 1 generates communication start information based on the connection information acquired from the network cameras 2A, 2B, 2C, and 2D (step S8), and the generated communication start information is transmitted from the video distribution device 1 to the network cameras 2A, 2B, 2C, and 2D (step S9). Meanwhile, when the network cameras 2A, 2B, 2C, and 2D acquire the communication start information, response information is transmitted from the network cameras 2A, 2B, 2C, and 2D to the video distribution device 1 in response, and the video distribution device 1 acquires this information (step S10).

Meanwhile, let us assume that the video distribution device 1 determines, based on the acquired response information, that network cameras 2A, 2B, 2C, and 2D support RTP and that session establishment is possible (step S11). In this case, the video distribution device 1 updates the session establishment possibility information stored in the status memory unit 131 for each of network cameras 2A, 2B, 2C, and 2D to "F21 (session establishment possible)" (step S12). Next, the video distribution device 1 generates status notification information including the link status information, session establishment possibility information, and camera information stored in the status memory unit 131 (step S13), and transmits the generated status notification information from the video distribution device 1 to the terminal device 3 (step S14). Meanwhile, upon acquiring the status notification information, the terminal device 3 extracts the link status information, session establishment possibility information, and camera information included in the acquired status notification information. The terminal device 3 then updates the link status information and session establishment availability information corresponding to the camera information stored in the status storage unit 331 with the newly extracted link status information and session establishment availability information (step S15).

Furthermore, the network cameras 2A, 2B, 2C, and 2D capture images using the imaging unit 204, sequentially encode image information representing the captured images using a preset compression encoding method, and store the encoded image information in the compressed image buffer 221 (step S16).

Furthermore, when the video distribution device 1 receives the response information in step S10, it transmits image transmission request information to the network cameras 2A, 2B, 2C, and 2D in response thereto (step S17). Meanwhile, when the network cameras 2A, 2B, 2C, and 2D receive the image transmission request information, it transmits response information to the video distribution device 1 in response thereto (step S18). Thereafter, the network cameras 2A, 2B, 2C, and 2D identify image information to be transmitted to the video distribution device 1 from the image information stored in the compressed image buffer 221 (step S19), and the identified image information is compressed and transmitted from the network cameras 2A, 2B, 2C, and 2D to the video distribution device 1 (step S20). Meanwhile, when the video distribution device 1 receives the compressed image information, it stores the acquired compressed image information in the compressed image buffer 121 (step S21). Next, the compressed image information stored in the compressed image buffer 121 is transmitted from the video distribution device 1 to the terminal device 3 (step S22).

Meanwhile, the terminal device 3 stores the acquired compressed image information in the compressed image buffer 321 (step S23). Next, the terminal device 3 performs a restoration process on the compressed image information stored in the compressed image buffer 321 (step S24). Assume here that the terminal device 3 determines that the restoration of the image information has been successful (step S25). In this case, the terminal device 3 updates the decode success/failure information stored in the status memory unit 331 for each of the network cameras 2A, 2B, 2C, and 2D to "F31 (success)" (step S26). The terminal device 3 then forms a display image including an image indicated by the image information corresponding to each of the network cameras 2A, 2B, 2C, and 2D, and stores display image information indicating the formed display image in the display image memory unit 322 (step S27). Next, the terminal device 3 displays the display image indicated by the display image information stored in the display image memory unit 322 on the display unit 304 (step S28). Here, the terminal device 3 displays on the display unit 304 a display image GA1 in which images GA11, GA12, GA13, and GA14 indicated by image information corresponding to network cameras 2A, 2B, 2C, and 2D, respectively, are arranged two-dimensionally, as shown in FIG. 6, for example.

Also, as shown in FIG. 7, after the video distribution device 1 is powered on and the aforementioned FLP burst is transmitted from the video distribution device 1 to the network cameras 2A, 2B, 2C, and 2D (step S1), it is assumed that, among the network cameras 2A, 2B, 2C, and 2D, the FLP burst cannot be obtained only from camera 2B. In this case, the video distribution device 1 determines that negotiation with network camera 2B has not been established and that the link with network camera 2B has been disconnected (step S29). In this case, the video distribution device 1 leaves the link status information stored in the status memory unit 131 corresponding to the network camera 2B from which the FLP burst could not be obtained set to "F10 (unconnected)," and sets the link status information of the other cameras 2A, 2C, and 2D to "F11 (connected)" (step S30). The video distribution device 1 then generates status notification information including link status information, session establishment availability information, and camera information stored in the status storage unit 131 (step S31), and transmits the generated status notification information from the video distribution device 1 to the terminal device 3 (step S32). Meanwhile, upon acquiring the status notification information, the terminal device 3 extracts the link status information, session establishment availability information, and camera information contained in the acquired status notification information and updates the various information stored in the status storage unit 331 with the extracted information (step S33). Here, the link status information corresponding to the network camera 2B, which was unable to acquire an FLP burst, is set to "F10 (unconnected)." The terminal device 3 then forms display images including images indicated by the image information corresponding to each of the network cameras 2A, 2C, and 2D, and the first abnormality notification image for the network camera 2B, and stores display image information indicating the formed display images in the display image storage unit 322 (step S34). Next, the terminal device 3 displays on the display unit 304 the display image indicated by the display image information stored in the display image storage unit 322 (step S28). Here, if the terminal device 3 is unable to establish a link with network camera 2B, for example, it displays on the display unit 304 a display image GA2 in which images GA11, GA13, and GA14 indicated by the image information corresponding to network cameras 2A, 2C, and 2D, respectively, and a first abnormality notification image GA22 corresponding to network camera 2B are two-dimensionally arranged, as shown in FIG. 8(A). Here, the first abnormality notification image GA22 can be an image filled with a preset color or pattern, and is set to an image filled with black, for example.

As another example, as shown in the lower part of Figure 7, assume that a link has been established between the video distribution device 1 and network cameras 2A, 2B, 2C, and 2D, and that after the video distribution device 1 is powered on, a series of processes from step S1 to step S10 are executed. Thereafter, based on the acquired connection information, the video distribution device 1 determines that at least one of the network cameras 2A, 2B, 2C, and 2D, camera 2C, does not support RTP and that session establishment is impossible (step S35). In this case, the video distribution device 1 leaves the session establishment possibility information stored in the status memory unit 131 corresponding to network camera 2C, for which it has determined that session establishment is impossible, set to "F20 (session establishment impossible)," and sets the session establishment possibility information for the other cameras 2A, 2B, and 2D to "F21 (established)" (step S36). Next, the video distribution device 1 generates status notification information including the link status information, session establishment availability information, and camera information stored in the status storage unit 131 (step S37), and transmits the generated status notification information from the video distribution device 1 to the terminal device 3 (step S38). Meanwhile, upon acquiring the status notification information, the terminal device 3 extracts the link status information, session establishment availability information, and camera information contained in the acquired status notification information and updates the various information stored in the status storage unit 331 with the extracted information (step S39). Here, the session establishment availability information corresponding to network camera 2C, for which session establishment is impossible, is set to "F20 (establishment impossible)." The terminal device 3 then forms display images including images indicated by the image information corresponding to each of network cameras 2A, 2B, and 2D and the first abnormality notification image corresponding to network camera 2C, and stores display image information indicating the formed display images in the display image storage unit 322 (step S40). Next, the terminal device 3 displays on the display unit 304 the display image indicated by the display image information stored in the display image storage unit 322 (step S28). Here, if the terminal device 3 is unable to establish a session with network camera 2C, for example, it displays on the display unit 304 a display image GA3, in which images GA11, GA12, and GA14 indicated by the image information corresponding to network cameras 2A, 2B, and 2D, respectively, and a first abnormality notification image GA33 corresponding to network camera 2C are two-dimensionally arranged, as shown in FIG. 8(B). Here, the first abnormality notification image GA33 can be, for example, an image filled with a preset color or pattern, such as an orange image. However, in this case, the first abnormality notification image GA33 is an image with a different display style from the first abnormality notification image GA22 corresponding to network camera 2B, whose link is interrupted, as shown in FIG. 8(A).

9, assume that a link between the video distribution device 1 and network cameras 2A, 2B, 2C, and 2D has been established, a session can be established, and the video distribution device 1 is powered on, and then a series of processes from step S1 to step S23 are executed. Subsequently, assume that the terminal device 3 performs a restoration process on the image information stored in the compressed image buffer 321 (step S24), and determines that restoration has failed only for the image information corresponding to at least one of the network cameras 2A, 2B, 2C, and 2D, camera 2D (step S41). In this case, the terminal device 3 leaves the decode success/failure information stored in the status memory unit 331 corresponding to the network camera 2D that generated the image information that failed to be restored set to "F30 (failure)," and updates the decode success/failure information corresponding to 2A, 2B, and 2C to "F31 (success)" (step S42). Next, the terminal device 3 forms display images including images indicated by the image information corresponding to each of the network cameras 2A, 2B, 2C, and 2D and the first abnormality notification image described above, and stores display image information indicating the formed display images in the display image storage unit 322 (step S43). The terminal device 3 then displays the display images indicated by the display image information stored in the display image storage unit 322 on the display unit 304 (step S28). Here, if the terminal device 3 fails to restore the image information generated by the network camera 2D, for example, it displays a display image GA4 on the display unit 304, in which images GA11, GA12, and GA13 indicated by the image information corresponding to each of the network cameras 2A, 2B, and 2C, respectively, and a first abnormality notification image GA44 corresponding to the network camera 2D are two-dimensionally arranged, as shown in FIG. 10 . Here, the first abnormality notification image GA44 can be, for example, an image filled with a preset color or pattern, e.g., a green image. However, in this case, the first abnormality notification image GA44 uses an image with a different display format from the first abnormality notification image GA22 corresponding to the network camera 2B whose link is interrupted and the first abnormality notification image GA33 corresponding to the network camera 2C with which a session cannot be established.

Also, as shown in FIG. 11, after powering on the video distribution device 1, links between the video distribution device 1 and network cameras 2A, 2B, 2C, and 2D have been established, sessions can be established, and image information composite processing has been successful. Then, for example, a link interruption event occurs, interrupting the link with network camera 2B. Examples of such a link interruption event include a disconnection of the LAN cable between network camera 2B and the video distribution device 1 or a failure in the wired communication interface 206 of network camera 2B. In this case, the FLP burst transmitted from network camera 2B cannot be acquired. The video distribution device 1 then determines that the link with network camera 2B has been interrupted (step S29) and updates the link status information stored in the status memory unit 131 corresponding to the network camera 2B from which the FLP burst could not be acquired to "F10 (unconnected)" (step S30). Then, a series of processes from steps S31 to S33 are executed. Here, the link status information stored in the status storage unit 331 of the terminal device 3 is updated from "F11 (connected)" to "F10 (unconnected)" for the network camera 2B that was unable to acquire an FLP burst. The terminal device 3 then forms a display image including an image indicated by the image information corresponding to each of the network cameras 2A, 2B, 2C, and 2D and the second abnormality notification image corresponding to camera 2B, and stores the display image information indicating the formed display image in the display image storage unit 322 (step S44). Next, the terminal device 3 displays the display image indicated by the display image information stored in the display image storage unit 322 on the display unit 304 (step S28). Here, if the terminal device 3 is unable to establish a link with network camera 2B, for example, the terminal device 3 causes the display unit 304 to display a display image GA5 in which images GA11, GA13, and GA14 indicated by image information corresponding to network cameras 2A, 2C, and 2D, respectively, and a second abnormality notification image GA52 related to camera 2B are two-dimensionally arranged, as shown in FIG. 12(A). The second abnormality notification image GA52 reflects an image indicated by image information acquired from network camera 2B immediately before the link blocking event occurred, while superimposing an image indicating the occurrence of an abnormality. Specifically, the terminal device 3 causes the display unit 304 to display a preset second abnormality notification image GA52 different from the first abnormality notification image GA22. The second abnormality notification image GA52 includes, for example, an image GA521 immediately before the link blocking event occurred and a frame-shaped image GA522 arranged to surround the image GA521. Here, image GA522 can be a frame-shaped image of a preset color or pattern, and is set to, for example, a black rectangular frame image.

Suppose that a session establishment failure event occurs, making it impossible to establish a session with network camera 2C, as shown in the lower part of Figure 11. In this case, after the video distribution device 1 determines that a session establishment is not possible (step S35), it executes a series of processes from steps S36 to S39. Here, the session establishment link status information stored in the status memory unit 331 corresponding to network camera 2C, where the session opening event occurred, is updated from "F21 (establishment possible)" to "F20 (establishment not possible)." The terminal device 3 then updates the display image to include images indicated by the image information corresponding to each of network cameras 2A, 2B, 2C, and 2D and the aforementioned second abnormality notification image for camera 2C, and stores the display image information indicating the formed display image in the display image memory unit 322 (step S45). Next, the terminal device 3 displays the display image indicated by the display image information stored in the display image memory unit 322 on the display unit 304 (step S28). For example, if the terminal device 3 is unable to establish a link with network camera 2B and a session with network camera 2C, the terminal device 3 displays a display image GA6 on the display unit 304, in which images GA11 and GA14 representing image information corresponding to network cameras 2A and 2D, respectively, and second abnormality notification images GA52 and GA63 corresponding to network cameras 2B and 2C, respectively, are two-dimensionally arranged, as shown in FIG. 12(B). The second abnormality notification image GA63 has a different display format from the second abnormality notification image GA52, and includes, for example, an image GA631 of the image immediately before the occurrence of a session establishment impossible event and a frame-shaped image GA632 surrounding the image. The image GA632 can be a frame-shaped image of a preset color or pattern, such as an orange rectangular frame, different in color from the frame GA522 of GA52.

Also, as shown in FIG. 11, assume that an abnormality occurs in the encoding unit 211 of network camera 2D. In this case, the processes of steps S12 and S19 are executed. As shown in FIG. 13, which is a continuation of FIG. 11, after the series of processes of steps S20 through S23 are executed, the terminal device 3 performs a restoration process on the image information stored in the compressed image buffer 321 (step S24) and determines that restoration of the image information corresponding to network camera 2D has failed (step S41). In this case, the terminal device 3 updates the decode success/failure information stored in the status storage unit 331, corresponding to the network camera 2D that generated the original image information that failed to be restored, from "F31 (success)" to "F30 (failure)" (step S42). Next, the terminal device 3 forms display images including images indicated by the image information corresponding to each of network cameras 2A, 2B, 2C, and 2D and the second abnormality notification image, and stores display image information indicating the formed display images in the display image storage unit 322 (step S46). Thereafter, the terminal device 3 causes the display unit 304 to display the display image indicated by the display image information stored in the display image storage unit 322 (step S28). Here, for example, if the terminal device 3 is unable to establish a link with network camera 2B and a session with network camera 2C, and further fails to restore the image information corresponding to network camera 2D, the terminal device 3 causes the display unit 304 to display a display image GA7 in which an image GA11 indicated by the image information corresponding to network camera 2A and second abnormality notification images GA52, GA63, and GA74 corresponding to network cameras 2B, 2C, and 2D are two-dimensionally arranged, as shown in FIG. 14. Here, the second abnormality notification image GA74 has a display form different from the second abnormality notification images GA52 and GA63, and includes, for example, an image GA741 of the state immediately before the occurrence of an abnormality in the encoding unit 211 and a frame-shaped image GA742 arranged to surround the image GA741. Image GA742 can be a frame-shaped image of a preset color or pattern, and is set, for example, to a green rectangular frame image that is different from the color of GA522 and GA632.

Next, the video distribution process executed by the video distribution device 1 according to this embodiment will be described in detail with reference to Figure 15. This video distribution process is initiated, for example, when the video distribution device 1 is powered on. First, the link status determination unit 112 determines the link status with each of the network cameras 2A, 2B, 2C, and 2D (step S101). Here, it is assumed that the link status determination unit 112 determines, based on the FLP burst acquired by the connection processing unit 111, that negotiation with the network cameras 2A, 2B, 2C, and 2D has not been established and that the link is disconnected (step S101: No). In this case, the link status determination unit 112 updates the link status information stored in the status storage unit 131 corresponding to the network camera that has been determined to have its link disconnected from the network cameras 2A, 2B, 2C, and 2D to "F10 (not connected)" (step S102), and the status notification unit 116 generates the above-mentioned status notification information and transmits it to the terminal device 3 (step S103), after which the processing of step S101 is executed again. Meanwhile, it is assumed that the link status determination unit 112 determines, based on the FLP burst acquired by the connection processing unit 111, that negotiation with the network cameras 2A, 2B, 2C, and 2D has been established and that the link has been established (step S101: Yes). In this case, the link status determination unit 112 updates the link status information stored in the status storage unit 131 corresponding to the network cameras 2A, 2B, 2C, and 2D that have been determined to be connected to "F11 (connected)" (step S104), and the status notification unit 116 generates the aforementioned status notification information and transmits it to the terminal device 3 (step S105).

Next, the connection processing unit 111 determines whether the aforementioned session establishment event has occurred (step S106). If the connection processing unit 111 determines that a session establishment event has not occurred (step S106: No), the process of step S101 is executed again. On the other hand, if the connection processing unit 111 determines that a session establishment event has occurred (step S106: Yes), the connection processing unit 111 transmits the aforementioned connection information request information to the video distribution device 1 (step S107). Then, the connection processing unit 111 acquires the aforementioned connection information from the network cameras 2A, 2B, 2C, and 2D (step S108), generates communication start information based on the acquired connection information, and transmits it to the network cameras 2A, 2B, 2C, and 2D (step S109). Next, the connection processing unit 111 acquires response information transmitted from the network cameras 2A, 2B, 2C, and 2D (step S110), and the session determination unit 113 determines whether a session can be established with the network cameras 2A, 2B, 2C, and 2D (step S111). Here, let us assume that the session determination unit 113 determines, based on the response information acquired by the connection processing unit 111 from the network cameras 2A, 2B, 2C, and 2D, that one of the network cameras 2A, 2B, 2C, and 2D does not support RTP and that a session cannot be established (step S111: No). In this case, the session determination unit 113 sets the session establishment feasibility information stored in the status storage unit 131 corresponding to the network camera for which it has determined that a session cannot be established to "F20 (establishment not possible)" (step S112), and the status notification unit 116 generates the aforementioned status notification information and transmits it to the terminal device 3 (step S113), after which the processing of step S101 is executed again.

On the other hand, the session determination unit 113 determines, based on the response information acquired by the connection processing unit 111 from the network cameras 2A, 2B, 2C, and 2D, that the network cameras 2A, 2B, 2C, and 2D support RTP and that a session can be established (step S111: Yes). In this case, the session determination unit 113 updates the session establishment feasibility information stored in the status storage unit 131 and corresponding to the network cameras 2A, 2B, 2C, and 2D for which it has determined that a session can be established to "F21 (establishment possible)" (step S114), and the status notification unit 116 generates the aforementioned status notification information and transmits it to the terminal device 3 (step S115).

Then, the connection processing unit 111 transmits image transmission request information to the network cameras 2A, 2B, 2C, and 2D (step S116). When the connection processing unit 111 receives response information from the network cameras 2A, 2B, 2C, and 2D (step S117), the image acquisition unit 114 determines whether image information transmitted from the network cameras 2A, 2B, 2C, and 2D has been acquired (step S118). If the image acquisition unit 114 determines that image information has not been acquired (step S118: No), the process of step S120, described below, is executed. On the other hand, if the image acquisition unit 114 determines that image information has been acquired (step S118: Yes), the image acquisition unit 114 stores the acquired image information in the compressed image buffer 121. Then, the image transmission unit 115 transmits the image information stored in the compressed image buffer 121 to the terminal device 3 (step S119). Next, the connection processing unit 111 determines whether the aforementioned session opening event has occurred (step S120). If the connection processing unit 111 determines that a session open event has not occurred (step S120: No), the process of step S118 is executed again. On the other hand, if the connection processing unit 111 determines that a session open event has occurred (step S120: Yes), the process of step S101 is executed again.

Next, the video display process executed by the terminal device 3 according to this embodiment will be described in detail with reference to FIG. 16. This video display process is initiated, for example, after the terminal device 3 is powered on and an application for displaying images captured by the network cameras 2A, 2B, 2C, and 2D on the display unit 304 is launched. First, upon acquiring the status notification information transmitted from the video distribution device 1 (step S201), the status notification acquisition unit 314 extracts the link status information, session establishment availability information, and camera information contained in the acquired status notification information, associates these with each other, and stores them in the status storage unit 331 (step S202).

Next, the image acquisition unit 311 determines whether or not it has acquired image information transmitted from the video distribution device 1 (step S203). If the image acquisition unit 311 determines that it has not acquired image information (step S203: No), it executes the process of step S201 again. On the other hand, if the image acquisition unit 311 determines that it has acquired image information (step S203: Yes), it stores the acquired image information in the compressed image buffer 321 (step S204). Next, the decoding unit 312 performs a restoration process on the image information stored in the compressed image buffer 321 (step S205). Thereafter, the decoding determination unit 313 determines whether or not the restoration of the image information was successful as a result of the restoration process by the decoding unit 312 (step S206). Here, if the decoding determination unit 313 determines that the decoding unit 312 failed to restore the image information (step S206: No), it updates the decoding success/failure information for the corresponding network camera 2A, 2B, 2C, or 2D stored in the status storage unit 331 to "F30 (failure)" (step S207), and then executes the processing of step S209, described below. On the other hand, if the decoding determination unit 313 determines that the decoding unit 312 succeeded in restoring the image information (step S206: Yes), it updates the decoding success/failure information for the corresponding network camera 2A, 2B, 2C, or 2D stored in the status storage unit 331 to "F31 (success)" (step S208).

Then, the image forming unit 315 references the various information stored in the status memory unit 331 and determines whether all of the link status information, session establishment information, and decoding success/failure information for network cameras 2A, 2B, 2C, and 2D are "F11 (connected)," "F21 (established)," or "F31 (successful)" (step S209). Here, it is assumed that the image forming unit 315 determines that all of the link status information, session establishment information, and decoding success/failure information for network cameras 2A, 2B, 2C, and 2D are "F11 (connected)," "F21 (established)," or "F31 (successful)" (step S209: Yes). In this case, the image forming unit 315 forms display images including images corresponding to each of network cameras 2A, 2B, 2C, and 2D stored in the image memory unit 332, and stores the images in the display image memory unit 322 (step S210).

Meanwhile, suppose the image forming unit 315 determines that the link status information, session establishment information, or decoding success/failure information for one of the network cameras 2A, 2B, 2C, and 2D is "F10 (unconnected)," "F20 (unestablishable)," or "F30 (failed)" (step S209: No). In this case, the image forming unit 315 determines whether the link status information, session establishment information, or decoding success/failure information for the network camera 2A, 2B, 2C, or 2D for which the link status information, session establishment information, or decoding success/failure information is "F10 (unconnected)," "F20 (unestablishable)," or "F30 (failed)" has been updated most recently from "F11 (connected)" to "F10 (unconnected)," "F21 (establishable)" to "F20 (unestablishable)," or "F31 (successful)" to "F30 (failed)" (step S211). Here, let us assume that the image forming unit 315 determines that the most recent update was not from "F11 (connected)" to "F10 (not connected)," from "F21 (establishable)" to "F20 (not establishable)," or from "F31 (successful)" to "F30 (failed)" (i.e., the network camera was abnormal from the beginning) (step S211: No). In this case, the image forming unit 315 forms a display image including the first abnormality notification image corresponding to the network camera 2A, 2B, 2C, or 2D whose link status information, session establishment information, or decode success/failure information is "F10 (not connected)," "F20 (not establishable)," or "F30 (failed)," and stores the display image in the display image storage unit 322 (step S212). Thereafter, the process of step S214, which will be described later, is executed. On the other hand, suppose the image forming unit 315 determines that the network status was most recently updated from "F11 (connected)" to "F10 (unconnected)," from "F21 (establishable)" to "F20 (unestablishable)," or from "F31 (successful)" to "F30 (failed)" (step S211: Yes). In this case, the image forming unit 315 forms a display image including the second abnormality notification image corresponding to the network cameras 2A, 2B, 2C, and 2D for which any of the link status information, session establishment information, and decode success/failure information is "F10 (unconnected)," "F20 (unestablishable)," or "F30 (failed)," and stores the display image in the display image storage unit 322 (step S213). Next, the display control unit 316 displays the display image indicated by the display image information stored in the display image storage unit 322 on the display unit 304 (step S214). Subsequently, the process of step S201 is executed again.

As described above, with the video distribution device 1 according to this embodiment, the image forming unit 315 selects the display mode for the display unit 304 based on at least one of the link status with the network cameras 2A, 2B, 2C, and 2D, whether a session can be established, and the results of the restoration process for the image information. The image forming unit 315 then forms a display image in the selected display mode. As a result, if an abnormality occurs in the video distribution system, the display mode of the display image displayed on the display unit 304 changes depending on the cause of the abnormality. Therefore, the user can easily understand the cause of the abnormality by checking the display mode of the display image.

(Embodiment 2)
The video distribution system according to this embodiment differs from the first embodiment in that the video distribution device includes a decoding unit that executes a restoration process to restore image information, a restoration determination unit that determines whether the restoration of the image information was successful as a result of the restoration process, an encoding unit that compresses the input image information using a compression encoding method, and a transmission image buffer that temporarily stores the encoded image information. This embodiment will be described in detail below.

As shown in FIG. 17, the imaging system according to this embodiment includes network cameras 2A, 2B, 2C, and 2D, a video distribution device 2001, and a terminal device 2003. Note that in FIG. 17, the same components as those in embodiment 1 are assigned the same reference numerals as those in FIG. 3. The hardware configuration of the video distribution system according to this embodiment is also the same as that of the video distribution system described in embodiment 1. Therefore, the hardware configuration according to this embodiment will be described using the reference numerals shown in FIG. 2 as appropriate.

In the video distribution device 2001, the CPU 101 loads the programs stored in the auxiliary memory unit 103 into the main memory unit 102 and executes them, thereby functioning as a connection processing unit 111, link status determination unit 112, session determination unit 113, image acquisition unit 114, image transmission unit 115, decoding unit 2117, decoding determination unit 2118, image formation unit 2119, and encoding unit 2120. The main memory unit 102 also has a compressed image buffer 121 and a transmission image buffer 2122, and the auxiliary memory unit 103 has a status memory unit 2131.

The status storage unit 2131 stores information indicating the link status between each of the network cameras 2A, 2B, 2C, and 2D and the video distribution device 2001, information indicating whether a session can be established, and decode success/failure information indicating whether the image information restoration process was successful, in association with camera information indicating the camera number that identifies each of the corresponding network cameras 2A, 2B, 2C, and 2D.

The decoding unit 2117 generates restored image information by performing a restoration process on the image information stored in the compressed image buffer 121, and notifies the image forming unit 2119 of the generated image information. The decoding determination unit 2118 determines whether the image information has been successfully restored as a result of the restoration process performed by the decoding unit 2117. Each time the decoding unit 2117 performs a restoration process, the decoding determination unit 2118 generates decoding success/failure information indicating whether the image information has been successfully restored, and updates the decoding success/failure information stored in the status storage unit 2131.

The image forming unit 2119 selects the display mode of the display image to be displayed on the display unit 304 of the terminal device 2003 based on at least one of the link status information stored in the status storage unit 2131, session establishment success/failure information, and decode success/failure information indicating the result of the restoration process. The image forming unit 2119 then forms a display image in the selected display mode and notifies the encoding unit 2120 of display image information indicating the formed display image. More specifically, the image information acquired from each of the network cameras 2A, 2B, 2C, and 2D is composited based on the selected display mode, and the encoding unit 2120 is notified of display image information indicating the composite display image.

The encoding unit 2120 compresses the display image information notified by the image forming unit 2119 using the compression encoding method described in embodiment 1 and stores the compressed image in the transmission image buffer 2122. The image transmission unit 115 then transmits the display image information stored in the transmission image buffer 2122 to the terminal device 2003.

In the terminal device 3, the CPU 301 loads the program stored in the auxiliary memory unit 303 into the main memory unit 302 and executes it, thereby functioning as an image acquisition unit 311, a decoding unit 312, and a display control unit 316. The main memory unit 302 also has a compressed image buffer 321 and a display image storage unit 322. When the image acquisition unit 311 acquires display image information transmitted from the video distribution device 2001, it stores the acquired display image information in the compressed image buffer 321. The decoding unit 312 performs a restoration process on the display image information stored in the compressed image buffer 321 to generate restored image information and stores the generated image information in the display image storage unit 322. The display control unit 316 causes the display unit 304 to display the display image indicated by the display image information stored in the display image storage unit 322.

Next, the operation of the video distribution system according to this embodiment will be described with reference to Figures 18 and 19. Note that in Figures 18 and 19, the same processes as in embodiment 1 are assigned the same reference numerals as in Figures 5, 7, 9, and 11. First, as shown in Figure 18, when the video distribution device 2001 is powered on, a series of processes from steps S1 to S18 are executed, and then the network cameras 2A, 2B, 2C, and 2D identify image information to be sent to the video distribution device 2001 from the image information stored in the compressed image buffer 221 (step S19), and the identified image information is sent from the network cameras 2A, 2B, 2C, and 2D to the video distribution device 2001 (step S20). Meanwhile, when the video distribution device 2001 acquires image information, it stores the acquired image information in the compressed image buffer 121 (step S21).

Next, the video distribution device 2001 performs a restoration process on the image information stored in the compressed image buffer 121 (step S2001). Assume that the terminal device 2003 determines that the restoration of the image information was successful (step S2002). In this case, the video distribution device 2001 updates the decode success/failure information stored in the status memory unit 2131 for each of the network cameras 2A, 2B, 2C, and 2D to "F31 (success)" (step S2003). Next, the video distribution device 2001 forms a display image including an image indicated by the image information corresponding to each of the network cameras 2A, 2B, 2C, and 2D (step S2004). Thereafter, the video distribution device 2001 encodes the display image information indicating the formed display image and stores it in the transmission image buffer 2122 (step S2005). Next, the display image information stored in the transmission image buffer 2122 is transmitted from the video distribution device 2001 to the terminal device 2003 (step S2006). Meanwhile, upon acquiring the display image information, the terminal device 2003 stores the acquired display image information in the compressed image buffer 321 (step S2007).

Next, moving to FIG. 19, the terminal device 2003 performs a restoration process on the display image information stored in the compressed image buffer 321 using the decoding unit 312, and stores the display image information obtained by the restoration process in the display image storage unit 322 (step S2008). The terminal device 2003 then displays the display image indicated by the display image information stored in the display image storage unit 322 on the display unit 304 (step S2009).

Furthermore, the operation of the video distribution system in a situation where an abnormality occurs in the encoding unit 211 of the network camera 2D will be described using the diagram below the dashed line in Figure 19. In this case, after the processing of steps S16 and S19 is performed and the series of processing of steps S20 and S21 is performed, the video distribution device 2001 performs a restoration process on the image information stored in the compressed image buffer 121 (step S2001). Here, it is assumed that the video distribution device 2001 determines that restoration of the image information corresponding to the network camera 2D has failed due to an abnormality occurring during operation of the encoding unit 211 of the network camera 2D (step S2010). In this case, the video distribution device 2001 updates the decode success/failure information stored in the status memory unit 2131 for the network camera 2D that generated the image information that failed to be restored from "F31 (success)" to "F30 (failure)" (step S2011). Next, the video distribution device 2001 forms display images including images indicated by the image information corresponding to each of the network cameras 2A, 2B, 2C, and 2D and the second abnormality notification image corresponding to the network camera 2D (step S2012). The video distribution device 2001 then encodes the display image information indicating the formed display images and stores it in the transmission image buffer 2122 (step S2013). The display image information stored in the transmission image buffer 2122 is then transmitted from the video distribution device 2001 to the terminal device 2003 (step S2014). Meanwhile, upon acquiring the display image information, the terminal device 2003 stores the acquired display image information in the compressed image buffer 321 (step S2015). The terminal device 2003 then performs a restoration process on the display image information stored in the compressed image buffer 321 and stores the display image information obtained by the restoration process in the display image storage unit 322 (step S2016). The terminal device 2003 then displays the display image indicated by the display image information stored in the display image storage unit 322 on the display unit 304 (step S2017).

Next, the video distribution process executed by the video distribution device 2001 according to this embodiment will be described in detail with reference to Figures 20 and 21. Note that in Figures 20 and 21, processes similar to those in embodiment 1 are given the same reference numerals as in Figure 15. First, the link status determination unit 112 determines the link status with each of the network cameras 2A, 2B, 2C, and 2D (step S101). If the link status determination unit 112 determines that the link with any of the network cameras 2A, 2B, 2C, and 2D is disconnected (step S101: No), it updates the link status information stored in the status storage unit 2131 and corresponding to the network camera 2A, 2B, 2C, or 2D for which it has determined that the link is disconnected to "F10 (not connected)" (step S102), and further updates the session establishment availability information corresponding to the network camera 2A, 2B, 2C, or 2D for which it has determined that the link is disconnected to "F20 (establishment not possible)" (step S112), and the processing of step S2107, which will be described later, is executed. On the other hand, if the link status determination unit 112 determines that the links with all of the network cameras 2A, 2B, 2C, and 2D are established (step S101: Yes), the processing of steps S104 to S110 is executed. Next, if the session determination unit 113 determines that a session cannot be established with any of the network cameras 2A, 2B, 2C, and 2D (step S111: No), it updates the session establishment possibility information stored in the status storage unit 131 and corresponding to the network cameras 2A, 2B, 2C, and 2D for which it has been determined that a session cannot be established to "F20 (establishment not possible)" (step S112), and the processing of step S2107, described below, is executed.

On the other hand, if the session determination unit 113 determines that, for example, the network cameras 2A, 2B, 2C, and 2D support RTP and a session can be established (step S111: Yes), a series of processes from steps S114 to S117 are executed. Next, the image acquisition unit 114 determines whether image information transmitted from the network cameras 2A, 2B, 2C, and 2D has been acquired (step S2101). If the image acquisition unit 114 determines that image information from any of the network cameras has not been acquired (step S2101: No), the process of step S2115, described below, is executed. On the other hand, if the image acquisition unit 114 determines that image information has been acquired (step S2101: Yes), the image acquisition unit 114 stores the acquired image information in the compressed image buffer 121 (step S2102). Thereafter, the decoding unit 2117 performs a restoration process on the image information stored in the compressed image buffer 121 (step S2103). Next, as shown in FIG. 21 , the decoding determination unit 2118 determines whether the image information has been successfully restored as a result of the restoration process performed by the decoding unit 2117 (step S2104). If the decoding determination unit 2118 determines that the decoding unit 2117 has failed to restore the image information (step S2104: No), it updates the decode success/failure information for the corresponding network cameras 2A, 2B, 2C, and 2D stored in the status storage unit 2131 to "F30 (failure)" (step S2105), and then executes the processing of step S2107, described below. On the other hand, if the decoding determination unit 2118 determines that the decoding unit 2117 has successfully restored the image information for all cameras (step S2104: Yes), it updates the decode success/failure information for the corresponding network cameras 2A, 2B, 2C, and 2D stored in the status storage unit 2131 to "F31 (success)" (step S2106).

Next, the image forming unit 2119 determines whether any of the link status information, session establishment possible/possible information, and decode success/failure information status information has been updated for all network cameras 2A, 2B, 2C, and 2D (step S2107). Here, let us assume that the image forming unit 2119 has determined that the update process for the link status information, session establishment possible/possible information, and decode success/failure information status information has not yet been performed for any of the network cameras 2A, 2B, 2C, and 2D (step S2107: No). In this case, the process of step S101 is executed again. Meanwhile, let us assume that the image forming unit 2119 has determined that the update process for the link status information, session establishment possible/possible information, and decode success/failure information status information has been completed for all of the network cameras 2A, 2B, 2C, and 2D (step S2107: Yes). In this case, the image forming unit 2119 references various information stored in the status memory unit 2131 and determines whether all of the link status information, session establishment information, and decoding success/failure information for network cameras 2A, 2B, 2C, and 2D are "F11 (connected)," "F21 (established)," or "F31 (successful)" (step S2108). Assume that the image forming unit 2119 determines that all of the link status information, session establishment information, and decoding success/failure information for network cameras 2A, 2B, 2C, and 2D are "F11 (connected)," "F21 (established)," or "F31 (successful)" (step S2108: Yes). In this case, the image forming unit 2119 forms display images including images corresponding to network cameras 2A, 2B, 2C, and 2D stored in the compressed image memory unit 332, and stores the display image in the display image memory unit 322 (step S2109).

On the other hand, suppose the image forming unit 2119 determines that any of the link status information, session establishment information, and decode success/failure information for one of the network cameras 2A, 2B, 2C, and 2D is "F10 (unconnected)," "F20 (establishment not possible)," or "F30 (failure)" (step S2108: No). In this case, the image forming unit 2119 determines whether the network camera 2A, 2B, 2C, or 2D for which any of the link status information, session establishment information, and decode success/failure information is "F10 (unconnected)," "F20 (establishment not possible)," or "F30 (failure)" has transitioned from a normal state to an abnormal state or was previously in an abnormal state, i.e., whether it was recently updated from "F11 (connected)" to "F10 (unconnected)," from "F21 (establishment possible)" to "F20 (establishment not possible)," or from "F31 (success)" to "F30 (failure)" (step S2110). Here, let's assume that the image forming unit 2119 determines that the most recent update was not from "F11 (connected)" to "F10 (not connected)," "F21 (establishable)" to "F20 (not establishable)," or "F31 (successful)" to "F30 (failed)" (i.e., the abnormal state has continued from before) (step S2110: No). In this case, the image forming unit 2119 forms a display image including the first abnormality notification image described above for network cameras 2A, 2B, 2C, and 2D whose link status information, session establishment success/failure information, or decode success/failure information is "F10 (not connected)," "F20 (not establishable)," or "F30 (failed)" (step 2111). Then, the processing of step S2113, described below, is executed.

On the other hand, suppose the image forming unit 2119 determines that the status has been updated from "F11 (connected)" to "F10 (not connected)," from "F21 (establishable)" to "F20 (not establishable)," or from "F31 (successful)" to "F30 (failed)" (step S2110: Yes). In this case, the image forming unit 2119 forms a display image including the second abnormality notification image described above corresponding to the network cameras 2A, 2B, 2C, and 2D whose link status information, session establishment success/failure information, or decoding success/failure information is "F10 (not connected)," "F20 (not establishable)," or "F30 (failed)" (step 2112). The encoding unit 2120 then compresses the display image information representing the display image formed by the image forming unit 2119 using the compression encoding method described above, and stores the compressed image information in the transmission image buffer 2122 (step S2113). Next, the image transmission unit 115 transmits the display image information stored in the transmission image buffer 2122 to the terminal device 2003 (step S2114). The connection processing unit 111 then determines whether the aforementioned session open event has occurred (step S2115). If the connection processing unit 111 determines that a session open event has not occurred (step S2115: No), the process of step S2101 is executed again. On the other hand, if the connection processing unit 111 determines that a session open event has occurred (step S2115: Yes), the process of step S101 is executed again.

As described above, the video distribution device 2001 according to this embodiment determines whether image information acquired from network cameras 2A, 2B, 2C, and 2D can be decoded, and based on the determination result, forms a display image to be displayed on the display unit 304 of the terminal device 2003. This eliminates the need for the terminal device 2003 to determine whether image information acquired from network cameras 2A, 2B, 2C, and 2D can be decoded. Therefore, even if the terminal device 2003 does not have the function to determine whether image information acquired from network cameras 2A, 2B, 2C, and 2D can be decoded, it can display display images including the first abnormality notification image and second abnormality notification image described above on the display unit 405, thereby increasing the variety of terminal devices 2003 that can be used in the video distribution system according to this embodiment.

Although the above describes each embodiment of the present invention, the present invention is not limited to the configuration of each of the above-mentioned embodiments. For example, the network NW connecting the video distribution device 1 and the network cameras 2A, 2B, 2C, and 2D may be a wireless LAN. In this case, as shown in FIG. 22, when the video distribution device 1 is powered on, probe request information for searching for the network cameras 2A, 2B, 2C, and 2D is transmitted from the video distribution device 1 to the network cameras 2A, 2B, 2C, and 2D (step S3001). Meanwhile, when the network cameras 2A, 2B, 2C, and 2D receive the probe request information, probe response information including SSID information, channel information, etc. is transmitted from the network cameras 2A, 2B, 2C, and 2D to the video distribution device 1 in response (step S3002). Meanwhile, when the video distribution device 1 acquires the probe response information, authentication information for the network cameras 2A, 2B, 2C, and 2D to authenticate the video distribution device 1 is transmitted from the video distribution device 1 to the network cameras 2A, 2B, 2C, and 2D (step S3003). Assume now that the network cameras 2A, 2B, 2C, and 2D acquire the authentication information and are successful in authentication based on the acquired authentication information (step S3004). In this case, for example, the network cameras 2A, 2B, 2C, and 2D each identify themselves as devices that will wirelessly communicate with the video distribution device 1. Next, connection request information requesting connection to the network cameras 2A, 2B, 2C, and 2D is transmitted from the video distribution device 1 to the network cameras 2A, 2B, 2C, and 2D identified as devices that will wirelessly communicate with the video distribution device 1 (step S3005). On the other hand, when network cameras 2A, 2B, 2C, and 2D acquire the connection information request information, they transmit the connection information to video distribution device 1 in response (step S3006). On the other hand, when video distribution device 1 acquires the connection information, it executes the series of processes from step S8 onwards.

The video distribution device 1 may also be configured to communicate with network cameras 2A, 2B, 2C, and 2D via an access point (not shown) that is wired to the network cameras 2A, 2B, 2C, and 2D. In this case, the video distribution device 1 may transmit probe request information to the access point, obtain probe response information, and then transmit authentication information and connection request information to the access point. After obtaining connection response information from the access point, the video distribution device 1 may determine that a link with network cameras 2A, 2B, 2C, and 2D has been established.

With this configuration, the same effects as those of the embodiment can be achieved even if the network NW is configured as a wireless LAN.

In the embodiment, an example has been described in which the session determination unit 113 determines whether a session can be established by determining whether the network cameras 2A, 2B, 2C, and 2D support RTP based on the connection information acquired by the connection processing unit 111 from the network cameras 2A, 2B, 2C, and 2D. However, this is not limited to this. For example, when the image acquisition unit 114 acquires image information, the session determination unit 113 may determine whether a session can be established based on whether the header information corresponding to the application layer protocol included in the acquired image information is compatible with RTP.

Alternatively, for example, when the image acquisition unit 114 acquires image information, the session determination unit 113 may determine whether or not a session can be established depending on whether the format of the payload data of the image information matches a preset format. Alternatively, when the image acquisition unit 114 acquires image information, the session determination unit 113 may determine whether or not a session can be established depending on whether a code error is detected based on a checksum included in header information corresponding to the UDP included in the image information.

In the embodiment, an example has been described in which, when an abnormality occurs, the video distribution device 1 displays on the display unit 304 a second abnormality notification image that includes an image taken immediately before the abnormality occurred and a frame-shaped image surrounding the image. However, this is not limited to this, and when an abnormality occurs, the video distribution device 1 may also display on the display unit 304 a display image GA207 that includes second abnormality notification images GA252, GA263, and GA274, as shown in FIG. 18, for example.

In the embodiment, an example has been described in which compressed image information is transmitted from the video distribution device 1 to the terminal device 3, but this is not limiting. For example, the video distribution device 1 may decode the image information and then transmit the decoded image information to the terminal device 3. In this case, the video distribution device 1 may be configured to include a decoding unit (not shown) that performs a restoration process to restore the image information, and a decoding determination unit (not shown) that determines whether the restoration of the image information was successful as a result of the restoration process. The image transmission unit 115 may then transmit the decoded image information to the terminal device 3.

The various functions of the video distribution device 1 and terminal device 3 according to the present invention can be realized using a computer system equipped with a wireless communication module, rather than a dedicated system. For example, a program for executing the above operations may be stored on a non-transitory recording medium (such as a CD-ROM) that can be read by the computer system and distributed to a computer connected to a network. The video distribution device 1 and terminal device 3 that execute the above-described processes may then be configured by installing the program on the computer system.

Furthermore, the method for providing the program to the computer is arbitrary. For example, the program may be uploaded to a server on a communication line and distributed to the computer via the communication line. The computer then launches the program and executes it under the control of the OS in the same way as other applications. In this way, the computer functions as a video distribution device 1 and terminal device 3 that execute the above-mentioned processing.

The above describes embodiments and variations of the present invention, but the present invention is not limited to these. The present invention also includes appropriate combinations of the embodiments and variations, as well as appropriate modifications thereto.

This invention is suitable for video distribution systems that require setting camera numbers for multiple network cameras.

1, 2001: Video distribution device, 2A, 2B, 2C, 2D: Network camera, 3, 2003: Terminal device, 101, 201, 301: CPU, 102, 202, 302: Main memory unit, 103, 203, 303: Auxiliary memory unit, 106, 206: Wired communication interface, 107, 307: Wireless module, 109, 209, 309: Bus, 111, 212: Connection processing unit, 112: Link status determination unit, 113: Session determination unit, 114, 311: Image acquisition unit, 115, 213: Image transmission unit, 116: Status notification unit, 121, 221, 321: Compressed image buffer, 131, 331: Status memory unit, 204: Imaging unit, 211, 2120: Encoder 304: display unit, 312, 2117: decoding unit, 313, 2118: decoding determination unit, 314: status notification acquisition unit, 315, 2119: image forming unit, 316: display control unit, 322: display image storage unit, 332: image storage unit, 2122: transmission image buffer, GA1, GA2, GA3, GA4, GA5, GA6, GA 7: Display image; GA11, GA12, GA13, GA14, GA521, GA522, GA631, GA632, GA741, GA742: Images; GA22, GA33, GA44: First abnormality notification image; GA52, GA63, GA74, GA252, GA263, GA274: Second abnormality notification image; NW: Network

Claims (9)

a link status determination unit that determines a link status with the network camera;
a session determination unit that determines whether a session with the network camera can be established;
an image acquisition unit that acquires image information obtained by compressing an image captured by the network camera using a preset compression encoding method when a link with the network camera and a session are established;
a decoding unit that executes a restoration process to restore the image information;
a restoration determination unit that determines whether the restoration of the image information has been successful as a result of the restoration process;
an image forming unit that selects a display mode on a display unit based on at least one of the link state, whether the session can be established, and a result of the restoration process, and forms a display image in the selected display mode.
Video distribution system. The image forming unit forms a preset first abnormality notification image as the display image of the corresponding network camera if a state in which a link with the network camera is disconnected, a state in which a session with the network camera cannot be established, or a state in which restoration of the image information has failed continues immediately after startup of the video distribution system.
The video distribution system according to claim 1 . When an abnormality occurs and the image forming unit transitions to a state in which the link with the network camera is disconnected, a state in which the session with the network camera cannot be established, or a state in which restoration of the image information has failed, while a link with the network camera is established, a session with the network camera can be established, and restoration of the image information has been successful, the image forming unit forms, as the display image of the corresponding network camera, a second abnormality notification image that is different from the first abnormality notification image and that notifies the occurrence of an abnormality while displaying the image that reflects the image indicated by the image information acquired from the network camera immediately before the abnormality occurred.
The video distribution system according to claim 2 . There are a plurality of the network cameras,
the image forming unit forms the display image including the image indicated by the image information corresponding to each of the plurality of network cameras, the first abnormality notification image, or the second abnormality notification image;
The video distribution system according to claim 3 . A video distribution system that distributes image information captured by a network camera to a terminal device via a video distribution device connected to the network camera,
The video distribution device is
a link status determination unit that determines a link status with the network camera;
a session determination unit that determines whether a session with the network camera can be established;
an image acquisition unit that acquires image information obtained by compressing an image captured by the network camera using a preset compression encoding method when a link with the network camera and a session are established;
a decoding unit that executes a restoration process to restore the image information;
a restoration determination unit that determines whether the restoration of the image information has been successful as a result of the restoration process;
an image forming unit that selects a display mode on a display unit based on at least one of the link state, whether the session can be established, and a result of the restoration process, and forms a display image in the selected display mode.
Video distribution system. a link status determination unit that determines a link status with the network camera;
a session determination unit that determines whether a session with the network camera can be established;
an image acquisition unit that acquires image information obtained by compressing an image captured by the network camera using a preset compression encoding method when a link with the network camera and a session are established;
an image transmitting unit that transmits the acquired image information to a terminal device;
a status notification unit that generates status notification information indicating the link status and whether the session can be established and transmits the status notification information to the terminal device.
Video distribution device. an image acquisition unit that acquires image information obtained by compressing an image captured by a network camera using a preset compression encoding method;
a status notification acquisition unit that acquires status notification information transmitted from a video distribution device, the status notification information indicating a link status between the network camera and the video distribution device and whether a session can be established between the network camera and the video distribution device;
a decoding unit that executes a restoration process to restore the image information;
a restoration determination unit that determines whether the restoration of the image information has been successful as a result of the restoration process;
an image forming unit that selects a display mode on a display unit based on at least one of the link state and the possibility of session establishment indicated by the state notification information and a result of the restoration process, and forms a display image in the selected display mode.
Terminal device. determining a link status between the network camera and the video distribution device;
determining whether a session can be established between the network camera and the video distribution device;
acquiring image information obtained by compressing an image captured by the network camera using a preset compression encoding method when a link and a session between the network camera and the video distribution device are established;
performing a restoration process to restore the image information;
a step of determining whether the image information has been successfully restored as a result of the restoration process;
selecting a display mode on a display unit based on at least one of the link state, whether the session can be established, and a result of the restoration process, and forming a display image in the selected display mode.
Video distribution method. Computer,
a link status determination unit that determines the link status with the network camera;
a session determination unit that determines whether a session with the network camera can be established;
an image acquisition unit that acquires image information obtained by compressing an image captured by the network camera using a preset compression encoding method when a link with the network camera and a session are established;
a decoding unit that executes a restoration process to restore the image information;
a restoration determination unit that determines whether the restoration of the image information has been successful as a result of the restoration process;
an image forming unit that selects a display mode on a display unit based on at least one of the link state, whether the session can be established, and a result of the restoration process, and forms a display image in the selected display mode;
A program to function as a