In networked video surveillance, after the analog audio and video signals are imaged, collected, and coded, the digital audio and video streams transmitted over the network are commonly referred to as "streams." The two most important indicators that affect the quality of video streaming are "video resolution" and "video bit rate."
Video resolution refers to the amount of information stored in each frame of an image, measured in pixels per inch (PPI). Currently, the mainstream resolution in the surveillance field is QCIF (176×144), CIF (352×288), and D1 (704×576). From the trend of development, HD resolutions are 1080p (1920×1080) and 720p (1280×720). ) Also gradually entered the people's attention.
Corresponding to the video resolution, the video bit rate refers to the rate at which the video stream transmits data in the channel, in units of bits per second (bits per second), which indicates the bandwidth that the video stream occupies in the network transmission.
Under normal circumstances, the greater the video resolution, the larger the video bit rate and the clearer the picture, but in proportion to this, the bandwidth that the video bitstream occupies in the network transmission is also greater, and the video decoding display is occupied. The more system resources are. Therefore, when the video resolution used by the video surveillance is getting higher and higher, the existing internetwork can hardly bear the video stream with too high bitrate, and the existing computer also has performance when multi-channel decoding is performed on high-resolution video. The bottleneck. In order to solve this problem, the concept of "dual stream" came into being. Dual stream, as the name implies, compiles the same video source into two streams. The two streams can be of the same resolution or different resolutions.
Some manufacturers' network video front-ends can compile two streams of the same resolution and transmit them to the browsing client and storage server respectively. This encoding and transmission method can fully reduce the pressure of the monitoring host's code stream forwarding, but it is very easy to cause network congestion and can only be used when the network bandwidth is very abundant. As shown below:
Some manufacturers' network video front-ends can encode two streams with different resolutions. The larger-resolution stream is used for video storage, and the lower-resolution stream is used for real-time browsing. This can fully reduce the pressure of network bandwidth occupied by remote browsing, but the usage is not flexible enough, and users can only browse low-resolution images when the bandwidth is sufficient. As shown below:
Comprehensive advantages and disadvantages of the above two methods, some NVR's dual stream settings are more flexible. The NVR cooperates with the network front end and can compile two streams with different resolutions. The high resolution stream is used as the NVR local storage. In real-time browsing, it can be automatically adjusted according to the size of the user's browsing screen and the network bandwidth of the user. . For example, if you set the high-resolution stream to D1, the stream for real-time browsing can be automatically adjusted in D1, CIF, and QCIF. This dual stream setup has two advantages:
1. In the case of the same video resolution, the resolution can be automatically adjusted according to the user's actual bandwidth, so that narrow-band users can use low-resolution video browsing, while users with more bandwidth have higher resolution. For video browsing.
2. In the case of the same video resolution, the resolution can be automatically adjusted according to the way the user uses the screen segmentation of the client. When the user browses the large screen, the high-resolution stream is transmitted, and the user is performing a small screen. While browsing, the low resolution stream is transmitted. This can fully improve the decoding efficiency of the computer used by the user.
Video resolution refers to the amount of information stored in each frame of an image, measured in pixels per inch (PPI). Currently, the mainstream resolution in the surveillance field is QCIF (176×144), CIF (352×288), and D1 (704×576). From the trend of development, HD resolutions are 1080p (1920×1080) and 720p (1280×720). ) Also gradually entered the people's attention.
Corresponding to the video resolution, the video bit rate refers to the rate at which the video stream transmits data in the channel, in units of bits per second (bits per second), which indicates the bandwidth that the video stream occupies in the network transmission.
Under normal circumstances, the greater the video resolution, the larger the video bit rate and the clearer the picture, but in proportion to this, the bandwidth that the video bitstream occupies in the network transmission is also greater, and the video decoding display is occupied. The more system resources are. Therefore, when the video resolution used by the video surveillance is getting higher and higher, the existing internetwork can hardly bear the video stream with too high bitrate, and the existing computer also has performance when multi-channel decoding is performed on high-resolution video. The bottleneck. In order to solve this problem, the concept of "dual stream" came into being. Dual stream, as the name implies, compiles the same video source into two streams. The two streams can be of the same resolution or different resolutions.
Some manufacturers' network video front-ends can compile two streams of the same resolution and transmit them to the browsing client and storage server respectively. This encoding and transmission method can fully reduce the pressure of the monitoring host's code stream forwarding, but it is very easy to cause network congestion and can only be used when the network bandwidth is very abundant. As shown below:
Some manufacturers' network video front-ends can encode two streams with different resolutions. The larger-resolution stream is used for video storage, and the lower-resolution stream is used for real-time browsing. This can fully reduce the pressure of network bandwidth occupied by remote browsing, but the usage is not flexible enough, and users can only browse low-resolution images when the bandwidth is sufficient. As shown below:
Comprehensive advantages and disadvantages of the above two methods, some NVR's dual stream settings are more flexible. The NVR cooperates with the network front end and can compile two streams with different resolutions. The high resolution stream is used as the NVR local storage. In real-time browsing, it can be automatically adjusted according to the size of the user's browsing screen and the network bandwidth of the user. . For example, if you set the high-resolution stream to D1, the stream for real-time browsing can be automatically adjusted in D1, CIF, and QCIF. This dual stream setup has two advantages:
1. In the case of the same video resolution, the resolution can be automatically adjusted according to the user's actual bandwidth, so that narrow-band users can use low-resolution video browsing, while users with more bandwidth have higher resolution. For video browsing.
2. In the case of the same video resolution, the resolution can be automatically adjusted according to the way the user uses the screen segmentation of the client. When the user browses the large screen, the high-resolution stream is transmitted, and the user is performing a small screen. While browsing, the low resolution stream is transmitted. This can fully improve the decoding efficiency of the computer used by the user.
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