Networked video surveillance, analog audio and video signals through the imaging, acquisition, encoding, digital audio and video streams transmitted over the network commonly known as "code stream." The two most important metrics that affect the quality of the video stream are "Video Resolution" and "Video Bit Rate."
Video resolution refers to the amount of information stored in each frame of image as it is encoded, measured in pixels per inch (PPI). At present, the mainstream resolution in the monitoring area is QCIF (176 × 144), CIF (352 × 288), and D1 (704 × 576). From the trend of development, HD resolutions of 1080p (1920 × 1080) and 720p ) Also gradually into people's attention.
Corresponding to the video resolution, the video bit rate refers to the rate at which video streams carry data in the channel, in bits per second (bps), indicating the bandwidth the video stream takes over the network.
Under normal circumstances, the greater the video resolution, the greater the video bit rate, the image clearer, but this is proportional to the video stream in the network bandwidth occupied by the greater the video decoding display occupied The more system resources. Therefore, when the video resolution used by the video surveillance is higher and higher, the existing Internet can hardly bear the video stream with an excessively large bit rate. The existing computer also has performance when performing multi-channel decoding on a high-resolution video Bottleneck In order to solve this problem, the concept of "dual stream" came into being. Double stream, as its name implies, will be compiled from the same video source two streams, the two streams can be the same resolution, you can also have different resolution.
Some manufacturers of network video front-end can be compiled with two streams of the same resolution, respectively, transmitted to the browsing client and storage server. This encoding and transmission mode, can fully reduce the monitoring host of the code stream forwarding pressure, but very easy to cause network congestion, only in the network bandwidth is very abundant occasions.
Some manufacturers of network video front-end can be compiled with two different streams of different resolutions, the resolution of the larger stream for video storage, the resolution of the smaller stream for real-time browsing. This can reduce the pressure on the network bandwidth occupied by remote browsing sufficiently, but the usage is not flexible enough and the user can only browse low-resolution images under ample bandwidth.
Based on the advantages and disadvantages of the above two methods, some NVR dual stream settings are more flexible. The NVR cooperates with the front end of the network to create two streams of different resolutions. The high-resolution stream is used as the local storage of the NVR. In real time, the NVR can automatically adjust the size of the user's browsing screen and the bandwidth of the user's network . For example: set the high-resolution stream to D1, then the stream viewed in real time can be automatically adjusted in D1, CIF and QCIF. This double code stream setting has two advantages:
1, in the case of the same video resolution, you can automatically adjust the resolution of the user according to the actual bandwidth size, so narrow-band users can use low-resolution video browsing, and more bandwidth users with high resolution For video browsing.
2, Under the condition of the same recording resolution, the resolution of the client screen can be automatically adjusted according to the way of dividing the client screen. When the user browses the large screen, the high-resolution stream is transmitted. When the user performs a small screen When browsing, it transmits a low-resolution stream. This can be fully used to improve the user's computer decoding efficiency.提
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