Analysis of the principle of SRT Protocol

The basic idea of SRT

The above picture can cover the basic idea of SRT: compare the encoded video and audio stream (the green broken line "Source" on the left) and the stream after the public network transmission (red broken line "NetworkTransmission"), you can see the encoded source The video and audio code stream has a fixed frame interval and a variable bit rate with certain characteristics. However, the frame interval of the code stream after transmission through the public network becomes unstable and the bit rate characteristics are completely changed. Decoding such a signal is a This is a very difficult challenge, even impossible to decode.

However, if the SRT protocol with error correction is used for public Internet transmission, although the encoded video and audio stream becomes unstable through the public network transmission frame interval, because the SRT protocol encapsulation contains accurate time stamps, the decoding receiver can pass The time stamp reproduces a fixed frame interval. More importantly, by specifying the amount of delay, the send buffer and receive buffer are defined at the same time, and the feedback signal from the receiving end (which can be understood as backward error correction) passes through a series of The setting, error correction, and flow control of the video and audio stream after encoding have almost the same bit rate characteristics as the original stream.

The data processed by the Encoder encoder will be input into the send buffer, and the send buffer will time-check the data, that is, encode in a certain time sequence and send it to the receivebuffer through the internet. The receive buffer is processed a little bit according to the timestamp on the message , To ensure that the generated data is basically consistent with the source code stream.The idea of the entire SRT protocol is based on coding, which has features such as anti-packet loss, anti-congestion, and anti-jitter.

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