[MediaRelay] Add support for unbuffered to MediaRelay

[Laityned]

Support for unbuffered RelayStreamTrack, to ensure no delay between the original track and relayed track

[codecov]

Codecov Report

Merging #498 (2bc25c6) into main (01ff209) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #498   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           31        31           
  Lines         5669      5681   +12     
=========================================
+ Hits          5669      5681   +12     

Impacted Files	Coverage Δ
src/aiortc/contrib/media.py	100.00% <100.00%> (ø)

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[jlaine]

This looks very cool, I'll take it for a spin. Could we add an explanation of the buffered argument to the doc string?

[Laityned]

Added param to docstring

[johnboiles]

I tried this out with the webcam.py example but wasn't able to see a difference in video latency. Are you seeing noticeable latency introduced by the buffering in MediaRelay?

[Laityned]

On a single videostream, it is not noticable. However when using a larger number of clients, you will reach a point where your asyncio event loop is slower than framerate of the camera.

Since the camera is in a seperate thread it keeps filling the buffer, while the clients suffer from a drop in framerate due to the performance issues of the asyncio event loop.

The buffer will keep increasing and could lead to a out of memory. Also since the buffer is filling at a faster rate than the frames are transmitted an increased latency will occur between the client and webcam server.

[johnboiles]

Got it. I experimented with it a bit more and with multiple clients connected on a Pi, it would definitely start dropping frames. This means if an I-frame gets dropped, the video gets all messed up for a bit. But probably better than OOM-ing!