H264 spreader

[jvary]

REQUEST FOR COMMENTS:
H264 spreader : reduces the RTP payload size so 3rd parties RTP sources can be properly redirected over SRTP/WebRTC without IP fragmentation.

High level steps:

• Passes RTP content straight if possible
  • (if not FUA & not too big)
  • might RtpSeq offset if needed
• Splits StapA in sub-nals
  • (and then sub-nals in FUA if still too big)
• Splits StandAlone NAL in FUA
• Spreads FUA in smaller FUA, carrying 'trailing data' to maximize the size of each FUA nal.
  • (flushing the trailing on RtpSequence discontinuity or change of type)

The steps above handle :

• RtpSeq offset/adjustment of each packet
• Rtp Marker 'delay'
• 'Delay' of FUA 'end' bit if needed.

Advantages vs building whole H264 Frame as you initially proposed:

• many packets just go through after two 'if'
• less memory footprint
• more continuous flow / less data burst
• RTP sequence holes are 'kept', so it is easier to track quality / packet loss

Future improvement: back-buffer to persist between Process(), to avoid making new buffer for each new returned RTP.

[email protected]

[jvary]

Ok, it looks like there is little interest for this PR/feature, so closing it.

[Sean-Der]

Hi @jvary i would like to take this! I am just very overwhelmed with PRs

[Sean-Der]

I will review and address all issues myself :)

[jvary]

Oh! Glad there is interest!
We continued development in-house (and fixed 1-2 bugs as well), so I will update this PR.
@Sean-Der : question : would you rather have the 'interface' dealing with raw slices (as right-now), or have rtp.Packet in input/output ?

[Sean-Der]

Hey @jvary

Sorry it has been over 3 years O_O but I am going to get this merged! I will fix all the lint errors/etc... and would love your take!

I think this is super valuable to have. Even if only one other person uses it I am so happy to have this code Open Source/available for others to read :)

[codecov]

Codecov Report

❌ Patch coverage is 78.23834% with 42 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.75%. Comparing base (8c22f58) to head (70bf0aa).

Files with missing lines	Patch %	Lines
codecs/h264/spreader.go	78.23%	32 Missing and 10 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #194      +/-   ##
==========================================
- Coverage   91.73%   90.75%   -0.99%     
==========================================
  Files          26       27       +1     
  Lines        2445     2638     +193     
==========================================
+ Hits         2243     2394     +151     
- Misses        140      172      +32     
- Partials       62       72      +10     

Flag	Coverage Δ
go	90.75% <78.23%> (-0.99%)	⬇️

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