[FFmpeg-user] Unable to record VP8+Opus from RTP+SDP

[Ted Park]

> Some updates: recording video actually works fine in both cases of only
> video and video+audio. A mistake in the video router was channeling
> audio frames to what should have been the video stream.

I think every instance of this working is because ffmpeg and the media players you tried are good at making educated guesses. 

The RTP payload format spec for opus is a proposed standard (rfc7587 <https://datatracker.ietf.org/doc/rfc7587/>) and the one for vp8 (rfc7741 <https://datatracker.ietf.org/doc/rfc7741/>) uses a profile of RTP that SDP hasn’t been updated to implement yet.

So I’m not sure how ffmpeg parses SDP files or if it uses a library but when you step back and take a look, you haven’t put in any specifics for either codec besides from maybe their names.

>   v=0
>   o=- 0 0 IN IP4 127.0.0.1
>   s=-
>   c=IN IP4 127.0.0.1
>   t=0 0
>   m=audio 5006 RTP/AVP 109
>   a=rtpmap:109 opus/48000/2
>   m=video 5004 RTP/AVP 120
>   a=rtpmap:120 VP8/90000

You can try reading the rfc’s and filling in the extra codec info it needs, but if you’re the one setting up the session, why not just use a simpler protocol? (I’m assuming the localhost is just a stand-in)

> However, the issue persists when trying to record Opus audio; it is just
> not possible to play it back, supposedly due to missing headers (but
> then how is it possible to record incoming RTP Opus audio?)

Like, you told ffmpeg it was going to be 48khz, 2 chs it believed your copy codec and just dumped everything into a file. But when you open up the file, does it really have two channels? is the audio interleaved? Nobody knows.