[FFmpeg-user] Reading RTP from file/stdin

Daire Quinlan daire.quinlan at gmail.com
Fri Mar 9 20:09:42 EET 2018

Hi all,

I'm trying to work out how to do something which may be impossible using
ffmpeg , but I want to check before going down a rabbit hole.

I have a file with RTP packets representing an audio conversation. Format
is g729. Stripping out the actual RTP payload (i.e. the raw g729 payload)
and piping it to ffmpeg and specifying the format I can successfully write
out a wav file (or whatever) so the content is good.

If I try and run ffmpeg against the RTP packets though I get the following:

[rtp @ 0x4b67c40] Unable to receive RTP payload type 18 without an SDP file
describing it

This is expected, as I understand it, ffmpeg expects an accompanying SDP to
parse the RTP correctly. I can, of course, specify an SDP that corresponds
to the RTP, but the problem is that I do NOT want to stream from a network
endpoint. I want to parse that file that I have containing the RTP packets.
IS there a way to do this at the moment with ffmpeg ?

All the information required is in the RTP headers, so network issues aside
it seems that ffmpeg (and the rtp parser) should be able to just parse an
rtp file, though I guess it hasn't been implemented that way.


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