[FFmpeg-devel] [PATCH] sdp: optional 'vbr' parameter for Speex RTP payload

[Dmitry Samonenko]

On Tue, Oct 09, 2012 at 10:50:33PM +0200, Michael Niedermayer wrote:
> I dont think this will work with stream copy, that is for example
> something like:
> 
> ffmpeg -i test.mov -acodec copy -f rtp rtp://127.0.0.1:1234
> the mov file here would contain a speex stream
> 

Yeah, I understand this too now.

Well, I guess in that case each avformat supporting speex should be
made capable (if it can be) to spot vbr operation mode.

As for your example concerning mov, I made some research: stsd atom
doesn't have a place for a such flag (vbr operation). But QuickTime
file generated by ffmpeg contains glbl atom with full speex header
(vbr field is present). I haven't found anything about if it's a
regular behavior among QuickTime muxers or not.
In fact, I haven't found anything about glbl atom at all.

So, I think I look into Xiph OGG format then, which AFAIK should
contain full speex header, get some ideas about which AVCodecContext
fields should be used to signal speex vbr operation mode and decide
later how to act in case of `non-speex-friendly' input format is used
for stream copy.