[vlc] Re: Does VLC handle H.263 video over RTP?

[Kim Schulz]

On Mon, 30 Apr 2007 15:45:28 -0700
Ross Finlayson <finlayson at live555.com> wrote:

> >Reading this makes me a bit unsure whether my sdp for mp3 is wrong. I
> >was thought that the 22050 part was the sampling frequency and not
> >the timing (as opposed to the 90000 part).
> >So is mine wrong (besides the fact that it uses 14 and not 9x as
> >payload type). Is it important to change this payload type for VLC to
> >play the sound or?.
> 
> The frequency given in the SDP description (in the "a=rtpmap:") line 
> *must* be the frequency of the RTP timestamp.  The default RTP 
> timestamp frequency - for MPEG-1 or 2 audio or video (and many other 
> codecs) - is 90000.
> 
> This is not necessarily the same as the audio sampling frequency.  In 
> fact, for MPEG-1 or 2 audio (including MP3), the audio sampling 
> frequency will almost always be different from 90000.  (However, 
> because MPEG-1 or 2 audio frames are 'self describing', the audio 
> sampling frequency can be inferred from the audio data headers, and 
> therefore is not communicated at all in the SDP description.)
> 
> (For MPEG-*4* audio (AAC), however, the RTP timestamp frequency will 
> be the same as the audio sampling frequency, and must be indicated in 
> the "a=rtpmap:" line.)


Thanks for the help. 
Maybe you can also help me with the timestamp calculation then?
Previously I have just used the payload size (summed up) as timestamp,
but I guess that this will not work since it has nothing to do with the
90000 freq. 

-- 
    Kim Schulz       | Blog: http://www.schulz.dk/
Email: Kim at schulz.dk | Work: http://www.devteam.dk/
Phone: +45 5190 4262 | Fun : http://www.chilifan.dk/

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