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

[Ross Finlayson]

>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.)
-- 

Ross Finlayson
Live Networks, Inc.
http://www.live555.com/

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