Subject: [MMUSIC] Audio Video synchronization

From: Vinod Madhav Joshi <[email-masked]>
Date: Thu, 12 Jul 2007 11:14:17 +0530

Hi all,

   We are receiving MPEG2 demuxed elementary audio and video streams
   from streaming server o the set top box.
   The source for audio and video is the same.
   I want to know how to synchronise this audio and video data using
   RTP timestamps.
   i. e. how to generate Presentation Timestamps.
   For synchronization using RTP timestamps is it mandatory to use
   the RTCP packets?

   Please help me.

   Thank You.

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From: Joerg Ott <[email-masked]>
Date: Thu, 12 Jul 2007 09:01:37 +0300

Hi,

(this is probably a question for the AVT WG mailing list)

>    For synchronization using RTP timestamps is it mandatory to use

yes.  Both media streams, audio and video, have their own internal
clock which are naturally different.  RTCP packets relate the
internal clock to wallclock time (which is simply the clock of
the sender, so that no time-synchronization between sender and
receiver devices is needed).  As you know the clock rate of each
stream and you get regular references to wall clock time,
you can compute on the receiver side which media time stamps
have to be played back at the same time and dimension your
playout delay accordingly.

Joerg