[Ffmpeg-devel] MPEG Documentation

Måns Rullgård mru
Fri Jun 10 22:32:17 CEST 2005

Mike Melanson <mike at multimedia.cx> writes:

> Lourenzo Dias wrote:
>>  Hello, guys!
>> I'm a student of Science of Computing, from Brazil. I have been
>> interested in MPEG codecs and players. I searched around for the
>> standards, but it's for sale. I don't have money to invest on ITU
>> standards, but I'm curious about it. I'm now trying to construct an
>> simulator of MPEG player in MATLAB, and would be wonderful if some
>> of you could send it for me.
> 	Google for "mpeg iso drafts" or something like that and you
> 	might find some useful specs.

IIRC, wotsit.org has a copy of some drafts.

>> I have a question that stoped me: How a player sincronizes the
>> exibition of the video? It uses the main board clock?
> 	Timing is entirely up to the player implementation. If they
> 	want to use the main board clock, fine. If they have some
> 	atomic clock time source available, they can use that too.

If there is an audio stream, I use the audio as the reference.  That
is, the I use the clock on the sound card.  This gives perfectly
synchronized playback, even if the sound card plays a little too fast
or too slow (most sound cards do).  If you are playing a live source
(streaming), the correct method is to somehow synchronize the local
clock with the server clock (that's what PCRs in MPEG-TS are for).  It
may then be necessary to resample the audio to compensate for an
inaccurate sound card clock.

M?ns Rullg?rd
mru at inprovide.com

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