[Mp4-tech] [System]Audio video sync

[Jayant Chauhan]

Dear Dipankar and Bharat
1) Thanks fellas, but had thought of that. The problem I faced with
that approach was in implementing the clock, as in, if I use a TIMER,
it becomes process specific. So it would be nice if you could tell as
to how to implement a timer which runs on system time (if I have a
thread which keeps calling GETSYSTEMTIME, it will slow down the whole
system), so could you please suggest me the implementation of the
clock itself :D
2) Another problem I am facing (due to unavailability of the ISO
specs) is that in some of the standard ISO mpeg-4 streams provided,
like v10-transition.mp4, there are alot of visual tracks and they open
up in different windows when played in VLC player. Now how do I find
out as to which audio track is associated with which video ( as in,
how do I use the "tref" atom , assuming that is where I can get the
info from) and also as to one basic doubt, which follows in the next
query numbered 3 :)
3) In one moov, is it possible that that there be 2 video tracks !?? I
have some files which show 2 video tracks , with bothhaving the same
durations but one has only 1 sample and the other one is the main
video track. What is this video track with just 1 sample number ?!! Is
it just a JPEG (though  not shown as a JPEG).
thanking you in advance
with regards
Jayant
On Mon, 18 Oct 2023 15:55:55 +0530, Dipankar Mitra
<dipankar.mitra lgsoftindia.com> wrote:
> Thanks Bharat,
> Posting it to the mail list too...
> 
> Regards,
> Dipankar
> =============================================
> 
> Embassy Icon , 7th Floor
> Infantry Road
> Shivajinagar
> Bangalore - 560001
> Ph No. - 56938700 Ext : 177
> Fax      -  56938800
> 
> -----Original Message-----
> From: Bharat P. SONI [mailto:bharat.soni st.com]
> Sent: Monday, October 18, 2023 3:44 PM
> To: Dipankar Mitra
> Subject: RE: [Mp4-tech] [System]Audio video sync
> 
> Hi,
> 
> I did use the szstem time to synchronize the audio-video.
> Following are the steps I used to sznchroniye.
> 1. Make sure that all your timeing calculations, like clock
> time, CTS, DTS are relative to common reference start time.
> 
> 2. while decoding, check if the decoding time of the current
> access unit is less than current clock time. If yes then
> decode, otherwise discard that access unit.
> 2. store the decoded audio-video access units in queue along
> with their CTS.
> 
> For video,
> 1. get the next pending picture with lowest CTS, but greater
> than the current system time.
> 2. Schedule the timer for that CTS.
> 3. When timer hits, send the picture to the renderer.
> 
> For Audio
> 1. I worked on a system in which call back was being called
> whenever audio renderer finishes rendering the data in its
> buffer. So whenever the call back hits, check the CTS of
> audio access units in the queue and select the access unit
> having CTS closest to the current system time.
> 2. Send this access unit to the renderer.
> 3. remove all the access units having CTS less than current
> system time.
> 
> I hope this helps.
> 
> Regards,
> Bharat
> 
> 
> 
> 
> _______________________________________________
> NOTE: Please use clear subject lines for your posts. Include [audio, [video], [systems], [general] or another apppropriate identifier to indicate the type of question you have.
> 
> Note: Conduct on the mailing list is subject to the Antitrust guidelines found at http://www.mpegif.org/public/documents/vault/mp-out-30042-Antitrust.php
>