[Mp4-tech] [System]Audio video sync

[Dipankar Mitra]

Hi Jayant,
	Most embedded players do use the audio time stamps or the actual audio play out time feedback as the guide. However, if you need to sync it with system time, you can try to retrieve the system time using whatever OS support is there for this and render the frames based on this. I've never tried this, so I'm not sure of the feasibility issues. 
Regards,
Dipankar
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-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org]On Behalf Of Jayant Chauhan
Sent: Friday, October 15, 2023 5:28 PM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] [System]Audio video sync
Hey fellas
Am working on  a media player for MP4 format. What I have is that I
have demuxed the audio and video tracks from the file. I can play the
video and audio by getting access units in 2 threads for each.
 Now I have to sync them. Could someone tell me how to go about it.
Rightnow I am syncing by the following method (though there is one big
glitch in it, in the sense that I dont have a real time timeline for
this) :
while (true){ 
 1) I fetch an audio sample and find its CTS (cummulative composition
time or duration ) and then play/render it, updating a AUDIOTIMESTAMP
variable.
2) Next I keep fetching video time samples till I have the closest
video from by doing
       while ( !  (abs( VIDEOTIMESTAMP - ATIMESTAMP) <= 10 ) ){
                 if ( VIDEOTIMESTAMP < ATIMESTAMP){
                      ... decode the frame but dont render it
                 }
        }
        // Now that we have the closest video frame from the current
audio played
        ...render the video frame.
}//end of while
This works fine, but if the CPU is really busy doing other stuff also,
I get into trouble, since here my refernce time line in a way is the
audio timeline and not the real system timeline.
  How do I do that ?!?!!
 Incase I comment the video or audio rendering, the file is played way
to fast, since I am not synchronizing with respect to realtime time
line
with regards
Jayant
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