[Mp4-tech] [System]Audio video sync

[Jayant Chauhan]

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