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AudioQueueStart with startTime in the past
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AudioQueueStart with startTime in the past


  • Subject: AudioQueueStart with startTime in the past
  • From: Paul Doersch <email@hidden>
  • Date: Tue, 1 Sep 2009 20:38:50 +0200

Hello all, I am using CoreAudio to do some audio track synchronization. The function AudioQueueStart(AudioQueueRef aq, AudioTimeStamp* startTime) can take a timestamp for when to start. That timestamp can also be in the past, and CoreAudio automatically spools forward and begins playing where it would be had it actually started back at the timestamp.

The problem is, it doesn't seem to do it perfectly. This process of spooling forward I mentioned, seems to take a bit of time and messes up the AudioQueue's timekeeping. When I say spooling forward I mean getting the 

AudioInMem_ReadProc ( void     *inClientData,
SInt64    inPosition,
UInt32    requestCount,
void     *buffer,
UInt32   *actualCount)

callbacks multiple times in a row right before playing. So, how should I handle this? How can one prime the AudioQueue when the start time is in the past, and quite a bit of spooling forward is required before we reach the right spot in memory?

Thanks!
-Paul
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