Question

Right now I have a loop that loops through an array of file player audio units and tells them what position in the audio file to start playing. (this works) In this same loop I have the following code to tell the units when to start playing (-1 makes them play in the next render cycle). The problem is that they are not starting at the same time because the first track starts playing before i have had a chance to tell the third track to play. What I want to say is “track one, you play in exactly 5 cycles, Track 2 you play in exactly 4 cycles, Track 3 you play in exactly 3 cycles… etc. that way they play at the same time. Is this the right approach? If so, what value do you set for startTime.mSampleTime ? I have not found any documentation that tells me how to do this. Thanks

    // tell the file player AU when to start playing (-1 sample time means next render cycle)
    AudioTimeStamp startTime;
    memset (&startTime, 0, sizeof(startTime));
    startTime.mFlags = kAudioTimeStampSampleTimeValid;
    startTime.mSampleTime = -1;
    AudioUnitSetProperty(fileUnitArray[mycount], kAudioUnitProperty_ScheduleStartTimeStamp, kAudioUnitScope_Global, 0, &startTime, sizeof(startTime));

Answer 1

I was not able to track down any information on setting mSampleTime to any other value then -1 (i.e start on the next cycle) but I was able to work around the problem. Instead of keeping the AUGraph running, using AudioUnitReset to reset the file player audio unit and then using the code above to restart the file players, I store the current file player play-head position, stop the AUGraph completely, reinitialize the AUGraph with the current play-head position instead of telling it to start at position zero, and then restart the AUGRAPH.