Question

I’m trying to use a file player audio unit (kAudioUnitSubType_AudioFilePlayer) to play multiple files (not at the same time, of course). That’s on iOS.
So I’ve successfully opened the files and stored their details in an array of AudioFileID‘s that I set to the audio unit using kAudioUnitProperty_ScheduledFileIDs. Now I would like to define 2 ScheduledAudioFileRegion‘s, one per file, and used them with the file player…

But I can’t seem to find out:

• How to set the kAudioUnitProperty_ScheduledFileRegion property to store these 2 regions (actually, how to define the index of each region)?
• How to trigger the playback of a specific region.. My guess is that the kAudioTimeStampSampleTimeValid parameter should enable this but how to define which region you want to play?

Maybe I’m just plain wrong about the way I should use this audio unit, but documentation is very difficult to get and I haven’t found any example showing the playback of 2 regions on the same player!
Thanks in advance.

Answer 1

You need to schedule region every time you want play file. In ScheduledAudioFileRegion you must set AudioFileID to play. Playback begins when current time in unit (samples) are equal or greater than sample time in scheduled region.

Example:

// get current unit time
AudioTimeStamp timeStamp;
UInt32 propSize = sizeof(AudioTimeStamp);
AudioUnitGetProperty(m_playerUnit, kAudioUnitProperty_CurrentPlayTime, kAudioUnitScope_Global, 0, &timeStamp, &propSize);

// when to start playback
timeStamp.mSampleTime += 100;

// schedule region

ScheduledAudioFileRegion region;
memset(&region, 0, sizeof(ScheduledAudioFileRegion));
region.mAudioFile = ...; // your AudioFileID
region.mFramesToPlay = ...; // count of frames to play
region.mLoopCount = 1;
region.mStartFrame = 0;
region.mTimeStamp = timeStamp;


AudioUnitSetProperty(m_playerUnit, kAudioUnitProperty_ScheduledFileRegion, kAudioUnitScope_Global, 0, &region,sizeof(region));