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admsyn / ofxAudioUnit

An openFrameworks addon which makes it easy to work with Audio Units on OSX and iOS
MIT License
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ofxAudioUnitFilePlayer::playAtSampleTime() acts the same as play() #23

Open jasonlevine opened 9 years ago

jasonlevine commented 9 years ago

Hi Adam,

I'm not sure if I've written about this before but recently noticed that calling playAtSampleTime(5 * 44100) will play the audio from the beginning of the file 5 seconds after the function call, which is exactly what play(5 * 44100) does. Logically, and from function definition, it seems like playAtSampleTime(5 * 44100) should start playing the audio file immediately from 5 seconds into the file. Is this correct? Is there a fix?

admsyn commented 9 years ago

Ah I guess the wording is a bit confusing. I think the reason I added that was to sync playback across multiple file players.

It's been awhile since I've looked at this code. I think the bit that controls your start frame is _region.mStartFrame, if you want to look into it yourself.

jasonlevine commented 9 years ago

Ok so I walked through the code in the Xcode debugger: playAtSampleTime(SR) sets _seekSampleTime to SR then calls play() play() calls prime() and then prime() sets _region.mStartFrame to SR

So: startTime = mach_absolute_time() and _region.mStartFrame = SR It seems like it should start playing immediately from 1 second into the track, but instead it starts from the beginning of the track, one second later.

Am I still misunderstanding? It seems like the intention of playAtSampleTime(SInt64 sampleTime) is to choose which sample of the audio file to start playback on by setting _region.mStartFrame to the desired frame when the region is primed as opposed to play(uint64_t startTime) where startTime is used create a timeStamp to schedule playback via FillOutAudioTimeStampWithHostTime(startTimeStamp, startTime);