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Re: Is it possible to record a MusicPlayer piece to an audio file faster than real-time?
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Re: Is it possible to record a MusicPlayer piece to an audio file faster than real-time?

  • Subject: Re: Is it possible to record a MusicPlayer piece to an audio file faster than real-time?
  • From: Archagon <email@hidden>
  • Date: Thu, 21 Apr 2016 22:45:17 -0700
Sorry to keep replying to myself, but I figured it out and thought I'd share my solution for posterity!

As the PlaySequence sample code[1] indicates, the trick is to use kAudioUnitSubType_GenericOutput instead of the default kAudioUnitSubType_RemoteIO. You also have to hook up your MusicTracks to actual AudioUnits, not virtual MIDI endpoints; kAudioUnitSubType_MIDISynth works best, but you have to preload your instruments as discussed here[2]. The kAudioUnitProperty_OfflineRender property doesn't work with the built-in iOS AudioUnits, but fortunately it's not required. Sadly, I don't think this process is currently possible with AVAudioEngine: you have to use AUGraph and friends.

Here's my updated sample code: https://github.com/archagon/aumidisynth-offline-render-test/blob/master/AVAudioEngineTest/ViewControllerAUGraph.m

[1]: https://developer.apple.com/library/mac/samplecode/PlaySequence/Listings/main_cpp.html
[2]: http://lists.apple.com/archives/coreaudio-api/2016/Jan/msg00015.html

On Wed, Apr 20, 2016 at 7:23 PM, Archagon <email@hidden> wrote:
Update: I made a prototype based on a StackOverflow answer[1], but unfortunately it sounds like all the MIDI events come in all at once, at the beginning of the offline recording: https://github.com/archagon/aumidisynth-offline-render-test/blob/master/AVAudioEngineTest/ViewController.m

Is there any way to solve this problem?

[1]: http://stackoverflow.com/a/30680391/89812

On Tue, Apr 19, 2016 at 1:12 AM, Archagon <email@hidden> wrote:
I have an iPad app that uses MusicPlayer (from AudioToolbox) to play MIDI files. Is it possible to run MusicPlayer "off the clock" (as fast as the CPU permits) and record the output to an audio file (WAV, etc.) faster than normal playback speed?


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References: 
 >Is it possible to record a MusicPlayer piece to an audio file faster than real-time? (From: Archagon <email@hidden>)
 >Re: Is it possible to record a MusicPlayer piece to an audio file faster than real-time? (From: Archagon <email@hidden>)

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