AudioUnitRender and ExtAudioFileWrite -50 error in Swift: attempt to convert MIDI to audio file

Question

I am trying to convert a MIDI file to an audio file (.m4a) in Swift.

Now I use MIKMIDI as a tool for sequencing and playing MIDI files, however it does not include the ability to save the playback to a file. The creator of MIKMID describes the process to do this here . In an attempt to capture and save the output to a sound file, I used this example to try to replace the MIKMIDI Graph RemoteIO node with a GeneralIO node in Swift. When I try to save the output to a file using AudioUnitRender and ExtAudioFileWrite, they return a -50 error (kAudio_ParamError).

    var channels = 2
    var buffFrames = 512
    var bufferList = AudioBufferList.allocate(maximumBuffers: 1)

         for i in 0...bufferList.count-1{

               var buffer = AudioBuffer()
               buffer.mNumberChannels = 2
               buffer.mDataByteSize = UInt32(buffFrames*sizeofValue(AudioUnitSampleType))
               buffer.mData = calloc(buffFrames, sizeofValue(AudioUnitSampleType))

               bufferList[i] = buffer

               result = AudioUnitRender(generalIOAudioUnit, &flags, &inTimeStamp, busNum, UInt32(buffFrames), bufferList.unsafeMutablePointer)
               inTimeStamp.mSampleTime += 1

               result = ExtAudioFileWrite(extAudioFile, UInt32(buffFrames), bufferList.unsafeMutablePointer)

         }

-50, MIDI (offline) .m4a?

UPDATE. ExtAudioFileWrite -50, mNumberChannels channels = 1. . AudioUnitRender -50.

Answer 1

:

• AudioBufferList ,

  let bufferList = AudioBufferList.allocate(maximumBuffers: Int(clientFormat.mChannelsPerFrame)) 
  

• node AUGraph node , AudioUnitRender.

, , . , AudioUnitRender , , , "", midi-, .

, ( ) , , , - AudioUnitAddRenderNotify kAudioUnitRenderAction_PostRender.