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    <p>I now finally found an answer to this question - at least for deployment on iOS 6. You can easily add an <strong>MTAudioProcessingTap</strong> to your existing AVPlayer item and copy the selected channels samples to the other channel during your process callback function. Here is a great tutorial explaining the basics: <a href="http://chritto.wordpress.com/2013/01/07/processing-avplayers-audio-with-mtaudioprocessingtap/" rel="nofollow">http://chritto.wordpress.com/2013/01/07/processing-avplayers-audio-with-mtaudioprocessingtap/</a></p> <p>This is my code so far, mostly copied from the link above.</p> <p>During AVPlayer setup I assign callback functions for audio processing:</p> <pre><code>MTAudioProcessingTapCallbacks callbacks; callbacks.version = kMTAudioProcessingTapCallbacksVersion_0; callbacks.clientInfo = ( void *)(self); callbacks.init = init; callbacks.prepare = prepare; callbacks.process = process; callbacks.unprepare = unprepare; callbacks.finalize = finalize; MTAudioProcessingTapRef tap; // The create function makes a copy of our callbacks struct OSStatus err = MTAudioProcessingTapCreate(kCFAllocatorDefault, &amp;callbacks, kMTAudioProcessingTapCreationFlag_PostEffects, &amp;tap); if (err || !tap) { NSLog(@"Unable to create the Audio Processing Tap"); return; } assert(tap); // Assign the tap to the input parameters audioInputParam.audioTapProcessor = tap; // Create a new AVAudioMix and assign it to our AVPlayerItem AVMutableAudioMix *audioMix = [AVMutableAudioMix audioMix]; audioMix.inputParameters = @[audioInputParam]; playerItem.audioMix = audioMix; </code></pre> <p>Here are the audio processing functions (actually process is the only one needed):</p> <pre><code>#pragma mark Audio Processing void init(MTAudioProcessingTapRef tap, void *clientInfo, void **tapStorageOut) { NSLog(@"Initialising the Audio Tap Processor"); *tapStorageOut = clientInfo; } void finalize(MTAudioProcessingTapRef tap) { NSLog(@"Finalizing the Audio Tap Processor"); } void prepare(MTAudioProcessingTapRef tap, CMItemCount maxFrames, const AudioStreamBasicDescription *processingFormat) { NSLog(@"Preparing the Audio Tap Processor"); } void unprepare(MTAudioProcessingTapRef tap) { NSLog(@"Unpreparing the Audio Tap Processor"); } void process(MTAudioProcessingTapRef tap, CMItemCount numberFrames, MTAudioProcessingTapFlags flags, AudioBufferList *bufferListInOut, CMItemCount *numberFramesOut, MTAudioProcessingTapFlags *flagsOut) { OSStatus err = MTAudioProcessingTapGetSourceAudio(tap, numberFrames, bufferListInOut, flagsOut, NULL, numberFramesOut); if (err) NSLog(@"Error from GetSourceAudio: %ld", err); SIVSViewController* self = (SIVSViewController*) MTAudioProcessingTapGetStorage(tap); if (self.selectedChannel) { int channel = self.selectedChannel; if (channel == 0) { bufferListInOut-&gt;mBuffers[1].mData = bufferListInOut-&gt;mBuffers[0].mData; } else { bufferListInOut-&gt;mBuffers[0].mData = bufferListInOut-&gt;mBuffers[1].mData; } } } </code></pre>
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    1. POAVPlayer playback of single channel audio stereo->mono
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    1. USAndreas Zöllner
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    1. COHey, looking for a solution to play TTS sounds on one headphone channel. Your code could be helpful or do you have any tips?
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      1. USBen Hutchinson
 

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