单个信道音频立体 - >单的AVPlayer播放(AVPlayer playback of s

在我的iPad / iPhone应用程序我使用AVPlayer播放视频。视频文件具有立体声音频轨道，但我需要回放只有一个这条赛道的单声道的通道。部署目标是iOS版6.如何才能做到这一点？非常感谢你的帮助。

我现在终于找到了这个问题的答案-至少在iOS 6的部署您可以轻松地你的程序回调函数中添加MTAudioProcessingTap到您现有的AVPlayer项目，并复制所选通道的样本给另一个信道。这里是一个伟大的教程解释的基本知识： http://chritto.wordpress.com/2013/01/07/processing-avplayers-audio-with-mtaudioprocessingtap/

这是到目前为止我的代码，大多是从上面的链接复制。

在AVPlayer设置我指定用于音频处理回调函数：

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, &callbacks,
                                          kMTAudioProcessingTapCreationFlag_PostEffects, &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;

下面是音频处理功能（实际上过程是需要的只有一个）：

#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->mBuffers[1].mData = bufferListInOut->mBuffers[0].mData;
        } else {
            bufferListInOut->mBuffers[0].mData = bufferListInOut->mBuffers[1].mData;
        }
    }
}