在IOS中重复音频的损坏记录

Question

我的应用程序在iPhone上记录流媒体音频。我的问题是，一小部分(约2%)的录音是损坏的。他们似乎有一些音频缓冲区重复。

例如，听这个文件

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Edit:令人惊讶的是，使用Audacity仔细查看数据会发现重复的部分非常非常相似，但并不完全相同。由于FLAC(我用于编码音频的格式)是一种无损压缩，我想这不是流/编码中的错误，但问题源于来自麦克风的数据!

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下面是我用来设置音频录制流的代码-有什么问题吗?

// see functions implementation below
- (void)startRecording
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
               , ^{
        [self setUpRecordQueue];
        [self setUpRecordQueueBuffers];
        [self primeRecordQueueBuffers];
        AudioQueueStart(recordQueue, NULL);
    });
}

// this is called only once before any recording takes place
- (void)setUpAudioFormat
{
    AudioSessionInitialize(
                           NULL,
                           NULL,
                           nil,
                           (__bridge  void *)(self)
                           );
        UInt32 sessionCategory = kAudioSessionCategory_PlayAndRecord;
        AudioSessionSetProperty(
                            kAudioSessionProperty_AudioCategory,
                            sizeof(sessionCategory),
                            &sessionCategory
                            );
        AudioSessionSetActive(true);
    audioFormat.mFormatID         = kAudioFormatLinearPCM;
    audioFormat.mSampleRate       = SAMPLE_RATE;//16000.0;
    audioFormat.mChannelsPerFrame = CHANNELS;//1;
    audioFormat.mBitsPerChannel   = 16;
    audioFormat.mFramesPerPacket  = 1;
    audioFormat.mBytesPerFrame    = audioFormat.mChannelsPerFrame * sizeof(SInt16);
    audioFormat.mBytesPerPacket   = audioFormat.mBytesPerFrame * audioFormat.mFramesPerPacket;
    audioFormat.mFormatFlags      = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;
    bufferNumPackets = 2048;  // must be power of 2 for FFT!
    bufferByteSize = [self byteSizeForNumPackets:bufferNumPackets];
}
// I suspect the duplicate buffers arrive here:
static void recordCallback(
                       void* inUserData,
                       AudioQueueRef inAudioQueue,
                       AudioQueueBufferRef inBuffer,
                       const AudioTimeStamp* inStartTime,
                       UInt32 inNumPackets,
                       const AudioStreamPacketDescription* inPacketDesc)
{
     Recorder* recorder = (__bridge Recorder*) inUserData;
    if (inNumPackets > 0)
    {
        // append the buffer to FLAC encoder
        [recorder recordedBuffer:inBuffer->mAudioData byteSize:inBuffer->mAudioDataByteSize packetsNum:inNumPackets];
    }
    AudioQueueEnqueueBuffer(inAudioQueue, inBuffer, 0, NULL);
}

- (void)setUpRecordQueue
{
     OSStatus errorStatus = AudioQueueNewInput(
                   &audioFormat,
                   recordCallback,
                   (__bridge void *)(self),                // userData
                   CFRunLoopGetMain(),  // run loop
                   NULL,                // run loop mode
                   0,                   // flags
                   &recordQueue);
       UInt32 trueValue = true;
      AudioQueueSetProperty(recordQueue,kAudioQueueProperty_EnableLevelMetering,&trueValue,sizeof (UInt32));
}
- (void)setUpRecordQueueBuffers
{
    for (int t = 0; t < NUMBER_AUDIO_DATA_BUFFERS; ++t)
    {
         OSStatus errorStatus = AudioQueueAllocateBuffer(
                             recordQueue,
                             bufferByteSize,
                             &recordQueueBuffers[t]);
    }
}
- (void)primeRecordQueueBuffers
{
    for (int t = 0; t < NUMBER_AUDIO_DATA_BUFFERS; ++t)
    {
        OSStatus errorStatus = AudioQueueEnqueueBuffer(
                            recordQueue,
                            recordQueueBuffers[t],
                            0,
                            NULL);
    }
}

Answer 1

原来有一个罕见的bug允许多个录音几乎同时开始-所以两个录音并行发生，但将音频缓冲区发送到相同的回调，使失真的重复缓冲区在编码的录音…