CoreAudio AudioQueue停止问题

Question

我正在制作一个基于CoreAudio的FLAC播放器，并与AudioQueues遇到了一个顽皮的问题。我正在像这样初始化我的内容(以下划线开头的变量是实例变量)：

    _flacDecoder = FLAC__stream_decoder_new();

    AudioStreamBasicDescription asbd = {
        .mFormatID = kAudioFormatLinearPCM,
        .mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked,
        .mSampleRate = 44100,
        .mChannelsPerFrame = 2,
        .mBitsPerChannel = 16,
        .mBytesPerPacket = 4,
        .mFramesPerPacket = 1,
        .mBytesPerFrame = 4,
        .mReserved = 0
    };

    AudioQueueNewOutput(&asbd, HandleOutputBuffer, (__bridge void *)(self), CFRunLoopGetCurrent(), kCFRunLoopDefaultMode, 0, &_audioQueue);

    for (int i = 0; i < kNumberBuffers; ++i) {
        AudioQueueAllocateBuffer(_audioQueue, 0x10000, &_audioQueueBuffers[i]);
    }

    AudioQueueSetParameter(_audioQueue, kAudioQueueParam_Volume, 1.0);

16位立体声PCM在44.1 kHz，相当基本的设置。kNumberBuffers为3，每个缓冲区为0x10000字节。我用以下回调填充缓冲区：

static void HandleOutputBuffer(void *inUserData, AudioQueueRef inAQ, AudioQueueBufferRef inBuffer){

    FLACPlayer * self = (__bridge FLACPlayer*)inUserData;

    UInt32 largestBlockSizeInBytes = self->_currentStreamInfo.max_blocksize * self->_currentStreamInfo.channels * self->_currentStreamInfo.bits_per_sample/8;

    inBuffer->mAudioDataByteSize = 0;
    self->_buffer = inBuffer;

    while(inBuffer->mAudioDataByteSize <= inBuffer->mAudioDataBytesCapacity - largestBlockSizeInBytes){
        FLAC__bool result = FLAC__stream_decoder_process_single(self->_flacDecoder);
        assert(result);

        if(FLAC__stream_decoder_get_state(self->_flacDecoder) == FLAC__STREAM_DECODER_END_OF_STREAM){
            AudioQueueStop(self->_audioQueue, false);
            break;
        }
    }

    AudioQueueEnqueueBuffer(inAQ, inBuffer, 0, NULL);
}

static FLAC__StreamDecoderWriteStatus flacDecoderWriteCallback(const FLAC__StreamDecoder *decoder, const FLAC__Frame *frame, const FLAC__int32 * const buffer[], void *client_data){

    FLACPlayer * self = (__bridge FLACPlayer *)client_data;

    assert(frame->header.bits_per_sample == 16); // TODO

    int16_t * bufferWritePosition = (int16_t*)((uint8_t*)self->_buffer->mAudioData + self->_buffer->mAudioDataByteSize);
    for(int i = 0; i < frame->header.blocksize; i++){
        for(int j = 0; j < frame->header.channels; j++){
            *bufferWritePosition = (int16_t)buffer[j][i];
            bufferWritePosition++;
        }
    }

    int totalFramePayloadInBytes = frame->header.channels * frame->header.blocksize * frame->header.bits_per_sample/8;
    self->_buffer->mAudioDataByteSize += totalFramePayloadInBytes;

    return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
}

static void flacDecoderMetadataCallback(const FLAC__StreamDecoder *decoder, const FLAC__StreamMetadata *metadata, void *client_data){

    FLACPlayer * self = (__bridge FLACPlayer*) client_data;

    if(metadata->type == FLAC__METADATA_TYPE_STREAMINFO){
        self->_currentStreamInfo = metadata->data.stream_info;
    }
}

基本上，当队列请求一个新缓冲区时，我从FLAC__stream_decoder中填充缓冲区，然后对它进行排队。就像其他人一样。当libFLAC告诉我我已经到达文件的末尾时，我告诉AudioQueue异步停止，直到它已经消耗了所有缓冲区的内容。然而，回放并没有一直播放到最后，而是在它应该播放之前停止了一点点。如果我删除这一行：

AudioQueueStop(self->_audioQueue, false);

一切都很好；音频点对点播放，尽管我的队列一直在运行到时间的尽头。如果我把这一行改为：

AudioQueueStop(self->_audioQueue, true);

然后，播放会立即/同步停止，正如您从Apple文档中所期望的那样：

如果传递true，则立即停止(即同步)。如果传递false，函数将立即返回，但音频队列在播放或记录其排队缓冲区之前不会停止(也就是说，停止是异步发生的)。在队列实际停止之前，将根据需要调用音频队列回调。

我的问题是：-我做错什么了吗？-我怎么才能播放我的音频直到结束，并适当地关闭队列？

Answer 1

当然，经过几个小时的努力，我在发布这个问题几分钟后找到了解决方案。问题是，AudioQueue不关心在调用AudioQueueStop(.，false)后排队的缓冲区。所以现在我就像这样排队，一切都很有魅力：

static void HandleOutputBuffer(void *inUserData, AudioQueueRef inAQ, AudioQueueBufferRef inBuffer){

    FLACPlayer * self = (__bridge FLACPlayer*)inUserData;

    UInt32 largestBlockSizeInBytes = self->_currentStreamInfo.max_blocksize * self->_currentStreamInfo.channels * self->_currentStreamInfo.bits_per_sample/8;

    inBuffer->mAudioDataByteSize = 0;
    self->_buffer = inBuffer;

    bool shouldStop = false;

    while(inBuffer->mAudioDataByteSize <= inBuffer->mAudioDataBytesCapacity - largestBlockSizeInBytes){
        FLAC__bool result = FLAC__stream_decoder_process_single(self->_flacDecoder);
        assert(result);

        if(FLAC__stream_decoder_get_state(self->_flacDecoder) == FLAC__STREAM_DECODER_END_OF_STREAM){
            shouldStop = true;
            break;
        }
    }

    AudioQueueEnqueueBuffer(inAQ, inBuffer, 0, NULL);
    if(shouldStop){
        AudioQueueStop(self->_audioQueue, false);
    }
}