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我正在制作一个基于 CoreAudio 的 FLAC 播放器，但在使用 AudioQueues 时遇到了一个顽皮的问题。我正在像这样初始化我的东西（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);

44.1 kHz 的 16 位立体声 PCM，非常基本的设置。kNumberBuffers 为 3，每个缓冲区为 0x10000 字节。我用这些回调填充缓冲区：

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，当队列请求新缓冲区时，我从 FLAC__stream_decoder 填充缓冲区，然后将其加入队列。就像其他人会做的那样。当 libFLAC 告诉我已到达文件末尾时，我告诉 AudioQueue 异步停止，直到它消耗完所有缓冲区的内容。但是，播放不会一直播放到最后，而是会提前一点点停止。如果我删除这一行：

AudioQueueStop(self->_audioQueue, false);

一切正常；音频端到端播放，尽管我的队列一直运行到时间结束。如果我将该行更改为：

AudioQueueStop(self->_audioQueue, true);

然后播放立即/同步停止，正如您从 Apple 的文档中所期望的那样：

如果传递 true，则立即停止（即同步）。如果您传递 false，该函数将立即返回，但音频队列不会停止，直到其排队的缓冲区被播放或录制（即，停止异步发生）。根据需要调用音频队列回调，直到队列实际停止。

我的问题是： - 我做错了什么吗？- 我怎样才能播放我的音频直到结束，并适当地关闭队列？

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1 回答 1

0

当然，在与这些东西斗争了几个小时之后，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。所以现在我像这样喂队列，一切都像魅力一样：

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);
    }
}
于 2013-10-27T23:00:09.503 回答