Question

我正在制作基于CoreAudio的FLAC播放器，并在AudioQueues中遇到了一个顽皮的问题。我正在初始化这样的东西（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);

16位立体声PCM，44.1 kHz，非常基本的设置。 kNumberBuffers为3，每个缓冲区为0x10000字节。我使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，然后我将其排队。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，直到它消耗了所有缓冲区＆＃39;内容。然而，播放不是播放结束，而是在应该播放之前停止播放。如果我删除此行：

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);

然后播放会立即/同步停止，正如您对Apple的文档所期望的那样：

如果你通过了，立即停止（也就是说，同步）。如果传递false，则函数立即返回，但是音频队列在播放排队的缓冲区之前不会停止或记录（即停止异步发生）。音频队列必要时调用回调，直到队列实际停止为止。

我的问题是： - 我做错了吗？ - 如何播放音频直到结束，并正确关闭队列？

Answer 1

当然，经过几个小时的努力，我在发布这个问题后找到了解决方案...... 问题是AudioQueue不关心在调用 AudioQueueStop（...，false）之后排队的缓冲区。所以现在我正在这样排队，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); } }

CoreAudio AudioQueue停止问题

1 个答案: