ios - 如何从 AudioQueueBufferRef 获取 CMSampleBufferRef

Question

我正在使用一个专为 iPhone 直播而设计的私有(private)图书馆。 在每次记录每一帧时，它都会调用一个委托(delegate)函数

void MyAQInputCallback(void *inUserData, 
                              AudioQueueRef inQueue,
                              AudioQueueBufferRef inBuffer,
                              const AudioTimeStamp *inStartTime,
                              UInt32 inNumPackets,
                              const AudioStreamPacketDescription *inPacketDesc);

Now how I can append this inBuffer to my AVAssetWriterInput as usual:

[self.audioWriterInput appendSampleBuffer:sampleBuffer];

我想也许可以将 AudioQueueBufferRef 转换为 CMSampleBufferRef ？

谢谢。

Answer 1

我不认为两年后您仍在寻找解决方案，但以防万一有人处于类似情况并发现这个问题(就像我一样)，这是我的解决方案。

我的音频队列回调函数调用下面的 appendAudioBuffer 函数，并向其传递 AudioQueueBufferRef 及其长度 (mAudioDataByteSize)。

void appendAudioBuffer(void* pBuffer, long pLength)
{      
    // CMSampleBuffers require a CMBlockBuffer to hold the media data; we
    // create a blockBuffer here from the AudioQueueBuffer's data.

    CMBlockBufferRef blockBuffer;
    OSStatus status = CMBlockBufferCreateWithMemoryBlock(kCFAllocatorDefault,
                                                 pBuffer,
                                                 pLength,
                                                 kCFAllocatorNull,
                                                 NULL,
                                                 0,
                                                 pLength,
                                                 kCMBlockBufferAssureMemoryNowFlag,
                                                 &blockBuffer);

    // Timestamp of current sample
    CFAbsoluteTime currentTime = CFAbsoluteTimeGetCurrent();
    CFTimeInterval elapsedTime = currentTime - mStartTime;
    CMTime timeStamp = CMTimeMake(elapsedTime * mTimeScale, mTimeScale);

    // Number of samples in the buffer
    long nSamples = pLength / mWaveRecorder->audioFormat()->mBytesPerFrame;

    CMSampleBufferRef sampleBuffer;
    OSStatus err = CMAudioSampleBufferCreateWithPacketDescriptions(kCFAllocatorDefault,
                                                                   blockBuffer,
                                                                   true,
                                                                   NULL,
                                                                   NULL,
                                                                   mAudioFormatDescription, 
                                                                   nSamples,
                                                                   timeStamp, 
                                                                   NULL,
                                                                   &sampleBuffer);
    // Add the audio sample to the asset writer input
    if ([mAudioWriterInput isReadyForMoreMediaData]) {
        if(![mAudioWriterInput appendSampleBuffer:sampleBuffer])
            // print an error
    }
    else 
        // either do nothing and just print an error, or queue the CMSampleBuffer 
        // somewhere and add it later, when the AVAssetWriterInput is ready


    CFRelease(sampleBuffer);
    CFRelease(blockBuffer);

}

请注意，当我调用 appendAudioBuffer 时，声音并未被压缩；音频格式被指定为 LPCM(这就是为什么我不使用数据包描述符，因为 LPCM 没有数据包描述符)。 AVAssetWriterInput 处理压缩。 我最初尝试将 AAC 数据传递给 AVAssetWriter，但这导致了太多的复杂性，我无法让它工作。