How to get CMSampleBufferRef from AudioQueueBufferRef

问题

I am using a private library which was made for live broadcasting from iPhone. In every time of recording each frame it call a delegate function

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];

I think maybe convert AudioQueueBufferRef to CMSampleBufferRef somehow?

Thank you.

回答1:

I don't suppose you are still looking for a solution two years later, but just in case someone is in a similar situation and finds this question (as I did), here is my solution.

My Audio Queue callback function calls the appendAudioBuffer function below, passing it the AudioQueueBufferRef and its length (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);

}

Note that the sound is not compressed when I call appendAudioBuffer; the audio format is specified as LPCM (which is why I don't use packet descriptors, as there are none for LPCM). The AVAssetWriterInput handles the compression. I originally tried to pass AAC data to the AVAssetWriter, but this led to way too much complication and I was unable to get it to work.

来源：https://stackoverflow.com/questions/20212320/how-to-get-cmsamplebufferref-from-audioqueuebufferref