swift - 如何将包含 AAC 数据的 AudioBufferList 转换为 CMSampleBuffer

Question

我正在使用 AudioConverter转换未压缩 CMSampleBuffer通过 AVCaptureSession 被捕获至 AudioBufferList :

let status: OSStatus = AudioConverterFillComplexBuffer(
            converter,
            inputDataProc,
            Unmanaged.passUnretained(self).toOpaque(),
            &ioOutputDataPacketSize,
            outOutputData.unsafeMutablePointer,
            nil
        )

我的输出 asbd 设置如下:

AudioStreamBasicDescription
- mSampleRate : 44100.0
- mFormatID : 1633772320
- mFormatFlags : 2
- mBytesPerPacket : 0
- mFramesPerPacket : 1024
- mBytesPerFrame : 0
- mChannelsPerFrame : 1
- mBitsPerChannel : 0
- mReserved : 0

我想转换 AudioBufferList回到 CMSampleBuffer包含压缩数据，以便我可以使用 AVAssetWriter 将其写入 mp4 文件(我已经想出了如何用视频来做到这一点)，但到目前为止几乎没有。我试过咨询 this answer但在这种情况下，有 PCM 数据，它在这里似乎不可用。

我可以访问 AudioBufferList以及原始样本的presentationTimeStamp。我已经尝试了以下方法，但我不太确定如何计算 numSamples 以及这种方法是否有意义:

 func createCMSampleBuffer(_ data: UnsafeMutableAudioBufferListPointer, presentationTimeStamp: CMTime) -> CMSampleBuffer? {
    let numSamples = // not sure how to get this

    var status: OSStatus = noErr
    var sampleBuffer: CMSampleBuffer?
    var timing: CMSampleTimingInfo = CMSampleTimingInfo(
        duration: CMTime(value: CMTimeValue(numSamples), timescale: presentationTimeStamp.timescale),
        presentationTimeStamp: presentationTimeStamp,
        decodeTimeStamp: CMTime.invalid
    )

    status = CMSampleBufferCreate(
        allocator: kCFAllocatorDefault,
        dataBuffer: nil,
        dataReady: false,
        makeDataReadyCallback: nil,
        refcon: nil,
        formatDescription: formatDescription,
        sampleCount: CMItemCount(numSamples),
        sampleTimingEntryCount: 1,
        sampleTimingArray: &timing,
        sampleSizeEntryCount: 0,
        sampleSizeArray: nil,
        sampleBufferOut: &sampleBuffer
    )

    guard status == noErr else {
        return nil
    }

    status = CMSampleBufferSetDataBufferFromAudioBufferList(
        sampleBuffer!,
        blockBufferAllocator: kCFAllocatorDefault,
        blockBufferMemoryAllocator: kCFAllocatorDefault,
        flags: 0,
        bufferList: data.unsafePointer
    )

    guard status == noErr else {
        return nil
    }

    return sampleBuffer
}

最后我确实设法创建了一个 CMSampleBuffer ，但是当我尝试完成写作时，出现以下错误:

Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" UserInfo={NSUnderlyingError=0x174442ac0 {Error Domain=NSOSStatusErrorDomain Code=-12735 "(null)"}, NSLocalizedFailureReason=An unknown error occurred (-12735), NSLocalizedDescription=The operation could not be completed}

Answer 1

我可以分享一些关于这方面的研究工作，它可能会帮助你......
CMSampleBufferSetDataBufferFromAudioBufferList returned error: -12731
解决方案:- https://lists.apple.com/archives/coreaudio-api/2014/Mar/msg00008.html

或者 Converting AudioBuffer to CMSampleBuffer with accurate CMTime

可能会帮助你...:)