c++ - 从 AudioInputIOProc 创建 CMSampleBufferRef

Question

我有一个 AudioInputIOProc，我正在从中获取一个 AudioBufferList。我需要将此 AudioBufferList 转换为 CMSampleBufferRef。

这是我到目前为止编写的代码:

- (void)handleAudioSamples:(const AudioBufferList*)samples numSamples:(UInt32)numSamples hostTime:(UInt64)hostTime {
// Create a CMSampleBufferRef from the list of samples, which we'll own

  AudioStreamBasicDescription monoStreamFormat;
  memset(&monoStreamFormat, 0, sizeof(monoStreamFormat));
  monoStreamFormat.mSampleRate = 44100;
  monoStreamFormat.mFormatID = kAudioFormatMPEG4AAC;
  monoStreamFormat.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagsNativeEndian | kAudioFormatFlagIsPacked | kAudioFormatFlagIsNonInterleaved;
  monoStreamFormat.mBytesPerPacket = 4;
  monoStreamFormat.mFramesPerPacket = 1;
  monoStreamFormat.mBytesPerFrame = 4;
  monoStreamFormat.mChannelsPerFrame = 2;
  monoStreamFormat.mBitsPerChannel = 16;

  CMFormatDescriptionRef format = NULL;
  OSStatus status = CMAudioFormatDescriptionCreate(kCFAllocatorDefault, &monoStreamFormat, 0, NULL, 0, NULL, NULL, &format);
  if (status != noErr) {
    // really shouldn't happen
    return;
  }

  mach_timebase_info_data_t tinfo;
  mach_timebase_info(&tinfo);

  UInt64 _hostTimeToNSFactor = (double)tinfo.numer / tinfo.denom;

  uint64_t timeNS = (uint64_t)(hostTime * _hostTimeToNSFactor);
  CMTime presentationTime = CMTimeMake(timeNS, 1000000000);
  CMSampleTimingInfo timing = { CMTimeMake(1, 44100), kCMTimeZero, kCMTimeInvalid };

  CMSampleBufferRef sampleBuffer = NULL;
  status = CMSampleBufferCreate(kCFAllocatorDefault, NULL, false, NULL, NULL, format, numSamples, 1, &timing, 0, NULL, &sampleBuffer);
  if (status != noErr) {
    // couldn't create the sample buffer
    NSLog(@"Failed to create sample buffer");
    CFRelease(format);
    return;
  }

  // add the samples to the buffer
  status = CMSampleBufferSetDataBufferFromAudioBufferList(sampleBuffer,
                                                        kCFAllocatorDefault,
                                                        kCFAllocatorDefault,
                                                        0,
                                                        samples);
  if (status != noErr) {
    NSLog(@"Failed to add samples to sample buffer");
    CFRelease(sampleBuffer);
    CFRelease(format);
    NSLog(@"Error status code: %d", status);
    return;
  }

  [self addAudioFrame:sampleBuffer];

  NSLog(@"Original sample buf size: %ld for %d samples from %d buffers, first buffer has size %d", CMSampleBufferGetTotalSampleSize(sampleBuffer), numSamples, samples->mNumberBuffers, samples->mBuffers[0].mDataByteSize);
  NSLog(@"Original sample buf has %ld samples", CMSampleBufferGetNumSamples(sampleBuffer));
}

现在，我不确定如何根据 AudioInputIOProc 的函数定义计算 numSamples:

OSStatus AudioTee::InputIOProc(AudioDeviceID inDevice, const AudioTimeStamp *inNow, const AudioBufferList *inInputData, const AudioTimeStamp *inInputTime, AudioBufferList *outOutputData, const AudioTimeStamp *inOutputTime, void *inClientData)

这个定义存在于AudioTee.cpp WavTap 中的文件。

我遇到的错误是 CMSampleBufferError_RequiredParameterMissing 错误，错误代码为 -12731，当我尝试调用 CMSampleBufferSetDataBufferFromAudioBufferList 时。

更新:

为了澄清问题，以下是我从 AudioDeviceIOProc 获取的音频数据的格式:

channel :2，采样率:44100，精度:32 位，样本编码:32 位有符号整数 PCM，字节序类型:小，反向半字节:无，反向位:无

我得到一个 AudioBufferList*，其中包含我需要转换为 CMSampleBufferRef* 的所有音频数据(30 秒视频)并添加这些样本缓冲区通过 AVAssetWriterInput 写入磁盘的视频(时长 30 秒)。

Answer 1

三个地方看起来不对:

1. 您声明格式 ID 为 kAudioFormatMPEG4AAC，但将其配置为 LPCM。所以试试

   monoStreamFormat.mFormatID = kAudioFormatLinearPCM;

   当格​​式配置为立体声时，您也可以将其称为“单声道”。

2. 为什么要使用 mach_timebase_info，它可能会在您的音频演示时间戳中留下空白？改用样本计数:

   CMTime presentationTime = CMTimeMake(numSamplesProcessed, 44100);

3. 您的 CMSampleTimingInfo 看起来不对，而且您没有使用 presentationTime。当缓冲区的持续时间可以是 numSamples 时，您可以将缓冲区的持续时间设置为 1 个样本长，并将其呈现时间设置为零，这是不正确的。这样的事情会更有意义:

   CMSampleTimingInfo timing = { CMTimeMake(numSamples, 44100), presentationTime, kCMTimeInvalid };

还有一些问题:

您的 AudioBufferList 是否具有预期的 2 个 AudioBuffers？ 你有这个的可运行版本吗？

附注我自己对此感到内疚，但在音频线程上分配内存是 considered harmful在音频开发中。