ios - 来自 RemoteIO : resulting . caf 的录音音高偏移较慢 + 失真

Question

所以我根据这里的一些帖子拼凑了一些录制音频的例程。我引用的帖子是 here和 here ，以及阅读他们引用的网站。

我的设置:我有一个现有的 AUGraph:(几个 AUSamplers -> Mixer -> RemoteIO)。 AUSamplers 连接到 MusicPlayer 实例中的轨道。一切正常但是 我想给它添加录音。

录音工作正常，但生成的 .caf 音高/速度移动较慢 + 音质较差。我指定的格式一定有问题吗？

有人可以观察一下并告诉我哪里设置的格式不正确吗？

编辑:这可能是立体声/单声道问题吗？我的意思是用单声道录音。

我将 RemoteIO 实例上的流格式设置为:

   AudioStreamBasicDescription audioFormat;

audioFormat.mSampleRate         = 44100.00;
audioFormat.mFormatID           = kAudioFormatLinearPCM;
audioFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
audioFormat.mFramesPerPacket    = 1;
audioFormat.mChannelsPerFrame   = 1;
audioFormat.mBitsPerChannel     = 16;
audioFormat.mBytesPerPacket     = 2;
audioFormat.mBytesPerFrame      = 2;

// Apply format
result = AudioUnitSetProperty(ioUnit, 
                              kAudioUnitProperty_StreamFormat, 
                              kAudioUnitScope_Output, 
                              kInputBus, 
                              &audioFormat, 
                              sizeof(audioFormat));

然后我从一个按钮操作创建一个 fileRef 并将一个 renderCallback 附加到 RemoteIO 实例:

- (void)startRecording
{

OSStatus result;

AudioStreamBasicDescription audioFormat;

audioFormat.mSampleRate         = 44100.00;
audioFormat.mFormatID           = kAudioFormatLinearPCM;
audioFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
audioFormat.mFramesPerPacket    = 1;
audioFormat.mChannelsPerFrame   = 1;
audioFormat.mBitsPerChannel     = 16;
audioFormat.mBytesPerPacket     = 2;
audioFormat.mBytesPerFrame      = 2;

NSArray  *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *destinationFilePath = [[NSString alloc] initWithFormat: @"%@/output.caf", documentsDirectory];
CFURLRef destinationURL = CFURLCreateWithFileSystemPath(kCFAllocatorDefault, 
                                                        (__bridge CFStringRef)destinationFilePath, 
                                                        kCFURLPOSIXPathStyle, 
                                                        false);

result = ExtAudioFileCreateWithURL(destinationURL, 
                                   kAudioFileWAVEType, 
                                   &audioFormat, 
                                   NULL, 
                                   kAudioFileFlags_EraseFile, 
                                   &extAudioFileRef);  

CFRelease(destinationURL);
NSAssert(result == noErr, @"Couldn't create file for writing");

result = ExtAudioFileSetProperty(extAudioFileRef, 
                                 kExtAudioFileProperty_ClientDataFormat, 
                                 sizeof(AudioStreamBasicDescription), 
                                 &audioFormat);

NSAssert(result == noErr, @"Couldn't create file for format");

result =  ExtAudioFileWriteAsync(extAudioFileRef, 0, NULL);
NSAssert(result == noErr, @"Couldn't initialize write buffers for audio file");   


printf("Adding render to remoteIO     \n");
result = AudioUnitAddRenderNotify(ioUnit, renderCallback, (__bridge void*)self);
if (result) {[self printErrorMessage: @"AudioUnitAddRenderNotify" withStatus: result]; return;}
 }

最后，在我的 rendercallback 中，我写出了 postRender 阶段的数据:

static OSStatus renderCallback (void *                       inRefCon,
                            AudioUnitRenderActionFlags * ioActionFlags,
                            const AudioTimeStamp *       inTimeStamp,
                            UInt32                       inBusNumber,
                            UInt32                       inNumberFrames,
                            AudioBufferList *            ioData) 
{

OSStatus result;
   if (*ioActionFlags == kAudioUnitRenderAction_PostRender){
    double timeInSeconds = inTimeStamp->mSampleTime / kSampleRate;
    printf("%fs inBusNumber: %lu inNumberFrames: %lu \n", timeInSeconds, inBusNumber, inNumberFrames);

    MusicPlayerController* THIS = (__bridge MusicPlayerController *)inRefCon;

   result =  ExtAudioFileWriteAsync(THIS->extAudioFileRef, inNumberFrames, ioData);
    if(result) printf("ExtAudioFileWriteAsync %ld \n", result);

  }

return noErr; 
}

Answer 1

好的 - 找到了一些解决这个问题的代码 - 虽然我不完全明白为什么。

我一直将 RemoteIO 输出流和 ExtFileRef 的 mBitsPerChannel 设置为 16。结果是速度变慢且声音沙哑。将 ExtFileRef mBitsPerChannel 设置为 32 并添加 kAudioFormatFlagsNativeEndian 标志可以解决问题:.caf 音频是完美的(同时将 RemoteIO 输出流设置保持原样)。

但随后也可以设置 RemoteIO 输出流设置以匹配我的新设置。所以我很困惑。只要 AudioStreamBasicDescription 设置对于 RemoteIO 实例和 ExtFileRef 是对称的，这不应该起作用吗？

无论如何...工作设置如下。

size_t bytesPerSample = sizeof (AudioUnitSampleType);

AudioStreamBasicDescription audioFormat;
audioFormat.mSampleRate= graphSampleRate;
audioFormat.mFormatID=kAudioFormatLinearPCM;
audioFormat.mFormatFlags=kAudioFormatFlagsNativeEndian|kAudioFormatFlagIsSignedInteger|kAudioFormatFlagIsPacked;
audioFormat.mBytesPerPacket=bytesPerSample;
audioFormat.mBytesPerFrame=bytesPerSample;
audioFormat.mFramesPerPacket=1;
audioFormat.mChannelsPerFrame=1;
audioFormat.mBitsPerChannel= 8 * bytesPerSample;
audioFormat.mReserved=0;