如何在iOS上使用AudioUnit.Framework配置框架

Question

我有一个音频应用程序，我需要捕捉麦克风样本编码到mp3与ffmpeg

首先配置音频：

/**  
     * We need to specifie our format on which we want to work.
     * We use Linear PCM cause its uncompressed and we work on raw data.
     * for more informations check.
     * 
     * We want 16 bits, 2 bytes (short bytes) per packet/frames at 8khz 
     */
    AudioStreamBasicDescription audioFormat;
    audioFormat.mSampleRate         = SAMPLE_RATE;
    audioFormat.mFormatID           = kAudioFormatLinearPCM;
    audioFormat.mFormatFlags        = kAudioFormatFlagIsPacked | kAudioFormatFlagIsSignedInteger;
    audioFormat.mFramesPerPacket    = 1;
    audioFormat.mChannelsPerFrame   = 1;
    audioFormat.mBitsPerChannel     = audioFormat.mChannelsPerFrame*sizeof(SInt16)*8;
    audioFormat.mBytesPerPacket     = audioFormat.mChannelsPerFrame*sizeof(SInt16);
    audioFormat.mBytesPerFrame      = audioFormat.mChannelsPerFrame*sizeof(SInt16);

static OSStatus recordingCallback(void *inRefCon, 
                                  AudioUnitRenderActionFlags *ioActionFlags, 
                                  const AudioTimeStamp *inTimeStamp, 
                                  UInt32 inBusNumber, 
                                  UInt32 inNumberFrames, 
                                  AudioBufferList *ioData) 
{
    NSLog(@"Log record: %lu", inBusNumber);
    NSLog(@"Log record: %lu", inNumberFrames);
    NSLog(@"Log record: %lu", (UInt32)inTimeStamp);

    // the data gets rendered here
    AudioBuffer buffer;

    // a variable where we check the status
    OSStatus status;

    /**
     This is the reference to the object who owns the callback.
     */
    AudioProcessor *audioProcessor = (__bridge AudioProcessor*) inRefCon;

    /**
     on this point we define the number of channels, which is mono
     for the iphone. the number of frames is usally 512 or 1024.
     */
    buffer.mDataByteSize = inNumberFrames * sizeof(SInt16); // sample size
    buffer.mNumberChannels = 1; // one channel

    buffer.mData = malloc( inNumberFrames * sizeof(SInt16) ); // buffer size

    // we put our buffer into a bufferlist array for rendering
    AudioBufferList bufferList;
    bufferList.mNumberBuffers = 1;
    bufferList.mBuffers[0] = buffer;

    // render input and check for error
    status = AudioUnitRender([audioProcessor audioUnit], ioActionFlags, inTimeStamp, inBusNumber, inNumberFrames, &bufferList);
    [audioProcessor hasError:status:__FILE__:__LINE__];

    // process the bufferlist in the audio processor
    [audioProcessor processBuffer:&bufferList];

    // clean up the buffer
    free(bufferList.mBuffers[0].mData);


    //NSLog(@"RECORD");
    return noErr;
}

Answer 1

您可以使用属性KAudiounitProperty_MaximumFramesPerslice配置AudioUnit将使用的每片帧数。然而，我认为在您的情况下最好的解决方案是将传入的音频缓冲到环形缓冲区，然后通知您的编码器音频可用。因为你是转码到MP3，我不知道实时在这种情况下意味着什么。