AudioUnit inputCallback与AudioUnitRender ->不匹配audioBufferList.mBuffers[0].mDataByteSize != inNumberFrames

Question

我们使用AudioUnits输入回调来处理传入缓冲区。音频单元的设置主要是从

https://github.com/robovm/apple-ios-samples/blob/master/aurioTouch/Classes/AudioController.mm

我在音频回传中增加了一些理智检查。看上去像这样

/// The audio input callback
static OSStatus audioInputCallback(void __unused *inRefCon,
                                   AudioUnitRenderActionFlags *ioActionFlags,
                                   const AudioTimeStamp *inTimeStamp,
                                   UInt32  __unused inBusNumber,
                                   UInt32 inNumberFrames,
                                   AudioBufferList __unused *ioData)
{
    OSStatus err = noErr;
    if(!*callbackData.audioChainIsBeingReconstructed)
    {
        // we are calling AudioUnitRender on the input bus of AURemoteIO
        // this will store the audio data captured by the microphone in cd.audioBufferList
        err = AudioUnitRender(callbackData.audioUnit, ioActionFlags, inTimeStamp, kInputBus, inNumberFrames, &callbackData.audioBufferList);

        // check if the sample count is set correctly
        assert(callbackData.audioBufferList.mBuffers[0].mDataByteSize == inNumberFrames * sizeof(float));
        // Assert that we only received one buffer
        assert(callbackData.audioBufferList.mNumberBuffers == 1);

        // Copy buffer
        TPCircularBufferCopyAudioBufferList(callbackData.buffer, &callbackData.audioBufferList, inTimeStamp, kTPCircularBufferCopyAll, NULL);

    }
    return err;
}

现在，assert(callbackData.audioBufferList.mBuffers[0].mDataByteSize == inNumberFrames * sizeof(float));语句有时会失败，因为缓冲区是不一样的。

，有人能解释一下这个现象吗？

Answer 1

这是iOS上的正常行为。iOS音频单元回调可以更改缓冲区大小中提供的帧数，使其不同于原始缓冲区大小。当操作系统状态发生变化时，或者当音频硬件状态发生变化时，或者当可用的硬件格式与您的音频格式请求不完全匹配时，就会发生这种情况。

因此，必须编写所有Audio回调，以处理来自请求值或前一个回调值的可变数量的inNumberFrames。