Question

我正试图通过使用以下代码从iPhone的麦克风获取音频输入：

@property (nonatomic) AudioUnit rioUnit;
@property (nonatomic) CAStreamBasicDescription outputCASBD;

(...)

// set our required format - LPCM non-interleaved 32 bit floating point
CAStreamBasicDescription outFormat = CAStreamBasicDescription(44100, // sample rate
                                                              kAudioFormatLinearPCM, // format id
                                                              4, // bytes per packet
                                                              1, // frames per packet
                                                              4, // bytes per frame
                                                              1, // channels per frame
                                                              32, // bits per channel
                                                            kAudioFormatFlagIsFloat | kAudioFormatFlagIsNonInterleaved);

try {
    // Open the output unit
    AudioComponentDescription desc;
    desc.componentType = kAudioUnitType_Output;
    desc.componentSubType = kAudioUnitSubType_RemoteIO;
    desc.componentManufacturer = kAudioUnitManufacturer_Apple;
    desc.componentFlags = 0;
    desc.componentFlagsMask = 0;

    AudioComponent comp = AudioComponentFindNext(NULL, &desc);

    AudioComponentInstanceNew(comp, &_rioUnit);

    UInt32 one = 1;
    XThrowIfError(AudioUnitSetProperty(_rioUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, 1, &one, sizeof(one)), "couldn't enable input on the remote I/O unit");

    AURenderCallbackStruct callbackStruct;
    callbackStruct.inputProc = renderInput;
    callbackStruct.inputProcRefCon = (__bridge void*)self;
    XThrowIfError(AudioUnitSetProperty(_rioUnit, kAudioOutputUnitProperty_SetInputCallback, kAudioUnitScope_Global, 0, &callbackStruct, sizeof(callbackStruct)), "couldn't set remote i/o render callback");

    XThrowIfError(AudioUnitSetProperty(_rioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &outFormat, sizeof(outFormat)), "couldn't set the remote I/O unit's output client format");
    XThrowIfError(AudioUnitSetProperty(_rioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 1, &outFormat, sizeof(outFormat)), "couldn't set the remote I/O unit's input client format");

    XThrowIfError(AudioUnitInitialize(_rioUnit), "couldn't initialize the remote I/O unit");
    XThrowIfError(AudioOutputUnitStart(_rioUnit), "couldn't start the remote I/O unit");
}
catch (CAXException &e) {
    char buf[256];
    fprintf(stderr, "Error: %s (%s)\n", e.mOperation, e.FormatError(buf));
}
catch (...) {
    fprintf(stderr, "An unknown error occurred\n");
}

// Allocate our own buffers (1 channel, 16 bits per sample, thus 16 bits per frame, thus 2 bytes per frame).
// Practice learns the buffers used contain 512 frames, if this changes it will be fixed in processAudio.
// will need float for accellerate fft (input is 16 bit signed integer) so make space...
_tempBuffer.mNumberChannels = outFormat.mChannelsPerFrame;
_tempBuffer.mDataByteSize = 512 * outFormat.mBytesPerFrame * 2;
_tempBuffer.mData = malloc( self.tempBuffer.mDataByteSize );

一切都很好，直到我想停止听麦克风输入。

我这样做：

    AudioOutputUnitStop(_rioUnit);
    AudioUnitUninitialize(_rioUnit);
    AudioComponentInstanceDispose(_rioUnit);
    _rioUnit = nil;

但是我在为kAudioOutputUnitProperty_SetInputCallback定义的回调函数中收到错误。

错误是：AURemoteIO::IOThread (14): EXC_BAD_ACCESS (code=1, address=0x8000000c)

在我看来，AudioUnit的InputCallback仍然被调用，即使我正在停止它，对其实例进行单元化和处置。

为什么会发生这种情况？如何阻止在我停止，整理和处理其实例后调用InputCallback？

Answer 1

首先，确保_rioUnit在停止时确实具有与开始时相同的值。

在另一个异步线程中调用音频输入回调。因此，在未初始化或处置音频单元或任何其他所需的数据结构之前，您可能需要等待该线程也停止（通常在少于2个音频缓冲持续时间内发生，因此这可能是等待时间的合理时间）

Answer 2

问题在于这一行：

_rioUnit = nil; // causes EXC_BAD_ACCESS error

将nil更改为NULL解决了这个问题：

_rioUnit = NULL; // works smoothly

我从这篇文章中得到了这个想法： http://teragonaudio.com/article/How-to-do-realtime-recording-with-effect-processing-on-iOS.html

此外，this answer概述了nil中NULL与Objective-C之间的差异。

停止AudioUnit录制后出错

2 个答案: