Question

我正在寻找使用MTAudioProcessingTap和多声道混音器音频单元来平移单声道信号，但我正在获得单声道输出而不是平移立体声输出。 documentation州：

“多通道混音器单元（子类型 kAudioUnitSubType_MultiChannelMixer）可以使用任意数量的单声道或立体声流并将它们组合成一个立体声输出。“

因此，单声道输出是出乎意料的。有什么方法吗？我通过完全相同的代码运行立体声信号，一切都很好：立体声输出，按预期平移。这是我点击准备回调的代码：

static void tap_PrepareCallback(MTAudioProcessingTapRef tap,
                                CMItemCount maxFrames,
                                const AudioStreamBasicDescription *processingFormat) {

    AVAudioTapProcessorContext *context = (AVAudioTapProcessorContext *)MTAudioProcessingTapGetStorage(tap);

    // Store sample rate for -setCenterFrequency:.
    context->sampleRate = processingFormat->mSampleRate;

    /* Verify processing format (this is not needed for Audio Unit, but for RMS calculation). */
    context->supportedTapProcessingFormat = true;

    if (processingFormat->mFormatID != kAudioFormatLinearPCM) {
        NSLog(@"Unsupported audio format ID for audioProcessingTap. LinearPCM only.");
        context->supportedTapProcessingFormat = false;
    }

    if (!(processingFormat->mFormatFlags & kAudioFormatFlagIsFloat)) {
        NSLog(@"Unsupported audio format flag for audioProcessingTap. Float only.");
        context->supportedTapProcessingFormat = false;
    }

    if (processingFormat->mFormatFlags & kAudioFormatFlagIsNonInterleaved) {
        context->isNonInterleaved = true;
    }


    AudioUnit audioUnit;

    AudioComponentDescription audioComponentDescription;
    audioComponentDescription.componentType = kAudioUnitType_Mixer;
    audioComponentDescription.componentSubType = kAudioUnitSubType_MultiChannelMixer;
    audioComponentDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
    audioComponentDescription.componentFlags = 0;
    audioComponentDescription.componentFlagsMask = 0;

    AudioComponent audioComponent = AudioComponentFindNext(NULL, &audioComponentDescription);
    if (audioComponent) {
        if (noErr == AudioComponentInstanceNew(audioComponent, &audioUnit)) {
            OSStatus status = noErr;

            // Set audio unit input/output stream format to processing format.
            if (noErr == status) {
                status = AudioUnitSetProperty(audioUnit,
                                              kAudioUnitProperty_StreamFormat,
                                              kAudioUnitScope_Input,
                                              0,
                                              processingFormat,
                                              sizeof(AudioStreamBasicDescription));
            }

            if (noErr == status) {
                status = AudioUnitSetProperty(audioUnit,
                                              kAudioUnitProperty_StreamFormat,
                                              kAudioUnitScope_Output,
                                              0,
                                              processingFormat,
                                              sizeof(AudioStreamBasicDescription));
            }

            // Set audio unit render callback.
            if (noErr == status) {
                AURenderCallbackStruct renderCallbackStruct;
                renderCallbackStruct.inputProc = AU_RenderCallback;
                renderCallbackStruct.inputProcRefCon = (void *)tap;
                status = AudioUnitSetProperty(audioUnit,
                                              kAudioUnitProperty_SetRenderCallback,
                                              kAudioUnitScope_Input,
                                              0,
                                              &renderCallbackStruct,
                                              sizeof(AURenderCallbackStruct));
            }

            // Set audio unit maximum frames per slice to max frames.
            if (noErr == status) {
                UInt32 maximumFramesPerSlice = (UInt32)maxFrames;
                status = AudioUnitSetProperty(audioUnit,
                                              kAudioUnitProperty_MaximumFramesPerSlice,
                                              kAudioUnitScope_Global,
                                              0,
                                              &maximumFramesPerSlice,
                                              (UInt32)sizeof(UInt32));
            }

            // Initialize audio unit.
            if (noErr == status) {
                status = AudioUnitInitialize(audioUnit);
            }

            if (noErr != status) {
                AudioComponentInstanceDispose(audioUnit);
                audioUnit = NULL;
            }
            context->audioUnit = audioUnit;
        }
    }
    NSLog(@"Tap channels: %d",processingFormat->mChannelsPerFrame); // = 1 for mono source file
}

我为输出流格式尝试了一些不同的选项，例如AVAudioFormat *outFormat = [[AVAudioFormat alloc] initStandardFormatWithSampleRate:processingFormat->mSampleRate channels:2];，但每次都会出现此错误：“客户端没有看到20个I / O周期;放弃了。”这里的代码创建了与输入格式完全相同的ASBD，除了2个通道而不是1个通道，这也给出了相同的“20个I / O周期”错误：

AudioStreamBasicDescription asbd;
asbd.mFormatID = kAudioFormatLinearPCM;
asbd.mFormatFlags = 0x29;
asbd.mSampleRate = 44100;
asbd.mBitsPerChannel = 32;
asbd.mChannelsPerFrame = 2;
asbd.mBytesPerFrame = 4;
asbd.mFramesPerPacket = 1;
asbd.mBytesPerPacket = 4;
asbd.mReserved = 0;

使用MultiChannelMixer＆amp ;;平移单声道信号MTAudioProcessingTap

0 个答案: