ios - 应该如何在 AVAudioEngine 图中配置 AUMatrixMixer？

Question

我完全坚持这一点，非常感谢任何帮助...

我在 AVAudioEngine 图表中实现了一个 AUMatrixMixer，但我听不到任何声音。如果我将 AUMatrixMixer 换成 AUMultiChannelMixer，我就能听到声音。我在直接上游节点 (AUHighPassFilter) 上安装了一个分路器，我可以看到音频被 AUMatrixMixer 提取。如果我将水龙头移到 AUMatrixMixer 的输出端，我可以看到从下一个下游节点 - AVAudioEngine 主混音器节点 - 拉取数据，但它完全没有声音......

关于 AUMatrixMixers 的评论不多，所以它可能是一些我不知道的神奇设置。作为引用来源，我收到了一封来自 Apple 技术支持的电子邮件，其中包含以下关键观察结果:

“...要在您的 AVAudioEngine 设置中使用 Matrix-Mixer，您需要使用 +instantiateWithComponentDescription:options:completionHandler: API 创建一个 AVAudioUnit，在此处找到 AVAudioUnit:

• AVAudioUnit 类引用 https://developer.apple.com/reference/avfoundation/avaudiounit

由于 AVAudioUnit 是 AVAudioNode 的子类，因此您可以在 AVAudioEngine 设置中使用利用 Matrix-Mixer 的 AVAudioUnit。您将能够进行类似于以下的设置:

AVAudioPlayerNode -> AVAudioUnit(配置了一个矩阵混音器音频单元来分割你的 channel ) -> 主混音器(你会为多路由 channel 映射配置) -> 输出...”

所以它应该可以工作。我也分析了Apple提供的示例代码:

(MatrixMixerTest https://developer.apple.com/library/mac/samplecode/MatrixMixerTest/Introduction/Intro.html ) - 这不是我想要做的，但我看不出 API 等的使用有什么不同。

创建 AUMatrixMixer(一个输入总线，两个输出总线)的代码:

private func setupMatrixMixer() {
    AVAudioUnit.instantiate(with: matrixMixerDescr, options: [.loadOutOfProcess], completionHandler: {(audioUnit, auError) in
        if let au = audioUnit {
            self.matrixMixer = au
            var error:OSStatus = noErr
            var numInputBuses:UInt32 = 1
            var numOutputBuses:UInt32 = 2
            // Input bus config
            error = AudioUnitSetProperty(self.matrixMixer.audioUnit,
                                    AudioUnitPropertyID(kAudioUnitProperty_ElementCount),
                                    AudioUnitScope(kAudioUnitScope_Input),
                                    0,
                                    &numInputBuses,
                                    UInt32(MemoryLayout<UInt32>.size))
            if error != noErr {
                assert(true, "ERROR: Setting matrix mixer number of input buses")
                return
            }
            // Output bus config
            error = AudioUnitSetProperty(self.matrixMixer.audioUnit,
                                         AudioUnitPropertyID(kAudioUnitProperty_ElementCount),
                                         AudioUnitScope(kAudioUnitScope_Output),
                                         0,
                                         &numOutputBuses,
                                         UInt32(MemoryLayout<UInt32>.size))
            if error != noErr {
                assert(true, "ERROR: Setting matrix mixer number of output buses")
                return
            }
        }
        else { trace(level: .skim, items: "ERROR: failed to create matrix mixer. Error code: \(String(describing: auError))")}
    } )
}

图形创建:

private func makeEngineConnections() {
    // Get the engine's optional singleton main mixer node
    let output = engine.mainMixerNode
    // Connect nodes
    engine.connect(player, to: timePitch, fromBus: 0, toBus: 0, format: audioFormat)
    engine.connect(timePitch, to: lowPassFilter, fromBus: 0, toBus: 0, format: audioFormat)
    engine.connect(lowPassFilter, to: highPassFilter, fromBus: 0, toBus: 0, format: audioFormat)
    engine.connect(highPassFilter, to: matrixMixer, fromBus: 0, toBus: 0, format: audioFormat)
    engine.connect(matrixMixer, to: output, fromBus: 0, toBus: 0, format: audioFormat)
    engine.connect(matrixMixer, to: output, fromBus: 1, toBus: 1, format: audioFormat)
}

设置后引擎图的转储:

________ 图描述 ________AVAudioEngineGraph 0x1701c6450:初始化=1，运行=1，节点数=8

 ******** output chain ********

 node 0x1700a9960 {'auou' 'rioc' 'appl'}, 'I'
     inputs = 1
         (bus0) <- (bus0) 0x1740ee180, {'aumx' 'mcmx' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]

 node 0x1740ee180 {'aumx' 'mcmx' 'appl'}, 'I'
     inputs = 2
         (bus0) <- (bus0) 0x1700f0200, {'aumx' 'mxmx' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]
         (bus1) <- (bus1) 0x1700f0200, {'aumx' 'mxmx' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]
     outputs = 1
         (bus0) -> (bus0) 0x1700a9960, {'auou' 'rioc' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]

 node 0x1700f0200 {'aumx' 'mxmx' 'appl'}, 'I'
     inputs = 1
         (bus0) <- (bus0) 0x1740ee100, {'aufx' 'hpas' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]
     outputs = 2
         (bus0) -> (bus0) 0x1740ee180, {'aumx' 'mcmx' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]
         (bus1) -> (bus1) 0x1740ee180, {'aumx' 'mcmx' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]

 node 0x1740ee100 {'aufx' 'hpas' 'appl'}, 'I'
     inputs = 1
         (bus0) <- (bus0) 0x1740ee700, {'aufx' 'lpas' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]
     outputs = 1
         (bus0) -> (bus0) 0x1700f0200, {'aumx' 'mxmx' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]

 node 0x1740ee700 {'aufx' 'lpas' 'appl'}, 'I'
     inputs = 1
         (bus0) <- (bus0) 0x1740ee480, {'aufc' 'nutp' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]
     outputs = 1
         (bus0) -> (bus0) 0x1740ee100, {'aufx' 'hpas' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]

 node 0x1740ee480 {'aufc' 'nutp' 'appl'}, 'I'
     inputs = 1
         (bus0) <- (bus0) 0x174198fc0, {'augn' 'sspl' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]
     outputs = 1
         (bus0) -> (bus0) 0x1740ee700, {'aufx' 'lpas' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]

 node 0x174198fc0 {'augn' 'sspl' 'appl'}, 'I'
     outputs = 1
         (bus0) -> (bus0) 0x1740ee480, {'aufc' 'nutp' 'appl'}, [ 2 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]

 ******** other nodes ********

 node 0x1700ef000 {'aumx' 'mcmx' 'appl'}, 'U'

---

AUMatrixMixer 内部的设置有点乏味。总结:

• 启用输入总线
• 在每个输入 channel (其中 2 个)上设置音量
• 启用输出总线(实际上，这是多余的，因为它们都是永久启用的)
• 在每个输出 channel (其中 4 个)上设置音量
• 在每个交叉点上设置音量(我现在将所有设置为 1(最大音量))- 其中 8 个
• 设置混音器的全局音量(1 个设置)

这是执行上述操作后的内部状态转储:

Matrix dimensions: [2, 4]
Input element count: 1
Input channel 0 volume: 1.0
Input channel 1 volume: 1.0
Output element count: 2
Output channel 0 volume: 1.0
Output channel 1 volume: 1.0
Output channel 2 volume: 1.0
Output channel 3 volume: 1.0
Crosspoint volumes: [1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0]
Input 0 enabled parameter: 1.0
Output 0 enabled parameter: 1.0
Output 1 enabled parameter: 1.0

如您所见，一切都已启用，所有音量都设置为最大但没有输出声音....

如上所述，通过点击不同节点的输出，我已经验证了良好的数据正在从高通滤波器移动到矩阵混音器，但在矩阵混音器和主混音器之间移动的是静音混合器节点。

有谁知道我还需要做些什么才能从中获得声音？

问候，空调

Answer 1

几个星期以来，我一直面临同样的情况。刚才，我正在写一段示例代码来询问 Apple Code-Level 支持。我在准备发送时测试了它，假设它不会像往常一样工作，但令人惊讶的是它确实有效!我认为，像 AUGraph 一样，必须有一些特定的顺序来设置流格式、连接节点等，这是它正常工作所必需的。 (而且，与 AUGraph 一样，文档并没有准确解释该顺序是什么。)所以我不太确定这次我做了什么不同的事情，但至少它现在对我有用。

所以这是一个成功使用带有 AVAudioEngine 的矩阵混音器的准系统示例:

NSURL *audioURL = /*an audio URL*/
AVAudioFile *file = [[AVAudioFile alloc] initForReading:audioURL error:nil];
AVAudioPlayerNode *audioPlayer = [[AVAudioPlayerNode alloc] init];

_engine = [[AVAudioEngine alloc] init];

[_engine attachNode:audioPlayer];

AudioComponentDescription mixerDesc;
mixerDesc.componentType = kAudioUnitType_Mixer;
mixerDesc.componentSubType = kAudioUnitSubType_MatrixMixer;
mixerDesc.componentManufacturer = kAudioUnitManufacturer_Apple;
mixerDesc.componentFlags = kAudioComponentFlag_SandboxSafe;

[AVAudioUnit instantiateWithComponentDescription:mixerDesc options:kAudioComponentInstantiation_LoadInProcess completionHandler:^(__kindof AVAudioUnit * _Nullable mixerUnit, NSError * _Nullable error) {

    [_engine attachNode:mixerUnit];

    /*Give the mixer one input bus and one output bus*/
    UInt32 inBuses = 1;
    UInt32 outBuses = 1;
    AudioUnitSetProperty(mixerUnit.audioUnit, kAudioUnitProperty_ElementCount, kAudioUnitScope_Input, 0, &inBuses, sizeof(UInt32));
    AudioUnitSetProperty(mixerUnit.audioUnit, kAudioUnitProperty_ElementCount, kAudioUnitScope_Output, 0, &outBuses, sizeof(UInt32));

    /*Set the mixer's input format to have 2 channels*/
    UInt32 inputChannels = 2;
    AudioStreamBasicDescription mixerFormatIn;
    UInt32 size;
    AudioUnitGetProperty(mixerUnit.audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &mixerFormatIn, &size);
    mixerFormatIn.mChannelsPerFrame = inputChannels;
    AudioUnitSetProperty(mixerUnit.audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, 0, &mixerFormatIn, size);

    /*Set the mixer's output format to have 2 channels*/
    UInt32 outputChannels = 2;
    AudioStreamBasicDescription mixerFormatOut;
    AudioUnitGetProperty(mixerUnit.audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 0, &mixerFormatOut, &size);
    mixerFormatOut.mChannelsPerFrame = outputChannels;

    AudioUnitSetProperty(mixerUnit.audioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 0, &mixerFormatOut, size);

    /*Connect the nodes*/
    [_engine connect:audioPlayer to:mixerUnit format:nil];
    [_engine connect:mixerUnit to:_engine.outputNode format:nil];

    /*Start the engine*/
    [_engine startAndReturnError:nil];

    /*Play the audio file*/
    [audioPlayer scheduleFile:file atTime:nil completionHandler:nil];
    [audioPlayer play];

    /*Set all matrix volumes to 1*/

    /*Set the master volume*/
    AudioUnitSetParameter(mixerUnit.audioUnit, kMatrixMixerParam_Volume, kAudioUnitScope_Global, 0xFFFFFFFF, 1.0, 0);

    for(UInt32 i = 0; i < inputChannels; i++) {

        /*Set input volumes*/
        AudioUnitSetParameter(mixerUnit.audioUnit, kMatrixMixerParam_Volume, kAudioUnitScope_Input, i, 1.0, 0);

        for(UInt32 j = 0; j < outputChannels; j++) {
            /*Set output volumes (only one outer iteration necessary)*/
            if(i == 0) {
                AudioUnitSetParameter(mixerUnit.audioUnit, kMatrixMixerParam_Volume, kAudioUnitScope_Output, j, 1.0, 0);
            }

            /*Set cross point volumes - 1.0 for corresponding
             inputs/outputs, otherwise 0.0*/
            UInt32 crossPoint = (i << 16) | (j & 0x0000FFFF);
            AudioUnitSetParameter(mixerUnit.audioUnit, kMatrixMixerParam_Volume, kAudioUnitScope_Global, crossPoint, (i == j) ? 1.0 : 0.0, 0);
        }

    }

    /*If you want to verify it's working, try something like this to silence only one channel of audio
    AudioUnitSetParameter(mixerUnit.audioUnit, kMatrixMixerParam_Volume, kAudioUnitScope_Output, 0, 0.0, 0);
    */
}];