在Xamarin.Mac中使用AUGraph

Question

我正在尝试使以下示例在Xamarin.Mac项目中工作。 这是一个将混音器连接到默认输出的AUGraph 。 混频器有一个输入，它是一个生成正弦波形的渲染回调。

        var graph = new AUGraph();

        var output = graph.AddNode(AudioComponentDescription.CreateOutput(AudioTypeOutput.Default));

        var mixer = graph.AddNode(AudioComponentDescription.CreateMixer(AudioTypeMixer.MultiChannel));

        if (graph.TryOpen() != 0)
        {
            throw new Exception();
        }

        var mixNode = graph.GetNodeInfo(mixer);

        // configure mixer
        if (mixNode.SetElementCount(AudioUnitScopeType.Input, 1) != AudioUnitStatus.OK)
        {
            throw new Exception();
        }

        if (mixNode.SetRenderCallback(HandleRenderDelegate, AudioUnitScopeType.Global, 0) != AudioUnitStatus.OK)
        {
            throw new Exception();
        }

        var outNode = graph.GetNodeInfo(output);

        // define stream description
        var desc = new AudioStreamBasicDescription();
        desc.BitsPerChannel = 32;
        desc.BytesPerFrame = 4;
        desc.BytesPerPacket = 4;
        desc.Format = AudioFormatType.LinearPCM;
        desc.FormatFlags = AudioStreamBasicDescription.AudioFormatFlagsAudioUnitNativeFloat;
        desc.FramesPerPacket = 1;
        desc.ChannelsPerFrame = 2;
        desc.SampleRate = 44100;

        // set mixer input format
        if (mixNode.SetFormat(desc, AudioUnitScopeType.Input, 0) != AudioUnitStatus.OK)
        {
            throw new Exception();
        }

        // connect mixer's output to the output
        if (graph.ConnnectNodeInput(mixer, 0, output, 0) != AUGraphError.OK)
        {
            throw new Exception();
        }

        // set format of mixer's output
        desc = mixNode.GetAudioFormat(AudioUnitScopeType.Output);

        desc.SampleRate = 44100;

        if (outNode.SetFormat(desc, AudioUnitScopeType.Input,0) != AudioUnitStatus.OK)
        {
            throw new Exception();
        }

        if (mixNode.SetFormat(desc, AudioUnitScopeType.Output) != AudioUnitStatus.OK)
        {
            throw new Exception();
        }

        if (graph.Initialize() != AUGraphError.OK)
        {
            throw new Exception();
        }

        if (graph.Start() != AUGraphError.OK)
        {
            throw new Exception();
        }

回调：

int sample = 0;

unsafe AudioUnitStatus HandleRenderDelegate(AudioUnitRenderActionFlags actionFlags, AudioTimeStamp timeStamp, uint busNumber, uint numberFrames, AudioBuffers data)
{
    var left = (float*)data[0].Data;
    var right = (float*)data[1].Data;

    for (var i = 0; i < numberFrames; i++)
    {
        float sampleValue = (float)Math.Sin(sample * 2 * Math.PI * 440 / 44100);
        left[i] = right[i] = sampleValue;
        sample++;
    }
    return AudioUnitStatus.OK;
}

回调正在运行，缓冲区正在填充，但没有声音产生。 该示例在iOS上运行，使用AudioTypeOutput.Remote代替AudioTypeOutput.Default但由于某些原因，macOS无法播放声音。 有任何想法吗？

Answer 1

混音器的输出音量必须手动设置，因为它的默认值为0。