NAudio Wasapi 录音和转换

Question

我正在使用 NAudio 并尝试使用 WasapiLoopbackCapture 记录我的电脑上正在播放的内容。我遇到的问题是我需要记录的数据为 PCM 16bit 44100khz Mono。 为此，我构建了这个：

using System;
using System.Diagnostics;

using NAudio.Wave;
using NAudio.CoreAudioApi;

namespace soundtest
{
    class Program {

        static void Main(string[] args) {
            try {
                var deviceToRecord = (new MMDeviceEnumerator().EnumerateAudioEndPoints(DataFlow.All, DeviceState.Active))[0];

                var recorder = new CustomWasapiLoopbackCapture(deviceToRecord, false, 1000 / 5);
                recorder.ShareMode = AudioClientShareMode.Shared;
                recorder.DataAvailable += recorderDataAvailable;

                var inprov = new WaveInProvider(recorder);
                var fto16prov = new WaveFloatTo16Provider(inprov);
                var stomprov = new StereoToMonoProvider16(fto16prov);

                Console.WriteLine("Press something to stop recording.");
                recorder.StartRecording();
                Console.ReadKey();
                recorder.StopRecording();

            } catch (Exception e) {
                Console.WriteLine("!!! EXCEPTION !!!" + 
                    "\nMessage:\n   " + e.Message + 
                    "\nSource:\n   " + e.Source + 
                    "\nStack:\n" + e.StackTrace);
            }

            Console.WriteLine("Press something to close.");
            Console.ReadKey();
        }

        static void recorderDataAvailable(object sender, WaveInEventArgs args) {
            // how do I access PCM 16bit here?
            // It's not args.Buffer, or am I wrong?
            // additional calculation is done here with the PCM data
        }
    }


    class CustomWasapiLoopbackCapture : WasapiCapture
    {
        public CustomWasapiLoopbackCapture() 
            : this(GetDefaultLoopbackCaptureDevice()){ }
        public CustomWasapiLoopbackCapture(MMDevice captureDevice)
            : this(captureDevice, false){ }
        public CustomWasapiLoopbackCapture(MMDevice captureDevice, bool useEventSync)
            : this(captureDevice, useEventSync, 100){ }
        public CustomWasapiLoopbackCapture(MMDevice captureDevice, bool useEventSync, int audioBufferMillisecondsLength)
            : base(captureDevice, useEventSync, audioBufferMillisecondsLength){ }

        public static MMDevice GetDefaultLoopbackCaptureDevice() {
            MMDeviceEnumerator devices = new MMDeviceEnumerator();
            return devices.GetDefaultAudioEndpoint(DataFlow.Render, Role.Multimedia);
        }

        public override WaveFormat WaveFormat
        {
            get { return base.WaveFormat; }
            set { throw new InvalidOperationException("WaveFormat cannot be set for WASAPI Loopback Capture"); }
        }

        protected override AudioClientStreamFlags GetAudioClientStreamFlags() {
            return AudioClientStreamFlags.Loopback;
        }
    }
}

如何访问转换后的录音？我认为通过添加这些提供程序，我可以获得数据以进行进一步计算。我认为 args.Buffer 没有提供预期的 PCM 16 位 44100 kHz 单声道数据的假设来自我在 recorderDataAvailable 方法中进行的额外处理的不切实际结果。我在混音板的另一个输入上使用简单的 WaveInEvent 对此进行了测试，我用它循环播放的声音。

Answer 1

WASAPI 始终将音频记录为 IEEE 浮点样本。因此，在回调中记录的缓冲区中，每 4 个字节是一个float。访问单个样本的一种简单方法是使用BitConverter.ToSingle。这将为您提供 +/- 1.0 范围内的值。所以乘以 32767，然后转换为 Int16 以将其转换为 16 位样本值。