Поработав с этой библиотекой и собрав несколько разных рекомендаций из разных источников, я получил кое-что, что наконец-то сработало, так что, надеюсь, это избавит других от головной боли.
Iпо сути, мне приходилось накатывать свой собственный IWaveProvider и выполнять различные пользовательские фильтры и еще много чего, пока он не заработал.
public class MuLawResamplerProvider : IWaveProvider
{
public WaveFormat WaveFormat => WaveFormat.CreateMuLawFormat(8000, 1);
private BufferedWaveProvider waveBuffer;
private IWaveProvider ieeeToPcm;
private byte[] sourceBuffer;
/// <summary>
/// Converts from 32-bit Ieee Floating-point format to MuLaw 8khz 8-bit 1 channel.
/// Used for WasapiCapture and WasapiLoopbackCapture.
/// </summary>
/// <param name="audio">The raw audio stream.</param>
/// <param name="inputFormat">The input format.</param>
public MuLawResamplerProvider(byte[] stream, WaveFormat inputFormat)
{
// Root buffer provider.
waveBuffer = new BufferedWaveProvider(inputFormat);
waveBuffer.DiscardOnBufferOverflow = false;
waveBuffer.ReadFully = false;
waveBuffer.AddSamples(stream, 0, stream.Length);
var sampleStream = new WaveToSampleProvider(waveBuffer);
// Stereo to mono filter.
var monoStream = new StereoToMonoSampleProvider(sampleStream)
{
LeftVolume = 2.0f,
RightVolume = 2.0f
};
// Downsample to 8000 filter.
var resamplingProvider = new WdlResamplingSampleProvider(monoStream, 8000);
// Convert to 16-bit in order to use ACM or MuLaw tools.
ieeeToPcm = new SampleToWaveProvider16(resamplingProvider);
sourceBuffer = new byte[ieeeToPcm.WaveFormat.AverageBytesPerSecond];
}
/// <summary>
/// Reset the buffer to the starting position with a new stream.
/// </summary>
/// <param name="stream">New stream to initialize.</param>
public void Reset(byte[] stream)
{
waveBuffer.ClearBuffer();
waveBuffer.AddSamples(stream, 0, stream.Length);
}
/// <summary>
/// Converts the 16-bit ACM stream to 8-bit MuLaw on read.
/// </summary>
/// <param name="destinationBuffer">The destination buffer to output into.</param>
/// <param name="offset">The offset to store at.</param>
/// <param name="readingCount">The requested size to read.</param>
/// <returns></returns>
public int Read(byte[] destinationBuffer, int offset, int readingCount)
{
// Source buffer has twice as many items as the output array.
var sizeOfPcmBuffer = readingCount * 2;
sourceBuffer = BufferHelpers.Ensure(sourceBuffer, sizeOfPcmBuffer);
var sourceBytesRead = ieeeToPcm.Read(sourceBuffer, 0, sizeOfPcmBuffer);
var samplesRead = sourceBytesRead / 2;
var outIndex = 0;
for (var n = 0; n < sizeOfPcmBuffer; n += 2)
{
destinationBuffer[outIndex++] = MuLawEncoder.LinearToMuLawSample(BitConverter.ToInt16(sourceBuffer, offset + n));
}
return samplesRead;
}
}
И тогда вы можете сделать что-то столь же простое, как это
var resampler = new MuLawResamplerProvider(deviceStream.ToArray(), ActiveWasapiCaptureDevice.WaveFormat);
// Write it out to a local file
string path = @"C:\Temp\" + Guid.NewGuid().ToString() + ".wav";
WaveFileWriter.CreateWaveFile(path, resampler);
resampler.Reset(deviceStream.ToArray());
// Write it into memory for other uses
MemoryStream outputStream = new MemoryStream();
WaveFileWriter.WriteWavFileToStream(outputStream, resampler);