NAudio WasapiLoopbackCapture intermittent sound

Question

Part 1
I have some NAudio related code

    private void InitAudioOut(DateTime dtNow)
    {
        _pathOut = string.Format(BaseDirectory + @"\({0:HH-mm-ss dd-MM-yyyy} OUT).wav", dtNow);

        _waveOut = new WasapiLoopbackCapture();
        _waveOut.DataAvailable += WaveOutDataAvailable;
        _waveOut.RecordingStopped += WaveOutRecordStopped;

        _waveOutFileStream = new WaveFileWriter(_pathOut, _waveOut.WaveFormat);

        _waveOut.StartRecording();
    }

With this initialization of the sound recording process I have the followind WaveOutDataAvailable method:

    private void WaveOutDataAvailable(object sender, WaveInEventArgs e)
    {
        var buf= e.Buffer;
        _waveOutFileStream.Write(buf, 0, buf.Length);
        _waveOutFileStream.Flush();
    }

The sound in the resulting file is intermittent and slow, like having "blank" sections between the sound chunks, any ideas are appreciated.

End of part 1

Part 2
There is another version of this code where i'm trying to convert the WAV stream to mp3 stream on the fly and then write it to file, it looks like this:

    private void InitAudioIn(DateTime dtNow)
    {
        _pathIn = string.Format(BaseDirectory + @"\({0:HH-mm-ss dd-MM-yyyy} IN).mp3", dtNow);
        _waveIn = new WaveInEvent();
        _waveIn.WaveFormat = new WaveFormat(44100, 2);

        _waveIn.DataAvailable += WaveInDataAvailable;
        _waveIn.RecordingStopped += WaveInRecordStopped;

        _waveInFileStream = File.Create(_pathIn);

        _waveIn.StartRecording();
    }

With the WaveInDataAvailable method as follows:

    private void WaveInDataAvailable(object sender, WaveInEventArgs e)
    {
        var wavToMp3Buffer = ConvertWavToMp3(e.Buffer, _waveIn.WaveFormat);
        _waveInFileStream.Write(wavToMp3Buffer, 0, wavToMp3Buffer.Length);
        _waveInFileStream.Flush();
    }

The ConvertWavToMp3 method:

    public byte[] ConvertWavToMp3(byte[] wavContent, WaveFormat waveFormat)
    {
        using (var baseMemoryStream = new MemoryStream())
        using (var wavToMp3Writer = new LameMP3FileWriter(baseMemoryStream, waveFormat, 64))
        {
            wavToMp3Writer.Write(wavContent, 0, wavContent.Length);
            wavToMp3Writer.Flush();
            return baseMemoryStream.ToArray();
        }
    }

If i don't try to convert it to MP3 and just write it as a WAV file that it's absolutely fine, but if i try the MP3 conversion through the ConvertWavToMp3 method then the sound gets slow and intermittent, what is wrong with this implementation?

Answer 1

First part, you are making an invalid assumption about the buffer length being the same as the number of valid bytes in the buffer. Try:

private void WaveOutDataAvailable(object sender, WaveInEventArgs e)
{
    _waveOutFileStream.Write(e.Buffer, 0, e.BytesRecorded);
}

Let the output stream handle flushing automatically. Trying to force data to disk like that will either not work or in some cases can cause unexpected results like partial block writes that can interfere with your data. Flush at the end of the recording, not during.

As to the second part...

Your code is creating a file that is the concatenation of a series of MP3 files, one for each buffer passed to your WaveInDataAvailable method, and including all the blank space at the end of those buffers. Of course it's not going to play back properly.

If you want to write an MP3 then do it directly. Make your _waveInFileStream an instance of LameMP3FileWriter and let it handle the work itself. Not only is this going to produce a much more useful output but you save yourself a lot of inefficient messing around with setting up and tearing down the encoder for every data block you receive.