RawSourceWaveStream.md

Using RawSourceWaveStream

RawSourceWaveStream is useful when you have some raw audio, which might be PCM or compressed, but it is not contained within a file format. RawSourceWaveStream allows you to specify the WaveFormat associated with the raw audio. Let's see some examples.

Playing from a Byte array

Suppose we have a byte array containing raw 16 bit mono PCM, and want to play it.

For demo purposes, let's create a 5 second sawtooth wave into the raw. Obviously SignalGenerator would be a better way to do this, but we are simulating getting a byte array from somewhere else, maybe received over the network.

var sampleRate = 16000;
var frequency = 500;
var amplitude = 0.2;
var seconds = 5;

var raw = new byte[sampleRate * seconds * 2];

var multiple = 2.0*frequency/sampleRate;
for (int n = 0; n < sampleRate * seconds; n++)
{
    var sampleSaw = ((n*multiple)%2) - 1;
    var sampleValue = sampleSaw > 0 ? amplitude : -amplitude;
    var sample = (short)(sampleValue * Int16.MaxValue);
    var bytes = BitConverter.GetBytes(sample);
    raw[n*2] = bytes[0];
    raw[n*2 + 1] = bytes[1];
}

RawSourceWaveStream takes a Stream and a WaveFormat. The WaveFormat in this instance is 16 bit mono PCM. The stream we can use MemoryStream for, passing in our byte array.

var ms = new MemoryStream(raw);
var rs = new RawSourceWaveStream(ms, new WaveFormat(sampleRate, 16, 1));

And now we can play the RawSourceWaveStream just like it was any other WaveStream:

var wo = new WaveOutEvent();
wo.Init(rs);
wo.Play();
while (wo.PlaybackState == PlaybackState.Playing)
{
    Thread.Sleep(500);
}
wo.Dispose();

Turning a raw file into WAV

Suppose we have a raw audio file and we know the wave format of the audio in it. Let's say its 8kHz 16 bit mono. We can just open the file with File.OpenRead and pass it into a RawSourceWaveStream. Then we can convert it to a WAV file with WaveFileWriter.CreateWaveFile.

var path = "example.pcm";
var s = new RawSourceWaveStream(File.OpenRead(path), new WaveFormat(8000,1));
var outpath = "example.wav";
WaveFileWriter.CreateWaveFile(outpath, s);

Note that WAV files can contain compressed audio, so as long as you know the correct WaveFormat structure you can use that. Let's look at a compressed audio example next.

Converting G.729 audio into a PCM WAV

Suppose we have a .g729 file containing raw audio compressed with G.729. G.729 isn't actually a built-in WaveFormat in NAudio (some other common ones like mu and a-law are). But we can use WaveFormat.CreateCustomFormat or even derive from WaveFormat to define the correct format.

Now in the previous example we saw how we could create a WAV file that contains the G.729 audio still encoded. But if we wanted it to be PCM, we'd need to use WaveFormatConversionStream.CreatePcmStream to look for an ACM codec that understands the incoming WaveFormat and can turn it into PCM.

Please note that this won't always be possible. If your version of Windows doesn't have a suitable decoder, this will fail.

But here's how we would convert that raw G.729 file into a PCM WAV file if we did have a suitable decoder:

var inFile = @"c:\users\mheath\desktop\chirpg729.g729";
var outFile = @"c:\users\mheath\desktop\chirpg729.wav";
var inFileFormat = WaveFormat.CreateCustomFormat(
            WaveFormatEncoding.G729,
            8000, // sample rate
            1, // channels
            1000, // average bytes per second
            10, // block align
            1); // bits per sample
using(var inStream = File.OpenRead(inFile))
using(var reader = new RawSourceWaveStream(inStream, inFileFormat))
using(var converter = WaveFormatConversionStream.CreatePcmStream(reader))
{
    WaveFileWriter.CreateWaveFile(outFile, converter);
}

If it was a format that NAudio has built-in support for like G.711 a-law, then we'd do it like this:

var inFile = @"c:\users\mheath\desktop\alaw.bin";
var outFile = @"c:\users\mheath\desktop\alaw.wav";
var inFileFormat = WaveFormat.CreateALawFormat(8000,1);
using(var inStream = File.OpenRead(inFile))
using(var reader = new RawSourceWaveStream(inStream, inFileFormat))
using(var converter = WaveFormatConversionStream.CreatePcmStream(reader))
{
    WaveFileWriter.CreateWaveFile(outFile, converter);
}