Saturday, 26 September 2009

Trimming a WAV file using NAudio

I’m hoping to write a few brief code snippets to demonstrate various uses of NAudio, to eventually form the basis of an FAQ. This example shows how you can take a WAV file and trim a section out of it. You specify the TimeSpan to remove from the beginning and end, as well as an output WAV file. Please note this will only be reliable with PCM format WAV files.

public static class WavFileUtils
{
    public static void TrimWavFile(string inPath, string outPath, TimeSpan cutFromStart, TimeSpan cutFromEnd)
    {
        using (WaveFileReader reader = new WaveFileReader(inPath))
        {
            using (WaveFileWriter writer = new WaveFileWriter(outPath, reader.WaveFormat))
            {
                int bytesPerMillisecond = reader.WaveFormat.AverageBytesPerSecond / 1000;

                int startPos = (int)cutFromStart.TotalMilliseconds * bytesPerMillisecond;
                startPos = startPos - startPos % reader.WaveFormat.BlockAlign;

                int endBytes = (int)cutFromEnd.TotalMilliseconds * bytesPerMillisecond;
                endBytes = endBytes - endBytes % reader.WaveFormat.BlockAlign;
                int endPos = (int)reader.Length - endBytes; 

                TrimWavFile(reader, writer, startPos, endPos);
            }
        }
    }

    private static void TrimWavFile(WaveFileReader reader, WaveFileWriter writer, int startPos, int endPos)
    {
        reader.Position = startPos;
        byte[] buffer = new byte[1024];
        while (reader.Position < endPos)
        {
            int bytesRequired = (int)(endPos - reader.Position);
            if (bytesRequired > 0)
            {
                int bytesToRead = Math.Min(bytesRequired, buffer.Length);
                int bytesRead = reader.Read(buffer, 0, bytesToRead);
                if (bytesRead > 0)
                {
                    writer.WriteData(buffer, 0, bytesRead);
                }
            }
        }
    }
}
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