Question

Is there any open source C# code or library to present a graphical waveform given a byte array?

Answer 1

This is as open source as it gets:

public static void DrawNormalizedAudio(ref float[] data, PictureBox pb,
    Color color)
{
    Bitmap bmp;
    if (pb.Image == null)
    {
        bmp = new Bitmap(pb.Width, pb.Height);
    }
    else
    {
        bmp = (Bitmap)pb.Image;
    }

    int BORDER_WIDTH = 5;
    int width = bmp.Width - (2 * BORDER_WIDTH);
    int height = bmp.Height - (2 * BORDER_WIDTH);

    using (Graphics g = Graphics.FromImage(bmp))
    {
        g.Clear(Color.Black);
        Pen pen = new Pen(color);
        int size = data.Length;
        for (int iPixel = 0; iPixel < width; iPixel++)
        {
            // determine start and end points within WAV
            int start = (int)((float)iPixel * ((float)size / (float)width));
            int end = (int)((float)(iPixel + 1) * ((float)size / (float)width));
            float min = float.MaxValue;
            float max = float.MinValue;
            for (int i = start; i < end; i++)
            {
                float val = data[i];
                min = val < min ? val : min;
                max = val > max ? val : max;
            }
            int yMax = BORDER_WIDTH + height - (int)((max + 1) * .5 * height);
            int yMin = BORDER_WIDTH + height - (int)((min + 1) * .5 * height);
            g.DrawLine(pen, iPixel + BORDER_WIDTH, yMax, 
                iPixel + BORDER_WIDTH, yMin);
        }
    }
    pb.Image = bmp;
}

This function will produce something like this:

This takes an array of samples in floating-point format (where all sample values range from -1 to +1). If your original data is actually in the form of a byte[] array, you’ll have to do a little bit of work to convert it to float[]. Let me know if you need that, too.

Update: since the question technically asked for something to render a byte array, here are a couple of helper methods:

public float[] FloatArrayFromStream(System.IO.MemoryStream stream)
{
    return FloatArrayFromByteArray(stream.GetBuffer());
}

public float[] FloatArrayFromByteArray(byte[] input)
{
    float[] output = new float[input.Length / 4];
    for (int i = 0; i < output.Length; i++)
    {
        output[i] = BitConverter.ToSingle(input, i * 4);
    }
    return output;
}

Update 2: I forgot there’s a better way to do this:

public float[] FloatArrayFromByteArray(byte[] input)
{
    float[] output = new float[input.Length / 4];
    Buffer.BlockCopy(input, 0, output, 0, input.Length);
    return output;
}

I’m just so in love with for loops, I guess.