How to render audio waveform?

Question

1. Is there any audio/programming-related stack-exchange site?
2. I'm trying to make a wave form in WinForms
3. What algorithm should I use?

For example, if I have 200 samples per pixel (vertical line), should I draw the lowest and the highest sample from that portion of 200 samples? Or should I draw average of low and high samples? Maybe both in different colors?

Answer 1

This will help you to generate waveform from audio file using nAudio in C#...

using NAudio.Wave;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class test : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    string strPath = Server.MapPath("audio/060.mp3");
    string SongID = "2";
    byte[] bytes = File.ReadAllBytes(strPath);
    WriteToFile(SongID,strPath, bytes);
    Response.Redirect("Main.aspx");
    }

private void WriteToFile(string SongID, string strPath, byte[] Buffer)
{
    try
    {
        int samplesPerPixel = 128;
        long startPosition = 0;
        //FileStream newFile = new FileStream(GeneralUtils.Get_SongFilePath() + "/" + strPath, FileMode.Create);
        float[] data = FloatArrayFromByteArray(Buffer);

        Bitmap bmp = new Bitmap(1170, 200);

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

        NAudio.Wave.Mp3FileReader reader = new NAudio.Wave.Mp3FileReader(strPath, wf => new NAudio.FileFormats.Mp3.DmoMp3FrameDecompressor(wf));
        NAudio.Wave.WaveChannel32 channelStream = new NAudio.Wave.WaveChannel32(reader);

        int bytesPerSample = (reader.WaveFormat.BitsPerSample / 8) * channelStream.WaveFormat.Channels;

        using (Graphics g = Graphics.FromImage(bmp))
        {

            g.Clear(Color.White);
            Pen pen1 = new Pen(Color.Gray);
            int size = data.Length;

            string hexValue1 = "#009adf";
            Color colour1 = System.Drawing.ColorTranslator.FromHtml(hexValue1);
            pen1.Color = colour1;

            Stream wavestream = new NAudio.Wave.Mp3FileReader(strPath, wf => new NAudio.FileFormats.Mp3.DmoMp3FrameDecompressor(wf));

            wavestream.Position = 0;
            int bytesRead1;
            byte[] waveData1 = new byte[samplesPerPixel * bytesPerSample];
            wavestream.Position = startPosition + (width * bytesPerSample * samplesPerPixel);

            for (float x = 0; x < width; x++)
            {
                short low = 0;
                short high = 0;
                bytesRead1 = wavestream.Read(waveData1, 0, samplesPerPixel * bytesPerSample);
                if (bytesRead1 == 0)
                    break;
                for (int n = 0; n < bytesRead1; n += 2)
                {
                    short sample = BitConverter.ToInt16(waveData1, n);
                    if (sample < low) low = sample;
                    if (sample > high) high = sample;
                }
                float lowPercent = ((((float)low) - short.MinValue) / ushort.MaxValue);
                float highPercent = ((((float)high) - short.MinValue) / ushort.MaxValue);
                float lowValue = height * lowPercent;
                float highValue = height * highPercent;
                g.DrawLine(pen1, x, lowValue, x, highValue);

            }
        }

        string filename = Server.MapPath("image/060.png");
        bmp.Save(filename);
        bmp.Dispose();

    }
catch (Exception e)
    {

    }
}
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;
}

}