Unable to get wave form image for audio using NAudio

Question

Unable to get wave form image for smaller duration audio stream using this code. I am getting totally blank image. Is there any way to get correct wave form image for smaller duration audio stream. I am using NAudio's AudioFileReader function here.

        Bitmap bim = new Bitmap(1800,200);
        System.Drawing.Graphics g = Graphics.FromImage(bim);

        using (var reader = new AudioFileReader("D:\\Test-Songs\\DawnJay.mp3"))
        {
            var samples = reader.Length / (reader.WaveFormat.Channels * reader.WaveFormat.BitsPerSample / 8);
            var f = 0.0f;
            var max = 0.0f;

            // waveform will be a maximum of 4000 pixels wide:
            var batch = (int)Math.Max(40, samples / 4000);
            var mid = 100;
            var yScale = 100;
            float[] buffer = new float[batch];
            int read;
            var xPos = 0;

            Pen pen = new Pen(Color.Red, 2.0f);
            g.Clear(Color.Black);

            while ((read = reader.Read(buffer, 0, batch)) == batch)
            {
                for (int n = 0; n < read; n++)
                {
                    max = Math.Max(Math.Abs(buffer[n]), max);
                }                                      

                int X1 = xPos;
                int X2 = xPos;
                float Y1 = mid + (max * yScale);
                float Y2 = mid - (max * yScale);

                g.DrawLine(pen,X1, Y1, X2, Y2);

                max = 0;
                xPos++;
            }

        }

        bim.Save("D:\\Images\\waveform.png");

Answer 1

Your code here:

var batch = (int)Math.Max(40, samples / 4000);

This says that you are going to accept a minimum of 40 samples per column. For a small file this might mean that your data gets reduced to only a small number of columns of data in the output bitmap. If you are then scaling that data down to fit into a display area on screen, your audio data might disappear.

Try changing your minimum number of samples per block to a smaller value, which should give you a chance at actually visualizing small audio files. You should probably do full Min-Max calculations, or else your plots for very small files will look totally wrong.