gstreamer/subprojects/gst-plugins-good/gst/cutter/filter.func

{
  guint j;
  register double squaresum = 0.0;

  /*
   * process data here  
   * input sample data enters in *in_data as 8 or 16 bit data
   * samples for left and right channel are interleaved
   */

  for (j = 0; j < num_samples; j++) 
     squaresum += data[j] * data[j];

  return (squaresum / (float) num_samples);
}