Improve audio waveform quality.

This averages over the pcm samples in each image column by adding a
shade of gray. It also draws a solid white base line for each channel.

diff --git a/src/framework/mlt_frame.c b/src/framework/mlt_frame.c
index 6630af5c4e97e7c250f0d10d6af3f3c489e74604..b0afaf0ebfbe60b79bcc83f5ab5c987aa3876c6b 100644 (file)
--- a/src/framework/mlt_frame.c
+++ b/src/framework/mlt_frame.c
@@ -710,32 +710,33 @@ unsigned char *mlt_frame_get_waveform( mlt_frame this, int w, int h )
 
        // Render vertical lines
        int16_t *ubound = pcm + samples * channels;
-       int skip = samples / w - 1;
+       int skip = samples / w;
+       unsigned char gray = 0xFF / skip;
        int i, j, k;
 
        // Iterate sample stream and along x coordinate
-       for ( i = 0; i < w && pcm < ubound; i++ )
+       for ( i = 0; pcm < ubound; i++ )
        {
                // pcm data has channels interleaved
-               for ( j = 0; j < channels; j++ )
+               for ( j = 0; j < channels; j++, pcm++ )
                {
                        // Determine sample's magnitude from 2s complement;
                        int pcm_magnitude = *pcm < 0 ? ~(*pcm) + 1 : *pcm;
                        // The height of a line is the ratio of the magnitude multiplied by
                        // the vertical resolution of a single channel
-                       int height = h * pcm_magnitude / channels / 2 / 32768;
+                               int height = h * pcm_magnitude / channels / 2 / 32768;
                        // Determine the starting y coordinate - left top, right bottom
                        int displacement = h * (j * 2 + 1) / channels / 2 - ( *pcm < 0 ? 0 : height );
                        // Position buffer pointer using y coordinate, stride, and x coordinate
-                       unsigned char *p = bitmap + i + displacement * w;
+                       unsigned char *p = bitmap + i / skip + displacement * w;
 
                        // Draw vertical line
-                       for ( k = 0; k < height; k++ )
-                               p[ w * k ] = 0xFF;
-
-                       pcm++;
+                       for ( k = 0; k < height + 1; k++ )
+                               if ( *pcm < 0 )
+                                       p[ w * k ] = ( k == 0 ) ? 0xFF : p[ w * k ] + gray;
+                               else
+                                       p[ w * k ] = ( k == height ) ? 0xFF : p[ w * k ] + gray;
                }
-               pcm += skip * channels;
        }
 
        return bitmap;