[mythtv-users] Audio static-y in SVN

[Curtis Stanford]

On 23-Jan-08, at 9:50 PM, Curtis Stanford wrote:

> The last few versions of SVN have made the audio on Live TV and  
> recordings full of static. Sounds just like listening through broken  
> speakers. Recordings made before the update are also bad so I assume  
> the firewire recording process is OK. Also, playing the same files  
> in mplayer is OK. HD channels aren't as bad a regular for some reason.
>
> Curtis Stanford
> curtis at stanfordcomputing.com
>

To answer my own question, the culprit is the change to libs/ 
libavcodec/ac3dec.c in SVN version 15526:

Index: ac3dec.c
===================================================================
--- ac3dec.c	(revision 15577)
+++ ac3dec.c	(working copy)
@@ -1159,12 +1159,7 @@
          }
          for (i = 0; i < 256; i++)
              for (ch = 0; ch < ctx->out_channels; ch++)
-                /* HACK: triple the sample values to raise the volume
-                 * levels closer to normal when ffmpeg is used to  
decode
-                 * 5.1 or two channel AC3 to stereo out. This is  
intended
-                 * to be temporary until a proper fix is found.
-                 */
-                *(out_samples++) = ctx->int_output[ch][i] * 3;
+                *(out_samples++) = ctx->int_output[ch][i];
      }
      *data_size = NB_BLOCKS * 256 * avctx->channels * sizeof (int16_t);
      return ctx->frame_size;

This patch changes it back to pre-15526. The change screwed up my  
audio pretty bad, making it clip a lot on certain AC3 sources.

Curtis