[mythtv] [mythtv-commits] Ticket #2468: Mythtranscode removing, audio and subtitles and audio tracks swapping places.

[Bill Cizek]

>>
>> I transcode recordings with multiple audio streams daily, I've not 
>> seen swapping of the audio streams in a very long time.
>
> I'm seeing removal of the audio track when transcoding DVB-T 
> recordings. This happens only for some recordings. Issue has been 
> discussed in IRC and I should have 10M example file somewhere..
>
> I think I'll create a fresh ticket for this particular problem at some 
> point.

FWIW: Last night I transcoded "24" to cut commercials, and it swapped 
the audio tracks:

-Before-

Input #0, mpegts, from '/hdtv/TV/1321_20090330194800.mpg':
   Duration: 01:18:52.6, start: 29629.122578, bitrate: 12578 kb/s
     Stream #0.0[0x31]: Video: mpeg2video, yuv420p, 1280x720 [PAR 1:1 
DAR 16:9], 19000 kb/s, 59.94 tb(r)
     Stream #0.1[0x34](eng): Audio: ac3, 48000 Hz, 5:1, 448 kb/s
     Stream #0.2[0x35](spa): Audio: ac3, 48000 Hz, mono, 192 kb/s

-After-

Input #0, mpeg, from '/hdtv/TV/1321_20090330194800.mpg.tmp':
   Duration: 00:42:44.3, start: 0.335400, bitrate: 10862 kb/s
     Stream #0.0[0x1e0]: Video: mpeg2video, yuv420p, 1280x720 [PAR 1:1 
DAR 16:9], 19000 kb/s, 59.94 tb(r)
     Stream #0.1[0x81]: Audio: ac3, 48000 Hz, mono, 192 kb/s
     Stream #0.2[0x80]: Audio: ac3, 48000 Hz, 5:1, 448 kb/s

------------

But... I run 0.21-fixes, so it could be something that's fixed in trunk 
and not backported.

As for removing audio tracks, a long time ago I ran into this (see 
ticket #1841). In my case, the transcoder gave up looking for the audio 
track before it was found. I've used the following patch for the last 
few years to avoid this problem. It increases the max # frames to read 
from 45 to 1000, and logs the actual number of frames read before it 
found the audio tracks.


Index: mythtv/libs/libavformat/utils.c
===================================================================
--- mythtv/libs/libavformat/utils.c     (revision 11597)
+++ mythtv/libs/libavformat/utils.c     (working copy)
@@ -1989,7 +1989,7 @@
 #define MAX_READ_SIZE        5000000
 
 /** Number of frames to read, max. */
-#define MAX_FRAMES           45
+#define MAX_FRAMES           1000
 
 /** Maximum duration until we stop analysing the stream. */
 #define MAX_STREAM_DURATION  ((int)(AV_TIME_BASE * 3.0))
@@ -1958,12 +1958,16 @@
                 (read_size >= MAX_READ_SIZE || read_packets >= 
MAX_FRAMES) ||
                 (hasvideo && hasaudio)) {
                 /* if we found the info for all the codecs, we can stop */
+                av_log(ic, AV_LOG_INFO, "Stopping1 after %d bytes, %d 
frames, hasvideo = %d, hasaudio = %d\n",
+                           read_size, read_packets, hasvideo, hasaudio);
                 ret = count;
                 break;
             }
         }
         /* we did not get all the codec info, but we read too much data */
         if (read_size >= MAX_READ_SIZE) {
+            av_log(ic, AV_LOG_INFO, "Stopping2 after %d bytes, %d 
frames, hasvideo = %d, hasaudio = %d\n",
+                       read_size, read_packets, hasvideo, hasaudio);
             ret = count;
             break;
         }