[mythtv-commits] Ticket #11639: Audio lost after transcode

[MythTV]

#11639: Audio lost after transcode
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 Reporter:  oli.henning@…    |           Type:  Bug Report - General
   Status:  new              |       Priority:  major
Milestone:  unknown          |      Component:  MythTV - Mythtranscode
  Version:  0.26-fixes       |       Severity:  medium
 Keywords:  transcode audio  |  Ticket locked:  0
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 Since a few weeks i have a problem with mythtranscode:
 Audio is completly lost after transcoding.
 Perhaps this is the same or similar to
 http://code.mythtv.org/trac/ticket/7118

 == Details ==
 - Recording with DVB-C
 - Problem occurs just on one specific channel: "ORF 1"  (prime channel of
 austria).
 - Recorded in switzerland, cable-provider "UPC Cablecom"
 - Problem does not occur on every recording - so the problem is not
 "stable"
 - Just using "lossless MPEG-2" transcoding to cut-off commerials.
 - No audio- and no video-recompression (so it's quite fast)
 - Before the transcoding all audio-channels are present in mythfrontend
 - Changes in audio-streams-combinations within recoding is recognized in
 mythfrontend (e.g. not from the beginning but from somewhere in the middle
 of the recoding there is an AC3-stream)

 == Example-File to reproduce ==
 https://dl.dropboxusercontent.com/u/517875/2109_20130701213000.mpg
 I cutted of the first 310'200'000 Bytes. This are exactly 1'650'000 TS-
 Packets (each 188 Bytes). So this is just the first ~9 minutes of the
 original recording.
 '''Interesting fact''': If the file would be just the first 1'600'000 TS-
 Packets, then
 {{{mythtranscode}}} will __not__ have the audio-loss-problem. This is the
 reason why the test-file-to-reproduce has to be so big.

 == LOG-Output of mythtranscode ==
 {{{
 (my_av_print) Input #0, mpegts, from
 '/mnt/mythtvRecordings/2109_20130701213000.mpg':
 (my_av_print)   Duration: N/A, bitrate: N/A
 (my_av_print)     Stream #0:0[0x90]: Video: mpeg2video, 90k tbn
 (my_av_print)     Stream #0:1[0x91](ger): Audio: mp3, 0 channels
 (my_av_print)     Stream #0:2[0x9b](ger): Audio: ac3, 0 channels
 (my_av_print)     Stream #0:3[0xae](ger): Subtitle: dvb_teletext
 (InitAV) Skipping invalid audio stream: 1
 (InitAV) Skipping invalid audio stream: 2
 }}}
 You can see, that mythtranscode has some problems in identifying the
 stream-content:
 - mythtranscode could not detect the recording-duration (just logs "N/A")
 - mythtranscode could not detect details of the video-stream (pixel-
 format, frame-size, frame-rate, ...)
 - mythtranscode detected the first audio-stream as beeing "mp3". But
 actually it's a normal "mp2" audio-stream (analyzed with avprobe)

 To compare: the log of a 'normal' transcoding:
 {{{
 (my_av_print) Input #0, mpegts, from
 '/mnt/mythtvRecordings/2102_20130629193300.mpg':
 (my_av_print)   Duration: 00:44:56.88, start: 13209.723733, bitrate: 7099
 kb/s
 (my_av_print)     Stream #0:0[0x50]: Video: mpeg2video (Main), yuv420p,
 720x576 [SAR 64:45 DAR 16:9], 15000 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
 (my_av_print)     Stream #0:1[0x51](deu): Audio: mp2, 48000 Hz, stereo,
 s16, 192 kb/s
 (my_av_print)     Stream #0:2[0x52](eng): Audio: mp2, 48000 Hz, stereo,
 s16, 192 kb/s
 (my_av_print)     Stream #0:3[0x6e](deu): Data: dvb_vbi
 (InitAV) Skipping unsupported codec 2 on stream 3
 }}}

 On request i can do further investigations. Perhaps you have to name me
 some analyze-tools.

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Ticket URL: <http://code.mythtv.org/trac/ticket/11639>
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