[mythtv] Mytharchive - bad subsid-track mp2 to ac3 conversion

John Pilkington J.Pilk at tesco.net
Sun Feb 10 23:23:46 UTC 2008


Paul Harrison wrote:
> John Pilkington wrote:
>> I just installed the latest ATrpms build: 0.21-175_trunk_r15741.el5.i386
>>
>> As suggested by the wiki I have Mytharchive converting the two native 
>> mp2 audio channels to ac3.  The subsidiary track is garbled in the dvd 
>> image - Donald Duck effect.   Same in mplayer and internal .iso player.
>>
>> With the earlier 15447 build I had noticed that the two audio streams 
>> before the remux were both the same size.  I now find that the 
>> subsidiary track is garbled on a DVD burned with that build.
>>
>> I don't think I really need to do the mp2 to ac3 thing - it's just a 
>> workaround to help players that can't handle both, and the title music 
>> is supplied as ac3.
>>
>> For the original recording as input after mythtranscode:
>>
>> $ ffmpeg -i 3009_20080207205900.mpg
>>
>> Input #0, mpeg, from '3009_20080207205900.mpg':
>>    Duration: 00:58:59.3, start: 0.298589, bitrate: 3569 kb/s
>>      Stream #0.0[0x1e0]: Video: mpeg2video, yuv420p, 720x576 [PAR 64:45 
>> DAR 16:9], 15000 kb/s, 25.00 tb(r)
>>      Stream #0.1[0x1c0]: Audio: mp2, 48000 Hz, stereo, 256 kb/s
>>      Stream #0.2[0x1c1]: Audio: mp2, 48000 Hz, mono, 64 kb/s
>>
>> and in the working directory:
>>
>> ffmpeg -i VTS_02_1.VOB
>>
>> Input #0, mpeg, from 'VTS_02_1.VOB':
>>    Duration: 00:38:45.1, start: 0.160000, bitrate: 3694 kb/s
>>      Stream #0.0[0x1e0]: Video: mpeg2video, yuv420p, 720x576 [PAR 64:45 
>> DAR 16:9], 15000 kb/s, 25.00 tb(r)
>>      Stream #0.1[0x80]: Audio: liba52, 48000 Hz, stereo, 192 kb/s
>>      Stream #0.2[0x81]: Audio: liba52, 48000 Hz, mono, 192 kb/s
>>
>> Thanks to Paul H for the recent native-mode patch.
>>
>> John P
>>
>>   
> 
> I've just tried to reproduce this and it worked OK for me. I had a hard
> time finding a recording where the secondary audio track was actually
> being used but did eventually find a film with an audio described track
> for the second track mono, mp2, 64kb/s just like your original. I chose
> not to re-encode the file but did chose to re-encode the audio to ac3
> which looks to be what you did and both audio tracks played fine in the
> internal player, mplayer and with xine.
> 
> If you still have the work directory intact you could look in there for
> the ac3 sound track and see if it plays OK.
> 
> Paul H.

The work directory is cleaned up in the version that I have after an 
apparently successful run, but I have a 100Kb .ac3 sample stripped out 
of the .VOB file, and that shows the effect when played in Mplayer.  My 
commercial DVD player does too, on the burned disk.

I see that the re-encoding is done by ffmpeg.  I'm using the ATrpms 
stable build > ffmpeg-0.4.9-25_r11517.el5.i386

John P




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