[mythtv-users] mytharchive audio broken

Rod Smith mythtv at rodsbooks.com
Tue Sep 11 20:55:11 UTC 2007

On Tuesday 11 September 2007 15:37:32 Joe Ripley wrote:
> On 9/11/07, P Mancuso <p_mancuso at hotmail.com> wrote:
> > My Hauppauge PVR-350 saves stuff as 480x480. I can play back the
> > recordings fine. I just can't seem to get it to re-encode to DVD SP
> > format...or any other DVD format for that matter. When mytharchive
> > completes, the VIDEO_TS directory has the expected stuff in it, but the
> > AUDIO_TS directory is empty...so the resulting image won't play.
> As far as I know the AUDIO_TS directory should be empty for a video
> DVD.  It is only used for a DVD-Audio disc.

As Joe says, the AUDIO_TS directory should ordinarily be empty -- or at least, 
it always is for me. If you (P Mancuso) have actually tried playing your DVDs 
and don't hear any sound, then another problem is the issue. I recently ran 
into this myself, after upgrading from 0.20.whatever (included with Ubuntu 
6.10) to 0.20.2.whatever (for SchedulesDirect support). In my case, it turns 
out that something about the upgrade broke something about support for the 
MP2 audio tracks generated by my MPEG-2 encoding cards. Previously, I was 
able to record such files to DVD, keeping the MP2 audio tracks, and the DVDs 
would play fine on my standalone DVD player or on MythTV's MythDVD player. 
This despite the fact that MP2 is officially unsupported as a primary audio 
track on Region 1 DVDs; on such DVDs, primary audio is supposed to be in AC3 
format, or so I understand. (I figure my DVDs might not play correctly on 
some DVD players, but they played fine on MythDVD, from xine, and on my one 
standalone player, so I wasn't too concerned about this.) With the upgrade, 
my standalone player and (IIRC) xine can still play the MP2 audio tracks 
generated by the new MythArchive, but MythDVD can't. MythDVD continues to be 
able to play my old DVDs, but newly created ones cause MythDVD to output 
silence for the actual video, although the intro video and menu music plays 
correctly. I originally suspected that the cause is that the new version has 
intro tracks and menu music tracks encoded as AC3, but when I replaced these 
items with old ones that used MP2, I got the same results, so there's 
something else going on that I have yet to figure out.

In any event, the easiest workaround for me was to locate the "Always Encode 
to AC3" option in the MythArchive setup screens and activate it. This causes 
MythArchive to convert the MP2 audio track to AC3 format, and the resulting 
DVD plays fine on both MythDVD and my standalone DVD player. The main 
downside is that the conversion greatly increases the volume, sometimes to 
the point of introducing distortion. I've hacked the
/usr/share/mythtv/mytharchive/scripts/mythburn.py script to add a 
volume-adjustment option. The original line (wrapped in e-mail) was:

        cmd += "-i '%s' -f ac3 -ab 192k -ar 48000 '%s'" %(sourcefile, 

I've changed this to:

        cmd += "-i '%s' -f ac3 -vol 128 -ab 192k -ar 48000 '%s'" %(sourcefile, 

Note the addition of the "-vol 128" option. This change helps the volume 
problem. (Note that the program the script calls to do this is ffmpeg. 
Although the -vol option isn't mentioned in the man page, it is supported and 
does work. -vol 256 is theoretically "normal" volume, and appears to be the 
default.) I suspect that the optimum -vol value would vary depending on the 
volume in your source file and in all the equipment involved in audio 
playback, so if you need to adjust this feature you may need to experiment. 
The AC3 output also means I need to futz with my tuner's audio settings to 
make use of the center channel, which is a minor nuissance, but I can live 
with that. I don't know if this would be a common issue or if it's just a 
matter of how my particular tuner deals with different types of input 
streams. In theory, the fully-AC3 DVDs should conform better to the Region 1 
DVD standards, so objectively this is probably an improvement, although I 
personally prefer having MP2 audio, at least for programs originally recorded 
with that format. (Now, if there were an option to convert surround sound as 
encoded in stereo broadcasts into true 5.1-channel AC3 with active center and 
rear speakers, that'd be the best option, but I don't know of a way to do 
this. Theoretically mencoder can do it, but my experiments with that so far 
have been only partly successful.)

Rod Smith

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