[mythtv-users] Audio sync problems with exported Myth recordings - not with manual recordings

Lane Schwartz dowobeha at gmail.com
Tue Dec 14 02:39:17 UTC 2004

On Mon, 13 Dec 2004 14:40:31 -0800, Scott Alfter
<mythtv at salfter.dyndns.org> wrote:
> On Mon, Dec 13, 2004 at 03:22:19PM -0600, Lane Schwartz wrote:
> > I've hit a big snag - when I export the recordings and cut the
> > commercials with nuvexport (MPEG2->MPEG2), the audio on the exported
> > recording is way out of sync. Note that when I play the original files
> > in Myth or mplayer, the audio sync is just fine.
> >
> > I tried opening the recording with avidemux, cutting the commercials,
> > exporting raw audio and video, then manually remuxing them with mplex
> > (as per instructions in section 21.19 of Mythtv.org docs). I still get
> > a final mpg with out-of-sync audio.
> Since the files play back properly, that would rule out MythTV and ivtv as
> the source of the problem.  nuvexport appears to not work at all for me...it
> grinds away for several minutes but ends up producing nothing.

I thought about that. But I also think that the problem could still be
ivtv or Myth. After all, the files play just fine - but there could be
something screwed up in the MPEG encoding that makes them unfit for
editing. I have no way to prove that, but I'm wondering...

> I have copied several MPEG-2 program streams over to a Windows box and
> edited them with a combination of DVD2AVI, Avisynth, LAME, BeSweet, and
> TMPGEnc.  The DVDs that I've made from shows processed this way have all
> worked flawlessly, with no sync problems.  That would also rule out MythTV
> and ivtv as the source of your problem; it sounds more like an issue with
> nuvexport and/or the apps nuvexport calls on to do its work.
> (What those issues would be, though, I don't know.  I haven't had much time
> to play with nuvexport yet, and I suspect that if I want to put Enterprise
> on DVD at 4400 kbps video, I'd probably get better quality by recording at a
> higher (6000-8000 kbps) rate, editing, and reencoding with TMPGEnc at 4400
> kbps VBR than by recording at 4400 kbps (the PVRx50's encoder is CBR,
> right?) and dumping that to DVD.  I've not tried a comparison of the two,
> but my gut instinct is that at a given target bitrate, a non-real-time
> software encoder can produce better results than a real-time hardware
> encoder.)

You may be right, but software encoding wastes so much time that I
don't really consider it to be an option. That's the whole reason I
have a PVR-250. Plus, the really annoying thing is that I had it all
working on my old box running FC1. If I have time over Christmas I may
try to revert to a 2.4 kernel with a corresponding older ivtv.

Does anyone with a PVR-250 have exporting to DVD working successfully
using MPEG2->MPEG2 cutting?


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