[mythtv-users] DVD recording sync issues with PVR 350

Cory Papenfuss papenfuss at juneau.me.vt.edu
Thu May 5 12:13:34 UTC 2005


> I am writing some of my MythTV recordings to DVD and I
> get a-v sync drifts during the DVD recording, up to a
> second or two near the end of a two-hour recording
> (playing within myth is fine, though).  I've noticed
> that many people have this problem, but all the
> solutions I've tried that people suggested haven't
> worked for me.  For reference, I'm using a PVR-350,
> Myth 0.18, ivtv-0.2.0-rc3e, on a headless system
> running on a Celeron 566 with SuSE Linux 9.2.
>
 	Most likely due to changing A/V sync within the MPEG2 stream. 
It's a known problem without a known (bug-free) solution.

> To burn to DVD, I have a script crafted after the
> mythtv docs ala the blurb at the end of
> http://mythtv.org/docs/mythtv-HOWTO-22.html.  This
> involves splitting the audio and video streams with
> mpeg2desc, remultiplexing them with mplex, creating a
> dvd file structure with dvdauthor, and writing an iso
> file system directly to DVD with growisofs.
>
 	The demuxing/remuxing is the root of the evil here.  All 
*relative* sync information is lost in this process.  It's fine if the 
sync doesn't change throughout the stream, but ivtv captures will 
sometimes glitch the sync.

> Basically, I've tried:
>
> 1) Changing the encoded stream type to "DVD Special 2"
> in Myth.  Still have the sync issue.
 	I think those "encoded stream types" in the ivtv are for the most 
part like the darkness knob on a toaster.  It just makes you *think* 
you're in control.

  > 2) Trying to re-encode using mencoder like the
> following:
>
>> mencoder <nuv file> -of mpeg -oac copy -ovc copy -o
> <new nuv file>
>
 	That's not reencoding... just copying the stream and remuxing it 
on-the-fly.

> mencoder seems to do just fine, but when I do this,
> mpeg2desc or mplex complain that they don't understand
> the file format.
> 3) Trying to re-encode using ffmpeg, setting the
> output format to mpeg2video, making sure that audio
> bitrate is the same (384kpbs), and preserving the
> stream mappings.  The command looks something like
>
>> ffmpeg -i <nuv file> -f mpegts -vcodec mpegvideo -ab
> 384 -b 4500 -maxrate 6000 -bufsize 200 <new nuv file>
>
> Again, does just fine, but mpeg2desc or mplex complain
> that they don't like the resulting file format.
>
> ...and a few other things, including using mpgtx to
> cut the file into segments or nuvexport (I get myriad
> complaints about formats or obscure errors).
> Regarding the file format complaints, I've looked for
> settings to try that won't make mplex or mpeg2desc
> barf, but I can't find any.  The errors look like
> this:
>
>   INFO: [mplex] mplex version 1.6.2 (2.2.3 $Date:
> 2004/01/13 20:45:26 $)
> **ERROR: [mplex] File  unrecogniseable!
> **ERROR: [mplex] File  unrecogniseable!
> **ERROR: [mplex] Unrecogniseable file(s)... exiting.
>

> In any case, it seems the initial problem comes from
> errors that are generated by the PVR350's encoder.
> So, it seems the right approach would be some tool
> that can re-encode the streams while preserving the
> stream format (and the sync!) and cleaning up the
> stream errors generated by the PVR.  Keeping it
> playable on the PVR-350's output would be ideal, then
> I can try some user job in myth to do this to all the
> recordings automatically.  (In fact, maybe take a
> couple Mbps out of the file in the process.)
>
 	Yeah, wouldn't that be great?  So far, I haven't found it.

> Is there a simple, idiot-proof way to do this?  Since
> I'm running my myth system headless, something easily
> scriptable, and non-GUI is what I'm after.  I really
> hope somebody who has solved this problem can show me
> the way.
>
> Thanks!
>
 	There are about 10 different major tools that I know of that can 
be used to manipulate MPEG2 streams.  Some deal with some errors, some 
deal with others, but I haven't found any that do what's truly necessary.

-Cory

*************************************************************************
* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
*************************************************************************



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