[mythtv] [mythtv-commits] Ticket #7698: A/V Sync Broken with HD-PVR and Dish Network

Jim Stichnoth stichnot at gmail.com
Thu Dec 3 21:33:05 UTC 2009

On Thu, Dec 3, 2009 at 12:54 PM, MythTV <mythtv at cvs.mythtv.org> wrote:
> #7698: A/V Sync Broken with HD-PVR and Dish Network
> --------------------------------+-------------------------------------------
>  Reporter:  bhuffman@…          |       Owner:  danielk
>     Type:  defect              |      Status:  new
>  Priority:  minor               |   Milestone:  unknown
> Component:  MythTV - Recording  |     Version:  unknown
>  Severity:  medium              |     Mlocked:  0
> --------------------------------+-------------------------------------------
>  It appears that somewhere around the 17th of November, a problem cropped
>  up with Dish Network and the HD-PVR recorder so that the video is just a
>  little faster than the audio.  So, by 10-15 minutes into every recording
>  it's completely unbearable to watch (lips move obviously before the voice,
>  etc. etc.).  I notice that Hauppauge has released an update, but it says
>  "Windows driver only" and I've already tried connecting a windows laptop
>  to my HD-PVR and applying the update and it doesn't seem to have any
>  effect on mythtv.
>  I'm attaching a 400kB snippit of a file that exhibits this behavior.  It's
>  starting from the beginning, so it won't be as obvious, but perhaps it can
>  help.
> --
> Ticket URL: <http://svn.mythtv.org/trac/ticket/7698>

"Me too", see http://www.gossamer-threads.com/lists/mythtv/users/409441
.  Run "mplayer -vo null -ao null -frames 10 -identify filename.mpg |
grep FPS" and you'll see that a problematic recording reports 60.0 or
30.0 fps whereas an old good recording reports 59.94 or 29.97 fps.
The audio is apparently being muxed in at 59.94 or 29.97 fps, hence
the drift (video is faster than audio).  Here are some suggestions to
try (I haven't been able to properly test all of them due to some
unrelated problems):

1. Downgrade to HD-PVR firmware version

2. Set the Dish STB to output PCM only, rather than AC3 only.  The PVR
will mux in AC3 audio unmodified, but it will reencode PCM input.
Maybe the audio will get timestamps that are consistent with the

3. See if you can locate a tool that would remux the file with correct
timestamps (slowing down the video by 0.1%).  Not a great long-term
solution, but at least existing recordings could be repaired.

This is almost certainly *not* a Myth problem.  Most likely it's a
firmware problem; less likely it's an hdpvr driver problem.  I'm
curious if non-Myth DVR software is also seeing this.


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