[mythtv-users] Transcoding: Audio/Video Sync

David Smith djs98052 at gmail.com
Tue Dec 7 18:50:29 UTC 2004

Hi Matt,

I'm not familiar with the command line parameters to mythtranscode,
but are you using the cutlist, or removing commercials as part of the

This is just a theory, but I'm wondering if a cut point occurs between
keyframes in the MPEG stream if this loss of synchronization will
occur.  Perhaps the video is processed all the way to the cutpoint,
but the audio processing stops at the keyframe, or vice-versa.  Maybe
others can confirm or deny this theory.

I had a similar problem with NUVEXPORT, but only on one recording. 
I've done several others and haven't seen the same issue and I didn't
cut them on the keyframe intentionally.


P.S. That's one of my favorite James Bond films!

On Tue, 07 Dec 2004 12:36:43 -0500, Matt Vollmar <matt at vollmars.com> wrote:
> OK, I know this has been hashed around a bunch on this list, and I
> searched for anything that might help, but I couldn't find something to
> address this issue (I'm sure I didn't search long enough).  I transcoded
> (manually from the command line) a movie last night, and looked at it
> today to find an ever so slow loss of sync between audio and video.  The
> video ends up about .5 seconds faster by the end of the movie.  In the
> original, it is not thus.  Is there a way for me to fix this?  Here is
> the command line stuff I use:
> mythtranscode --showprogress -p autodetect -c 1073 -s
> 2004-11-25-12-00-00 -f . 2>&1 > /dev/null
> ffmpeg -f rawvideo -s 480x480 -r 29.97 -i ./vidout -y -f s16le -ar 32000
> -ac 2 -i ./audout -b 1152 -vcodec mpeg1video -s 640x480 -hq -deinterlace
> -qmax 3 -qmin 13 -ar 44100 -aspect 4:3 "./You_Only_Live_Twice.mpg"
> It is possible that some of my parameters are not correct.  I got these
> from someone who said they were good quality, which they are very
> acceptable.  Plus, it transcodes at just a hair slower than real-time,
> so that part rules.  Should I use fifosync on the mythtranscode command
> line or what?  Should I not deinterlace?
> Thanks for any help,
> Matt
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