[mythtv-users] Transcoding: Audio/Video Sync
matt at vollmars.com
Tue Dec 7 20:57:01 UTC 2004
David Smith wrote:
>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,
I did indeed use cut points, but I actually transcoded them first to cut
out the commercials, so when I am comparing these 2 videos it is really
apples to apples. I am sure that I cut them outside of the keyframes,
because I move my cut-points to the exact blank spot. I didn't realize
that this could be a problem. I will be more careful next time, but I
would still like to fix this.
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