[mythtv-users] lossless cut and audio sync drift?

Ian Evans dheianevans at gmail.com
Mon Dec 17 09:13:12 UTC 2012


On Fri, Nov 23, 2012 at 10:29 AM, Ian Evans <dheianevans at gmail.com> wrote:
> On Fri, Nov 23, 2012 at 7:37 AM, Doug Vaughan <r.d.vaughan at rogers.com> wrote:
>> Ian,
>>     I have, but rarely, noticed some audio drift. I am fairly sure, as so
>> many of the other issues are, that mkvmerge finds some problem with the
>> original recorded mpg file. Here is a reference to mkvmerge parameters that
>> you can use from the commandline on an out of sync mkv file post lossless
>> cut.
>>
>> From: https://www.bunkus.org/videotools/mkvtoolnix/doc/mkvmerge.html
>>
>> Some movies start synced correctly but slowly drift out of sync. For these
>> kind of movies you can specify a delay factor that is applied to all
>> timestamps -- no data is added or removed. So if you make that factor too
>> big or too small you'll get bad results. An example is that an episode I
>> transcoded was 0.2 seconds out of sync at the end of the movie which was
>> 77340 frames long. At 29.97fps 0.2 seconds correspond to approx. 6 frames.
>> So I did:
>>
>> $ mkvmerge -o goodsync.mkv -y 23456:0,77346/77340 outofsync.mkv
>>
>> I hope this helps.
>>
>> Doug
>
> thanks for the info, I'll give it a try,

Hadn't had a chance to try this yet but noticed that a cut I did of
the Xmas SNL episode had drifted out of sync. Just curious...you
mentioned that an episode you transcoded was .2 seconds out of sync by
the end. How the heck did you calculate it was .2 seconds? My eyes
aren't that fast. :-)

I never had this issue with the myth lossless transcode. Still curious
how it broke in .26.


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