[mythtv-users] Alternatives to lossless transcode

Karl Dietz dekarl at spaetfruehstuecken.org
Wed Nov 13 21:08:12 UTC 2013


On 13.11.2013 10:43, mark wrote:
> Sorry my mistake. I assumed that if I ran just mythtranscode --fifodir
> it would just output the two streams in their entirety to the nominated
> files. Trying your script now, for some reason my ffmpeg did not like
> the '-profile high' switch but have taken that out and it works.
>
> The audio was much more in sync than previously, but it still just seems
> a little off. I ran mythDVBcut over the same file (which uses ProjectX
> and no mythtranscode) and the file generated by your script had a delay
> of 80ms (from mediainfo) versus 112ms from the ProjectX version. I'm not
> sure that -hand on heart- I could pick a difference in sync of 32ms but
> it did seem just that little bit out whereas the ProjectX file just
> seemed spot on.

I think the difference in sync comes from something else in the
processing chain and can not be seen in the difference of "delay".

Your version of mythtranscode (looking at the logfile from the 6th) has
known bugs in the handling of audio (avf and fifo mode) and video
(lossless mpeg2 mode) timestamps that got fixed a bit less then 2 days
ago in fixes/0.27 so it may be worth to update to the latest nighly and
retest with the recording in question (if you still have it around)
See 
http://code.mythtv.org/cgit/mythtv/log/mythtv/programs/mythtranscode?h=fixes/0.27


The delay information from mediainfo appears to be the delta of the
first audio audio timestamp and the first video timestamp. (found that
out by searching their bug tracker, documentation is hard to find) As
audio and video frames have different durations depending on how you
cut away excess frames at the beginning you'll get different delays.

Regards,
Karl


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