[mythtv-users] Transcoding without losing commflagging

f-myth-users at media.mit.edu f-myth-users at media.mit.edu
Thu Sep 18 03:53:44 UTC 2014


Suppose I have an SD-quality recording (PVR-x50 MPEG-2) that I run
through Handbrake to transcode into h264.  Is there any sensible way
to either (a) retain the commflagging, or (b) regenerate it?  Details
follow.

(a) Yes, I know that the existing recordedmarkup data will be all
kinds of wrong after transcoding.  Is there some way of convincing
Handbrake to give me a list of input & output frame numbers or byte
positions, perhaps via some debug flag?  One could conceivably update
recordedmarkup with this data, hence preserving commflagging, and at
some level, Handbrake knows this data.  (I know that it probably can't
be frame-accurate no matter what, but even close would be acceptable.
Obviously I can't just use a constant divisor the input & output rates
vary.)

(b) If I were to clear the commflagging data and regenerate it, what
formats can Myth inhale?  Should the output file be written as mp4,
mkv, or something else?  Are there known bugs in commflagging that
might prevent this from working?  (I assume that "any file that
mplayer can play" is too general.)  I recall hearing all kinds of
bugs and edge cases having to do with flushing and regenerating
recordedmarkup or commflagging, but I don't know how well Myth
currently behaves, or what's planned---if Myth is supposedly going
to keep around multiple transcoded versions for different types of
devices, how is commflagging going to interact with that?

These questions are theoretical so far---I'm not running current Myth
to test (b), and (a) likely would require a DB hack that I'm sure
would lead to "you're on your own" responses re the data therein even
if I could get the data.  But I'm evaluating some approaches here.

Thanks!

P.S.  "Cut first, then transcode" unfortuately isn't an option here;
I'd like to do this for video without human intervention, and
commflagging is nowhere near good enough to risk transcoding its
output unseen and throwing away the original.


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