[mythtv] GOP_BYFRAME vs. GOP_START and mythcommflag --rebuild

Doug Larrick doug at parkercat.org
Tue Jun 5 00:06:38 UTC 2007

Is there a reason that avformatdecoder creates positionmaps using
MARK_GOP_START (using keyframe number, assuming a fixed keyframe
interval) rather than MARK_GOP_BYFRAME (using frame number) by default?
 Maybe non-avformatdecoder playback needs the other format?

When using mythcommflag --rebuild on an ATSC-sourced MPEG2 recording,
this results in a totally broken positionmap, since ATSC keyframes come
in at irregular intervals.

I've "fixed" this in my local tree by hardcoding the affected function
(AvFormatDecoder::OpenFile) to always use MARK_GOP_BYFRAME but I'm
wondering if there's a more general way to fix the problem.  Currently
it chooses BYFRAME for avi files; perhaps it should do so for transport
streams as well?  Or for everything?

Thanks for any comments,

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