[mythtv] render2019: step-length oddities in video editing

[Mark Kendall]

On Sun, 6 Oct 2019 at 12:48, John Pilkington <johnpilk222 at gmail.com> wrote:
>
> I use the editor to establish cutpoints in almost all my recordings,
> cutting at keyframes.  In 2019render 33b109b1106e the static images
> shown at keyframes are often blurred, but stepping forward and back by
> keyframes is consistent.

There is no reason that images would be blurred. The only change in
behaviour I can think of is that the render branch code will
deinterlace the 'pause' frame when it can/should (i.e. interlacing is
detected and deinterlacing is enabled).

I may need to check exactly what is happening with some of the more
advanced deinterlacers to make sure we get the correct frame when
multiple reference frames are needed - but I *think* they should be
OK:)

> Nominal 1-frame steps forward are OK, and advancing around 7 frames
> usually gives a better image; but steps back are by keyframe intervals.
> Nominal 0.5-second steps do the same, and nominal 1-second steps seem to
> go to keyframes in both directions.  The larger steps aren't exact, but
> near enough.
>
> I've tried this with both h264 and mpeg2 recordings.  I haven't done a
> direct comparison with master, but the feel is different.

I noticed some time ago that frame by frame seeking was
inconsistent/erratic. Seeking forwards seems to often jump a little on
the first seek and then works OK. Seeking backwards is much worse.
David mentioned it a while back on IRC and believes it is a fairly
long standing regression in master. There may well be other issues in
the render branch of course:)

Thanks and regards
Mark