[mythtv-users] Loosen auto-swap from interlaced to progressive, but not vice versa?

Yeechang Lee ylee at pobox.com
Tue Feb 24 23:49:08 UTC 2009


I'd like to revisit an issue that has come up several times over the
years.[1] The issue is video streams with both interlaced and
(allegedly) progressive frames, and the problems such mixing causes.

As Daniel Kristjansson points out while closing ticket #2429, the real
solution is for broadcasters to not send out such abominations in the
first place. In my experience, though, the problem isn't so much that
mythfrontend doesn't deinterlace frames mistakenly marked as
progressive. It is that in many cases interlaced and progressive
frames alternate so quickly that mythfrontend is constantly jumping
between interlacing and not.[2] This is where the real problem with
playback comes from. As far as I know no one out there puts interlaced
frames in otherwise progressive streams but the other way around is,
again, far too common.

Mark Kendall suggests
(<URL:http://www.gossamer-threads.com/lists/mythtv/users/271909#271909>)
loosening the number of frames before mythfrontend detects a change in
frame type and switches to the other mode. Unfortunately, this means
that once mythfrontend is indeed in progressive mode, it takes that
much longer to switch back to deinterlaced mode.

Would a staggered approach work? What I have in mind is that
mythfrontend should very quickly switch to interlaced mode (currently
the criteria is two frames) if it sees an interlaced frame, but that
once there it should be much harder--10X, 20X, or more frames--to
switch back to progressive mode. I took a quick look at
NuppelVideoPlayer.cpp, but the relevant section (based on Mark's
comment in the above thread) quickly defeated my meager coding
skill. If my suggestion has merit, I hope someone else can take up the
burden.

Another approach is to make it possible for deinterlacing to be
settable for each channel, but that would require a change to the
database schema. (The last comment in #2429 mentions that "profiles in
0.21" might implement this already, but I don't know what this refers
to. I would highly welcome anyone pointing the obvious out to me,
though!)

[1] Often enough that Mike Dean was able to point to four different
threads about it
(<URL:http://www.gossamer-threads.com/lists/mythtv/users/225631#225631>)
back in September 2006!

[2] In my case, NBC and premium-movie cable channels are notorious for
this.

-- 
Yeechang Lee <ylee at pobox.com> | San Francisco CA US


More information about the mythtv-users mailing list