[mythtv-users] HD deinterlacing

Seth Daniel mythtv.org at sethdaniel.org
Mon Oct 1 18:57:55 UTC 2007


On Mon, Oct 01, 2007 at 11:48:15AM -0700, Jon Boehm wrote:
> 
> 
> Ryan Steffes wrote:
> > On 10/1/07, Tom Dexter <digitalaudiorock at gmail.com> wrote:
> >> On 10/1/07, Phil Vid <phil.vid at gmail.com> wrote:
> >>> Using bob, it feels like the video is slightly sped up at times. When
> >>> there is no motion, it seems fine but then when a scene change occurs
> >>> it seems like things speed up slightly even though the audio sounds
> >>> fine.
> >> I've been using bob for quite some time with my RP CRT TV.  Since my X
> >> is outputting 1080i doing so required the unsupported change described
> >> here:
> >>
> >> http://www.gossamer-threads.com/lists/mythtv/users/285404#285404
> >>
> >> Only recently I started noticing the slight speed-up of video like
> >> you're describing, though it seemed in my case to be specific to NBC
> >> HD broadcasts.  Just as you describe, the video would speed up
> >> temporarily without disturbing the audio.  In some cases it would
> >> happen when jumping forward or back, as though the specific keyframe
> >> it was starting from made a difference.  I never used to see this at
> >> all and it doesn't occur with other deinterlacing methods.  However,
> >> it appears that I've found a way to correct it.  Today I had an NBC
> >> recording where I could reproduce this issue.  I tried adding "+hsync
> >> +vsync" to the end of my mode line and now I have no problems with
> >> this using bob.
> >>
> > 
> > Did your recording show the correct length?  I've noticed a problem
> > that I haven't started to track down where recordings (again,
> > predominantly NBCHD, which is why I asked) have periodic burst of
> > faster motion.  The length of the show itself shows as being shorter
> > than it should be, though.  For example, an hour long show may show as
> > being 53 minutes long and when watching it, there's occasional bursts
> > of slightly sped up video.  It's not particularly annoying to me, so I
> > haven't really started figuring out what's going on; I watch most
> > shows at 1:1.15 anyway.
> > 
> 
> Thought I would chime in here.  I have noticed this behavior.  However 
> mine is not with NBCHD it is with CBS_HD prime time.  The program length 
> is usually 5 to 7 min shorter than reality.  ( As an aside, Lettermen 
> later in the evening doesn't have this problem.)  Usually the visual 
> artifacts shows up when returning from a commercial break.  I've noticed 
> that turning off Opengl vsync fixes the slowdown/speedup problem.  In 
> addition, I've noticed that BOB is not keeping up with these problem 
> recordings.  I see the interlacing artifacts during rapid motion 
> possibly in relation to a scene change.  I can tell BOB is working since 
> I can see the vertical hopping on occasion, but it just not keeping up.
> 
> I wonder if Comcast or the local affiliate are messing with the CBS 
> stream, or if my HDHomeRun is having problems with the QAM steam.

http://www.gossamer-threads.com/lists/mythtv/users/265138?#265138

Apparently some stations (notably CBS and NBC here in the States)
broadcast commercials at a different encoding.  This fools Mythtv into
displaying the wrong run time.  I think this also affects the speedups
you are seeing (and I am also seeing...typically directly after a
commercial break (at least in my case)).

-- 
seth / @sethdaniel.org
I either want less decadence or more chance to participate in it.


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