[mythtv-users] Help with interlaced DVI output configuration

jason maxwell decepticon at gmail.com
Thu Mar 22 12:47:06 UTC 2007

I have also found flaws with the quality of deinterlacing that myth
currently provides, and have hit similar roadblocks. I'm not so
unhappy that I cant live with it, but the occasional combing does get
on my nerves. Especially because I specifically built an overkill
system to ensure the best quality HD playback, but still cant match
the TV's built in deinterlacing. I thought TVs scalers/deinterlacers
are on the low end, and that's why a lot of videophiles use
standalone processors. Surely those algorithms in use on the quality
processors would be available programmatically, no? Maybe the demand
isn't high enough for someone to put the effort in to implement them
in myth.

On 3/21/07, Chris Weiland <hobbiticus at gmail.com> wrote:
> I've searched and search and can't seem to find a definitive answer to my
> questions, so hopefully the all-knowing body of the mythtv discussion list
> will know.
> My Situation:
> I've got a 32" Samsung LCD TV that has a native resolution of 720p.  I have
> a cable box with an HDMI output that I've hooked into my TV's HDMI input in
> the past, which resulted in a very clean and crisp picture.  I guess I can't
> be 100% sure that it was outputting in 1080i, but it says it was.  My myth
> box is setup to run at the 720p resolution, outputting over the DVI
> interface on my geforce 6200, through a DVI-HDMI cable, into the HDMI input
> on the TV.  As you might suspect, playing 1080i content without
> deinterlacing is filled with interlacing artifacts.
> My Problem:
> I'm very sensitive to even the slightest visual artifacts, and none of the
> built in deinterlacing methods in mythtv are as good as I would like it to
> be.  So, logic along with searching through lots of mailing lists suggests
> that if I can output 1080i from my myth box, the (much better) TV
> deinterlacer/scaler will kick in and give me the same crisp and clear images
> that I get when I hook up my cable box directly.  This should theoretically
> also save CPU cycles in the deinterlacing/scaling that myth is currently
> doing.
> The Solution:
> Output in 1080i! (and turn off mythtv's deinterlacing)
> So, first of all, am I correct in everything I've mentioned above?
> I'm not exactly sure how to go about doing this.  My TV's EDID info says
> that it will accept 1080i sources, and the nvidia
> driver seems to have the 1080i modes built in.  However, if I try to use the
> 1080i modes, the X log complains that the vsync is out of range.  This is
> "true" because the TV wants 60hz, but the mode is listed as 120hz.  So, I
> turn off the vertical sync mode validation.  Now it says that the 1080i
> screen size is bigger than the LCD's native resolution.  Fine, so I turn off
> the DFP native resolution mode validation.
> Now it works!  Except not.  X accepts the 1080i video mode, and the change
> is apparent on my TV because it is only showing the top half of the screen,
> and the horizontal scan lines are out of sync.  It's a little hard to
> explain, but it's almost like instead of drawing lines 0,1,2,3,4... it's
> drawing lines 1,0,3,2,5,4..., except making each scan line twice as big, so
> the screen only shows half of the picture.  I couldn't think of what to do
> after that.
> I also see that I can define a custom modeline.  I had to do a lot of mode
> validation disabling to get this to work too.  I have to admit that I havn't
> played with this too much, but I can't get the driver to like anything that
> I create.  I think once I finally got X to start using my modeline, all I
> got was a blank screen.  That's where I gave up.
> I've seen elsewhere that interlaced modes over the DVI output stopped
> working after driver version 6629, but that driver doesn't support the 6200
> card.  However, this was from a post back in 2005, so hopefully that's not
> the case anymore.  I've also seen some people say to enable TwinView with
> only one display device connected for some reason, but no one ever explained
> what settings they used for that.  Others have said that I need to turn off
> some vsync settings in the nvidia-settings program.  I havn't investigated
> these issues myself yet, so hopefully someone can tell me so I don't have to
> waste my time.
> _______________________________________________
> mythtv-users mailing list
> mythtv-users at mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

More information about the mythtv-users mailing list