[mythtv-users] Ultimate Mythtv vid card, part II

[papenfuss at juneau.me.vt.edu]

On Mon, 9 Feb 2004 steve at nexusuk.org wrote:

> On Mon, 9 Feb 2004 papenfuss at juneau.me.vt.edu wrote:
> 
> > good flicker-full  output for the best video.  I, personally, would rather 
> > fudge the UI a bit (anti-aliased multi-line horizonal lines, for one) so it 
> > looks acceptable without flicker reduction.  
> 
> Since I plug my TV directly into the VGA connector on my PC I have 
> absolutely no image processing to reduce flicker, etc.  

	Directly into the VGA connector?  Is this a progressive TV or have you 
cooked up a NTSC/PAL output for the vid card? 

Yeah there are a 
> few bits of the frontend that flicker, and if I was selling it as a 
> commercial product I'd want to fix that but for my personal use it's not 
> enough of a problem for me to care about.  You're absolutely right though 
> that the way to fix this is to to a bit of antialiasing between vertically 
> adjacent pixels.  

	Exactly... It's not worth the bother at this point... I'd rather have 
the GUI be a little flickery than compromise on video quality.  It just annoys 
me when the vid card manufacturer/driver assumes, "It'll be different when it 
flickers, so throw away every other line to make it look good for the 
consumer."


One thing I'd love to see (and maybe I'll get around to 
> writing it myself eventually) is a "deinterlace on pause" feature so when 
> I pause a video (or play it in slow-mo) it deinterlaces the frames so it 
> doesn't flicker between the two fields.

	So this would be the deinterlace playback without having to have it on 
all the time, right?  Is that an interpolation process right now?

> 
> > 	You should be able to code up a modeline for anything you want (save 
> > the interlace).  It's not a direct link to the output on the TV, but it'll let 
> > you overscan, etc.
> 
> Certainly with the binary drivers when you're running with the TV output 
> turned on, setting anything other than a "standard" mode results in X 
> exiting with "Not a TV mode" or words to that effect.

	OK... I stand corrected.  What a pain in the butt though.  I just with 
NVidia would get over themselves and let the source/specs out.  They appear to 
have won the video card game already anyway... why not make linux folks 
happier?

> 
> > MPEG (YUV) -> VGA (RGB) -> YUV (transcoder to TV) -> RGB (guns on TV).  
> 
> I've never understood what the point is in doing YUV over separate cables 
> - in composite video then it all makes sense because you transmit the 
> luminosity (Y) at high resolution and the colour (UV) at low res.  It 
> saves bandwidth and isn't a problem because your eyes are pretty 
> insensitive to colour.  But if you have separate cables for each component 
> then you're transmitting all 3 at the same resolution so I can't see any 
> advantage over just using plain RGB...
> 
	There is, in fact, a fair bit of *disadvantage* in doing this from a
quality perspective.  It was purely an implementational decision.  All TV's
would already have YUV->RGB separation circuitry since in the end they have to
drive RGB guns with a YUV signal.  S-Vid just bypasses the separator.  I'm
pretty sure that they don't even allow for more bandwidth on any of the
channels than composite... it's just that it's easier for the TV to get all the
information without fancy adaptive comb filters, etc.  It basically removes
artifacts like dot crawl, color blooming, high-frequency Y/C interference
(think Letterman's tie), etc.  Doesn't inherently make the picture sharper.

  Pretty cool to look at the composite vs. svid on the scope though.  I did
that when I was tweaking my homebrew NTSC encoder card.  Looking at a horizonal 
line on the standard colorbar test pattern looks like this:

Composite:

               /\/\
              |     /\/\
              |          /\/\...
__    __/\/\__|        
  |__|



S-Video:
(Y)
               ____
              |     ____
              |          ____...
__    ________|        
  |__|


(C)
________/\/\___/\/\ /\/\ /\/\...


	Where the /\/\ is the colorburst and U/V channels modulated on the
high-frequency color subcarrier (3.58 MHz NTSC or 4.43 MHz PAL).

-Cory
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