[mythtv-users] How I got great quality TV-out on my nVidia MX4000

[Will Dormann]

Brian J. Murrell wrote:
> Hrm.  Optimal meaning "as good as it can get with this card but not
> quite ultimate?", or do you believe you have a TV-Out signal that
> represents how the content was originally broadcast (i.e. perfectly
> interlaced fields)?

"optimal" meaning the best quality out of the nVidia card using the 
various combinations of options that I have used.   Not quite as good as 
broadcast quality.  (Or possibly the PVR-350)


> Which is just a regular old interlaced 59.94 fields/s TV right?  Is SDTV
> "Standard Definition TV"?

Yes.


> Why de-interlace?
> 
> Why not send the interlaced recorded signal you recorded back to the TV
> in the format that it expects to be played in, interlaced, with each
> field being shown for 1/59.94th of a second instead of combined with
> another field and only shown for 1/29.97th of a second.

 From what I've gathered, the nVidia cards (or pretty much any other 
computer video card) won't retain the original recording's interlacing. 
  Dedicated hardware such as the PVR-350 is required for this.    I 
could be wrong, though, so feel free to correct me.

XvMC + Bob gives me a better resolution picture than XvMC + No 
Deinterlacing.   I'm not sure why this is, but the difference is pretty 
clear.   Interestingly enough if I'm not using XvMC, no deinterlacing 
give me the better quality picture and Bob gives me something that looks 
like 1/2 the vertical resolution is lost.  (The opposite results).  I 
had a sample video segment that had some text and some diagonal lines. 
In the "low vertical resolution" mode (either XvMC w/ no deinterlacing 
or non-XvMC with Bob deinterlacing), the diagonal lines would have a 
stairstep appearance.   Also, the text of the OSD would be very blocky. 
  Toggling the deinterlace option would make the picture (and OSD) look 
right again.

I've read that the Bob deinterlacing for XvMC is completely different 
code than the Bob deinterlacing without.  So perhaps that has anything 
to do with it.

Now that I think about it, I wonder if it's a field order issue?   I'm 
not totally certain how the Bob deinterlacer in mythtv works, but let's 
say that it pushes the top field down by a half line and the bottom 
field up by a half line.  If the field order is reversed, then it's 
pushing the top field up by a half line and the bottom field down by a 
half line.  (Which could possibly explain the stair-stepping of diagonal 
lines and resolution loss in the OSD)  If so, I wonder if it's possible 
to reverse it somehow?    Or then again, maybe I'm just seeing this:
http://mythtv.org/bugs/show_bug.cgi?id=167
(though in my case, it's not a jitter up and down, it's an obvious loss 
of resolution)


-- 
-WD