[mythtv-users] Strange inerlace problem using ATI rage128 -> NTSC transcoder -> TV

[Gregory E. Porras]

Hello all, this is my first post to the list, so bare with me.
I've been running Myth since September of last year and so far
we love it.

My system is currently as follows:
- Intel D865PERL 2.4GHz P4 with 512meg
- 2 PVR250's and 1 PVR350 (not using TV out)
- GF-FX 5200 using SVIDEO TV OUT
- 4 hard drives LVM'd together, XFS as filesystem, DMA is ON for all 4
- FC1 that has been "apt-get dist-upgrade" (recently reinstalled from
RH9 using jarrods guide)
- The Myth RPMS currently installed via apt-get are: 
	mythtv-theme-photo-4-5.at
	mythdvd-0.15-31cvs.rhfc1.at
	mythtv-theme-sleek-0.35-1.at
	mythtv-backend-0.15-67cvs.rhfc1.at
	mythgallery-0.15-52cvs.rhfc1.at
	mythtv-theme-visor-0.13.1-3.at
	mythweb-0.15-52cvs.rhfc1.at
	mythtv-suite-0.14-37.at
	mythtv-0.15-67cvs.rhfc1.at
	mythtv-theme-gant-0.pr1-1.at
	mythtv-frontend-0.15-67cvs.rhfc1.at
	libmyth-0.15-67cvs.rhfc1.at
	mythweather-0.15-49cvs.rhfc1.at
	mythnews-0.15-22cvs.rhfc1.at
	mythtv-themes-0.15-67cvs.rhfc1.at
	mythtv-theme-purplegalaxy-0.20031214-2.at
	mythvideo-0.15-48cvs.rhfc1.at
	mythgame-0.15-51cvs.rhfc1.at
	mythmusic-0.15-52cvs.rhfc1.at
	mythmkmovie-1.0.1-3.rhfc1.at
	mythbrowser-0.15-16cvs.rhfc1.at

All this is working great for us... but, I am a perfectionist and 
would like to fix one last nagging problem with the video 
output: interlacing artifacts.

It all started with this thread http://www.gossamer-threads.com/perl/mailarc/gforum.cgi?post=103525
This describes a VGA to NTSC transcoder, but requires a video card that
can generate true NTSC interlaced signals.  Well I ended up purchasing
an ATI rage 128 card as well as taking the easy road and purchasing
the evaluation board from Analog Devices.

The picture quality is indeed excellent even on the GUI,
but I am ending up with yet another interlace problem.

I have interlacing artifacts only a percentage of the time.
If I play video under Myth at 1/16 speed to see frame by frame,
I see interlacing every 2 of 5 frames.  So 2 frames with horrid
interlacing, and 3 rock solid frames. 

I've tried twiddling the modelines, using composite as opposed
to svideo, and it makes no difference.  I saw somewhere a suggestion
to turn on experimental A/V sync in myth, but still no help.


The relevant sections of my XF86Config are:

Section "Monitor"
    Identifier  "NTSC"
    VendorName  "Canada/USA/Japan"
    ModelName   "Televison"
    DisplaySize  400 300
    HorizSync   14-29
    VertRefresh 50-60
                                                                                
    ModeLine "NTSCspec-59.94i" 14.318 768 784 848 910 483 484 492 525 Interlace -HSync -VSync
EndSection
                                                                                
Section "Device"
    Identifier  "Videocard0"
    Driver      "r128"
    VendorName  "Videocard vendor"
    BoardName   "ATI Rage 128 Pro Ultra"
EndSection
                                                                                
Section "Screen"
    Identifier "Screen0"
    Device     "Videocard0"
   Monitor     "NTSC"
    DefaultDepth     24
    SubSection "Display"
        Depth     24
       Modes   "NTSCspec-59.94i"
    EndSubSection
EndSection
                                                                                

What could I possibly be doing wrong?


Thanks
Gregory