[mythtv-users] Hardware for Best TV-Out?

[Mark Wormgoor]

Hi,

>>> > I´m currently using a gf4mx with a selfmade vga2rgb converter
>>> > (http://www.nexusuk.org/projects/vga2scart/) which is giving me uber-
>>> superb
>>> > quality on the frontend and good quality @watching recordings.
>>>
>>> I just installed my box with this cable:
>>> http://www.idiots.org.uk/vga_rgb_scart/
>>> I built my machine with a 9200SE for this purpose.  And I must say, the
>>> image looks absolutely stunning on my 32" Philips tv.
>>>
>>> Kind regards,
>>>
>>> Mark
>>
>> Just out of interest do you feel like having full resolution on your
>> recordings? As my livetv/recorded shows are just not that great as the
>> gui
>> is, even the osd looks definitely worse than anything in the gui
>> (video-epg
>> e.g.) It just feels like its missing some lines or doing some
>> interlace->deinterlace-> Interlace conversion (no deint filter).
>
> Most channels (and recordings) look great; no problems.  But I do have a
> problem with one channel and have just turned off transcoding to see if
> that makes a difference.  The osd looks good as well.
> I did not turn on deinterlacing, since I have not yet figured out how to
> get the display on my tv with progressive scan.  Will need to figure that
> out (if my tv supports it).
>
> And I just played a part of a dvd and it looks stunning, just as it did
> with my RGB dvd player (without progressive scan).
>
>> Which capturecard/resolution/modeline? Pal or ntsc?

I spent some time looking up the PAL standard and converting that into a
ModeLine.  I came up with this one, which is nearly perfect in its
timings:
    Mode "720x575pali"
	DotClock 13.875
	HTimings 720 744 808 888
	VTimings 576 580 585 625
	Flags "Composite" "Interlace"
    EndMode

Issues I have yet to figure out:
- can I use an uneven number of lines in interlaced mode?
  Will that give me troubles?
- if I use an uneven number of lines for porch or sync length in vertical,
  will it alternately use 2 or 3 lines, or will it use 2.5 (PAL standard!).
- the back porch for the horizontal line is a bit too long
  (5.766us, but it should be between 5.5 and 5.7), but I haven't seen
  troubles by this.  Everything else is within the PAL specs.

For those who take interest in the calculations.  PAL standards:
Line period 64 us (Micro-seconds)
Line blanking 12.05 +- 0.25 us			Front + Sync + Back
Line sync 4.7 +- 0.1 us				Sync
Front porch: 1.65 +- 0.1 us			Front porch
Burst start 5.6 +- 0.1 us after sync start.	Back porch

Vblank Start = 2.5 lines
Vsync Width = 2.5 lines
Vblank Width = 25 lines

Horizontal calculations:
Freq = 13.875 * 10^6 / (625 * 888) = 25Hz (Perfect!)
line period = 1 / (25 * 625) = 64us (Perfect!)
front porch = 744-720/888 * 64us = 1.730 us (between 1.55us and 1.75us!)
sync period = 808-744/888 * 64us = 4.6126s (between 4.6 and 4.8us!)
back portch = 888-808 / 888 * 64us = 5.766us (too high!)

Kind regards,

Mark
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* |\    /|      |  /|  /       Mark Wormgoor                  *
* | \  / |      | / | /        mailto:mark at wormgoor.com       *
* |  \/  |ark   |/  |/ormgoor  http://www.wormgoor.com/mark/  *
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