[mythtv] hardware questions

[Erik Arendse]

At 31-12-02 19:15, m0j0.j0j0 wrote:
>Can you clarify "reasonably happy" regarding the TV-Out? I'm wondering
>if I'm better off just buying a VGA-TO-NTSC converter than messing
>around getting TV-Out card like the G200 working.

Just my 2cts (well, maybe some more :-):

In order of improving quality your possible connections are:
- modulated RF (using an external antenna connection, tuning your TV to the 
correct channel)
- composite (in Europe 21-pin scart switched to composite mode, or a single 
small coax plug, BNC connector on professional equipment)
- Y/C separated, also called S-video (in Europe a 8 pin small plug, or 
21-pin SCART switched to Y/C mode, I think in the US a small 4 pin plug?)
- component or RGB (In Europe 21-pin SCART connector switched to RGB mode, 
or 3 BNC coax-connectors on professional equipment, I think in the US 3 
colorcoded small coax plugs?)

Where you can choose between NTCS and PAL:
- NTCS has higher framerate, better for video sourced material
- PAL has higher reolution
- PAL has 50 herz framerate, better for cinema sourced material
- PAL is more stable (difference is lot less than 20 years back), not an 
issue with component video

If in practice you experience any other order, it is related to different 
quality equipment. Meaning a good composite output on a computercard over a 
modulator could even beat a lousy Y/C output on a cheap card.

Secondly sometimes the output levels on computercards are wrong, or you 
have overscan/underscan or framerate issues. All of these are correctable 
with a cheap external modulator, leading to an improved experiance of quality.

The theoretical and practical maximum quality attainable can only be had 
with component video, and the Matrox G400 is the only affordable card I 
know personally wich outputs a (correct level, framerate and  lines) RGB 
signal. I don't know about the G200 firsthand though, but maybe it can do 
the same. On the Matrox site you can find the pinning for the RGB cable you 
have to make to connect to the second head.

As a beside: nearly all VGA outputs can easily connect to a component input 
with only a few cents of extra components, but it is often impossible to 
get the chip working on the correct refresh and line speeds.

An other issue often overlooked is interlacing. If you de-interlace and 
play back on your 50 Hz (PAL) or 60 Hz (NTSC) TV, there will be by 
definition an information loss (funny enough this will be perceived by some 
people as a quality improvement, so by all means try out for yourself).
The first exception is a double scan TV, where the TV displays 100/120 Hz 
and is de-interlacing on its own, or if you can feed the TV with a 100/120 
Hz signal with you deinterlaxed yourself. In that case you keep all the 
information, but loose the raggedness and the flickering.
The second exception is cinema based source material, where there is no 
interlacing in the source and you can just interleave the framehalves you 
grabbed.

If you only have a normal interlaced TV, the best approach for a settop box 
would be to grab fullsize interlaced, and playback the same. Sometimes this 
is impossible as some grabbing hardware is just giving you two frame-halves 
without them having a defined relation in time (i.e. always even-first or 
odd-first. By the way: If somebody could prove me wrong here I would be 
very happy...).

Erik