Hello,
On 01-Jun-01 Gerd Bitzer wrote:
> Hi folks,
>
> when using xawtv in fullscreen mode with PAL and 625 lines, what would
> be the optimal mode for XFree ? I know that in ~/.xawtv every possible
> resolution which is also defined in XF86config could be used as
> fullscreen, but what's the optimum ? Shouldn't it be, that the setting
> of the videomode should be an exact match with the number of lines and
> rows of the TV picture ?
Not necessarely; but first, let me point out a few things:
- From those 625 lines, only 575 are actually used for the image
- The current bttv driver only captures even or odd frames, so only half of
those 575 lines are being used for display on your monitor, e.g. 287.5.
- The horizontal resolution is a lot higher, in the order of 600-700 lines.
So you´d have a really skewed mode :)
> And what about vertical refresh frequency, shouldn't it also exact match
> the vert. refresh of the TV pic, or at least be even multiplied ?
Preferably, yes. However, it is very difficult to get the things at exactly
the right time, and keep them in sync; it´s not unlike trying to mix two
discs on a turntable. What you want is that the bttv card is synced with the
refresh of your video card (or the other way around).
The bttv card should not write to video memory that is being displayed at
the moment, but that´s near impossible since the videocard reads the memory
2 to 3 times faster than bttv fills it.
> Last but not least, what about this f*cking interlace distortions when
> there is movement inside the picture, could this also be kind of
> optimised when an optimal videomode is used ?
You mean jagged edges in vertical lines when there´s horizontal movement
(like a panning camera)? Nothing you can do about it.
The only solution to this ´problem´ is double buffering on the VGA side. A
monitor simply isn´t a TV.
The only advice I can give you about this is: pick the maximum size that
your bttv card supports and does not produce artefacts when there´s heavy
change in the picture (not necessarely movement, color/brightness changes as
well). Remember, every pixel that changes has to be pushed through your
PCI/AGP bus.
> Could anybody please shed some light over this questions ?
Hope this clarifies.
- Nemosoft
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