Hi, "Nemosoft Unv." wrote: > > 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 :) Yeah, but for the subtopic of even and odd lines I agree with Jonathan, which answered a little later. And the question is already, what is the resolution of the picture xawtv delivers. Not all 625 lines are represented in xawtv's window (I think because of the vertical sync impulse inside the FBAS signal), but which is the exact number of lines, are it really 575, is this number constant when changing from station to station or does it change, and how much pixels per line are depicted horizontal ? Is it possible to get exact values ? > > > 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). Syncing would be the best resolution IMHO, but I'm in doubt that this could be realized. > > 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. When syncing could not be realized, would it be better to tweak an X11 mode with an even multiple vertrefresh of the TV vert framerate (say 100 Hz because of the capabilities of most monitors) or does this not matter at all ? > > > 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. Exact:-). All 100Hz TV's (which do a double buffering to realize this doubling of the vertical framerate) incorporate a kind of motion compensation to reduce/eliminate this kind of distortion, and it seems that this could also be done in software (Dscaler) > > 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. The load on the PCI/AGP bus, another point, even when we see todays discussion of Bugs in VIA's Southbridge regarding higher loads on the PCI bus. Wouldn't it then not be the better way to use the least possible fullscreen resolution, either for minimizing the busload and for minimzing the timeoffsets between even and odd lines ? > > > Could anybody please shed some light over this questions ? > > Hope this clarifies. Not complete, further discussion required for further clarification ;-) > > - Nemosoft > > ----------------------------------------------------------------------------- > Try SorceryNet! One of the best IRC-networks around! irc.sorcery.net:9000 > URL: never IRC: nemosoft IscaBBS (bbs.isca.uiowa.edu): Nemosoft > >> Never mind the daylight << > > _______________________________________________ > Video4linux-list mailing list > Video4linux-list@xxxxxxxxxx > https://listman.redhat.com/mailman/listinfo/video4linux-list
