[vdr] Re: choosing a FF card

[Tony Houghton <h@realh.co.uk>]

In <420A3266.9020702@f2s.com>, Ian Molton wrote:

> Tony Houghton wrote:
> 
> >Too large for what? ICBW, but my understanding is that if a device is
> >outputting 576 lines in PAL, the height is fixed by the TV and can't be
> >controlled by the device, except that it can probably be shifted up and
> >down a bit. Then the device has to fill the horizontal field, including
> >overscan, to make sure the aspect ratio is correct.
> 
> The overscan is the part of the picture thats displayed offscreen such 
> that blooming and other distoprtions present in the garbage TV tubes we 
> have dont encroach so visibly on the picture.
> 
> The amount of overscan is determined by the timings of the video mode 
> you present to the TV, not the number of pixels per row or number of 
> lines. with analogue TVs (or monitors) there isnt any defined 1:! 
> mapping of pixels on screen to pixels in the framebuffer and its not 
> uncommon for poorly adjusted TVs and monitors to have half pixel 
> overlaps or worse between pixels, etc.
> 
> >If a graphics card is showing an 800x600 desktop on a TV with no
> >overscan, then it's probably scaling to fewer than 576 lines. If you're
> >only concerned with video, then I think you'll find the amount of
> >overscan is the same as you'd get from a DVD player or STB.
> 
> Im displaying a pal res output, 576 lines. but the amount of overscan in 
> the timings produced by my board is both too great and unadjustable.

That surprises me. The way I understand CRT signals work I would have
thought the only way you can change the height of the picture is to
change the number of invisble lines, and on a TV the total number of
lines is fixed. Are you sure your framebuffer is 576 lines and you're
getting more overscan than from other sources?

> >>3) Is the TV output properly interlaced? what about when playing a DVD 
> >>which is progressive-scan (most movies) ?
> >
> >
> >I don't know about FF cards, but my DXR3 handled both extremely well,
> >although I had to use it in NTSC mode for NTSC DVDs. AFAIK FF cards are
> >better than the DXR3 in terms of scaling non-standard sizes and
> >displaying an OSD.
> 
> So how does the card do the re-interlacing for progressive scanned 
> material? (do they all use some standard algorithm?)

I would have thought all you'd have to do is show half the lines from
one source frame in the first output frame, then the other half in the
second output frame.

> >>basically, I want really really good TV output from both DVB and DVD, 
> >>possibly divx (how does that work on these cards?) too.
> >
> >DivX has to be converted to MPEG1 on the fly. You've got an EPIA system
> >haven't you? You might well not have enough CPU power. And what's wrong
> >with the CLE266?
> 
> well the epia decoder works very well. what doesnt work so well is the 
> chrontel tv encoder in the thing which gives a low quality, noisy, 
> non-frame-parity-aware output. if only my TV had RGB progressive input...

So the CLE266's MPEG decoder can't do field parity? That's poor. Have
you got a spare PCI slot? Your best option may be to use a DXR3 for TV
and other MPEG 1/2, and your CLE266 for DivX etc, with a SCART switch
box. I don't think interlacing is ever used on anything but MPEG2.

-- 
TH * http://www.realh.co.uk