[linux-dvb] Re: DivX player for DVB system?

[Stephen Davies <steve@daviesfam.org>]

On Wed, 18 Jul 2001, Henning Holtschneider wrote:

> Another option that I have been thinking about for a while is using a VGA 
> card with TV-out and the Linux framebuffer driver. Does anyone have 
> experience with Matrox cards (they seem to be supported best by the 
> framebuffer driver)? What about the image quality? I currently have an ATI 
> card but the framebuffer driver won't run below 59.9 Hz refresh rate when 
> the card is connected to my TV and the image quality is awful (yes, I know 
> that 640x480 will never look as sharp on a TV 352x288 TV screen as it 
> should).

I've got some experience.  My experience was that setting up TV out from
modern video cards was much more fuss than I expected.

In theory, two main approaches:
 1) Use RGB to your TV via SCART/component, program your video card for
    PAL/NTSC rates.  Simple VGA->SCART cable with a couple of components
    to make composite video does the job.
 2) Video card with BT869 chip on board, composite/s-video output to TV

For the first, few (no?) modern cards can do low enough rates to do
PAL/NTSC, and most don't support interlacing.  I can't find a single one
that can do the rates and interlacing and also supports XVideo.  And, of
course, older cards are slow, don't have xvideo/video accelaration etc.

For the second: the Matrox G450 video out isn't supported on X.  The G400
is supported but is hard to buy now.  Additional problem is that XVideo
doesn't work on the second head- which drives the video output.

I ended up using a Voodoo 3 card with TV out that I already had.  I made a
patch for the lmsensors bt869 driver to do 720x576 with overscan - so
right for DVD output "full screen".  This mode has the advantage that no
vertical or horizontal scaling is needed, hopefully optimizing the
display.  I disable flicker compensation for video out as it reduces
vertical resolution, and is unnecessary for video output.

This produces a subjectively good picture for video (mpeg1/2 at 720x576
is what I usually use) - main issue I have is that the XVideo
frame refresh isn't synchronised with the display refresh so a horizontal
tear is sometimes visible on some scenes.

Don't judge the video output by a "data display" - judge by displayed
video; subjectively the first looks poor - flicker as a result of
interlace artefacts, video bandwidth limits, etc.  But video looks good.

I would have used DVB except that there is essentially little to be
received "off air" suitable for an English speaker.  And the DVB cards are
rather limited for playback, as seen in this thread.

Hope that is helpful,
Steve Davies




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