[vdr] 1:1 pixel mapping - a waste of time?

Pasi Kärkkäinen pasik at iki.fi
Tue Jan 6 10:49:23 CET 2009


On Tue, Jan 06, 2009 at 01:17:52AM +0200, Jukka Vaisanen wrote:
> Yes, it's a good idea to get 1:1 pixel mapping on your display. Double
> scaling (first pc, then display) is not a good idea, ever. 
> 
> But, some problems arise:
> 
> HDMI uses DVI signalling for the video (and audio is hidden in a
> vertical blanking time slot believe it or not) so it may seem like just
> another connector.. however in their finite wisdom the HDMI
> standardization people decided that HDMI will not support arbitrary
> resolutions, but instead only the existing (and back then, planned)
> broadcast resolutions:
> 
> - 576i/p (pal) and 480i/p (ntsc)
> 
> - 720p (1280x720)
> 
> - 1080i and 1080p (1920x1080)
> 
> The world is full of TVs with 1366x768 and other weird resolutions.
> There are also plasmas with 1024x768 etc "standard computer
> resolutions". The big surprise to many people is that even though DVI
> signalling could carry these native resolutions, the displays themselves
> won't accept / sync to them. And they don't advertise them in the EDID
> data so you have to force your computer to that resolution / refresh to
> even try it (and fail).
> 
> The only true 720p displays I have seen are rear-projection TVs and
> data/av projectors. They will accept their native resolution of 1280x720
> over HDMI, however getting rid of overscan to get 1:1 is another
> matter..
> 
> Then a solution:
> 
> I used to have a Panasonic plasma with a similar non-standard resolution
> and I used the VGA port with it to automatically get a 1:1 pixel display
> as it's intended for PC display use. Yes VGA is not optimal but at that
> resolution and a 1 meter cable, who cares... Today I have a full HD
> 1920x1080 panel with an option for "exact scan" which gives me 1:1
> pixels (without overscan) out of the box over HDMI, I just run normal
> 1920x1080 at 60Hz out of my computers.
> 
> And finally a question:
> 
> If someone can tell me how to get 576i over HDMI out from VDR, please
> do. That way I could use my external HQV Reon video scaler to upscale
> it.. Of course it would need to allow me to switch modes for 720p and
> 1080i also based on broadcast resolution ;)
> 

Hello.

Please check this thread:
http://www.linuxtv.org/pipermail/vdr/2008-July/017347.html

Original patches:
http://lowbyte.de/vga-sync-fields/

New version:
http://www.vdr-portal.de/board/thread.php?threadid=80567

Those might help.. they're about getting pure 1:1 interlaced (576i) RGB output
from a VGA card.. and the new version also has some HDTV stuff, I guess. I
don't read german so i'm not familiar with that..

There are also patches to maintain perfect field sync to DVB stream to avoid
tearing/stutter/jerkiness.

-- Pasi



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