[mythtv-users] MythTV on a 4:3 HDTV [PATCH]

John Patrick Poet john at BlueSkyTours.com
Sun Jul 11 19:46:16 EDT 2004


Doug Larrick wrote:

> homebreweverything wrote:
>
>> I have a 4:3 WEGA HDTV-capable set.  Is it possible to use a video 
>> card with 
>
> DVI out, or a VGA->DVI converter or a VGA->component converter to display
> 4:3 content?  The modes I've seen discussed for HDTV converters are all
> 16:9, but I have a lot of 4:3 content that would then get letterboxed to
> 16:9 on the TV, which would be letterboxed to fit 4:3, so there'd be a
> letterbox all around the image I beleieve.
>
> This is in fact a problem for people with 4:3 HDTV sets.  Building on 
> my recent (0.15) work to use a different video mode for playback vs. 
> GUI, it would be easy enough to use different modes for different 
> aspect ratios, different channels, etc.  Then you could use 480p for 
> 4:3 modes, which should use the whole screen.  The difficulty is a GUI 
> to configure all this (and also support DVB, which has its own aspect 
> ratio issues that I simply have never understood).  I myself have very 
> little incentive to work on anything like this, as my set is 16:9, but 
> it's a simple enough task it might be a good way for somebody to get 
> their feet wet.
>
> -Doug


Sorry, I have lost the other emails from this thread, so I don't know 
your name, but...

homebreweverything,

Here is a patch you can try.  I submitted it to the devel list a week 
ago, but it will probably be a while yet before it becomes part of the 
CVS -- It only helps those of us doing HDTV and there are not that many 
of us, so I am sure it is a low priority for Isaac to validate.  I 
believe it still applies cleanly to the current CVS.

It takes a patch by Doug Larrick to the next level.  His patch allowed 
for a separate video display resolution from that used by the GUI.  As 
with Doug's patch, this one places the user options under the main 
Appearances setup menu.

This patch allows for up to two alternate display resolutions to be 
specified, which are triggered by the resolution of the source video.  
For example, my default "display resolution" is 1920x1080, but if a 
720x480 "video resolution" is detected, then the display is switched to 
720x480.

It also allows for the display aspect ratio to be overridden.  This is 
merely a toggle.  If X's DisplaySize indicates an aspect of 4:3, and 
this toggle is enabled, then a display aspect ratio of 16:9 will 
actually be used -- and visa-versa.  This allows proper display of 4:3 
material when the display is switched to a 4:3 mode.

The code itself can actually accommodate an unlimited number of 
"alternate resolutions", but I could not figure out a clean way of 
allowing the user to specify more than two on a single options screen.

Two new files are included in the patch: DisplayRes.cpp & DisplayRes.h.  
These define a class which manages the resolution switching.

I personally rarely watch live TV, however, when watching live TV with 
this patch, the display resolution can end up changing between every 
channel.  I originally had it coded just to make a system call to 
xrandr, but that added a noticeable delay.  I re-coded it to use the 
xrandr library, which improved the performance.  Since it now uses 
library calls, I have protected the code with a config option in 
settings.pro.  I don't know how many people are using an old version of 
X which does not include xrandr.  Those using Macs or Microsoft boxes 
probably cannot use it either.

I have tested it with Xv and XvMC.

John



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