[mythtv-users] Big fat blue bar with Internal player

Michael T. Dean mtdean at thirdcontact.com
Wed Jun 22 22:03:07 UTC 2005

Marshall Crocker wrote:

> Oskar Lissheim-Boethius wrote:
>> Switched from mplayer to Internal as the video-player of choice in  
>> KnoppMyth, and now I get a fat blue bar on the top every time I play  
>> a wide-screen movie. I use nvtv for overscan (since I use a shitty  
>> Geforce2MX S-video) but before I did I still got a thin blue line to  
>> the left and top of the movie. On 4:3-movies it doesn't show up.
>> The command I use is simply "Internal".
> I think this is a problem with the nvidia driver.  The default color 
> for the video overlay is blue so it outputs blue for resolutions that 
> do not take up the whole screen.  You have to use the xvattr command 
> to set the overlay color to black:
> xvattr -a XV_COLORKEY -v 0
> You may have to install xvattr.

I'm not sure I'd call it a problem with the NVIDIA driver.  Usually, 
when a driver causes hardware to do exactly what the software requests, 
that's not considered a problem.  ;)

Xv--the X Windows Video Extension--is built around the idea that a video 
area is defined by using a specific color, the color key.  Any pixels on 
screen that were painted that color are replaced with the appropriate 
colors for the video being played.  This allows Xv to use the hardware 
to do a "color replacement" (think green-screens as used in movie 
making) which is much faster than having to determine the appropriate 
boundaries for the video using valid/invalid flags, clipping, etc.

So, why is the default color key an unusal and very unappealing 
blue-green color that's never used anywhere?  Well, exactly /because/ 
it's an unusual, unappealing color that's never used anywhere.  If you 
set the color key to 0 (black) as shown above and put an xterm terminal 
window with black foreground on top of the video while it's playing, you 
might notice the video appearing in the black "behind the words" (or at 
least within the cursor and scrollbars--antialiased text may prevent it 
from showing through the words).  Or, start a terminal with "xterm -bg 
black -fg white" and you can hack your Myth code right on top of TV (a 
true "lightweight" transparent window--all handled in hardware unlike 
aterm/eterm/etc.).  By using a color that's not ever used, this 
"accidental" replacement never occurs.  The valid range of values for 
the colorkey is 0 through 2147483615, so my recommendation is to pick 
something close to--but not equal to--0, such as 10 or 30 or even 1 (all 
of which are only likely to be used for the occasional pixel in 
antialiased text).

Since MythTV is likely to be used such that there are never windows on 
top of the video, using a color key of 0 is not a problem, but on your 
desktop it's likely to cause some unusal (disconcerting?/strangely 
appealing?) effects you might not expect.  And, since human eyes can't 
distinguish between 0 and 10, you might as well choose something 
appropriate that won't be a problem anywhere.

Just wanted to ensure blame doesn't go misplaced.  I'll admit NVIDIA has 
some work to do on their drivers--but not here.  :)


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