[mythtv-users] PVR-350 TV-out distorted

Michael T. Dean mtdean at thirdcontact.com
Wed Apr 7 14:06:19 EDT 2004


Thomas Börkel wrote:

> The test picture comes out OK from the PVR-350, but if I play MPEG 
> (either with the dd command directly from /dev/video0 or with MythTV), 
> the output is totally distorted. You can guess, that it's a TV 
> picture, but it's teared in multiple directions. Looks like you feed a 
> monitor with the wrong frequency, but that can't be, because my TV is 
> able to display PAL and NTSC.
>
> I am using ivtv 0.1.9 and I have not yet switched X to the PVR-350.

Sounds like the "teared" picture you're getting is actually a 
semi-transparent view of your framebuffer's "picture" on top of the TV 
picture.  Since you haven't set up X, the framebuffer's "picture" is 
actually garbage (some semi-random initial bits in the framebuffer).  
Most instructions I've seen refer to this as "about 20 colored lines in 
the picture," but for me it was a mess of garbage (sometimes opaque and 
sometimes semi-transparent) obscuring the view of the TV picture.  Note 
that the test picture works because it actually uses the framebuffer 
instead of the TV "underlay."

Basically, try these commands:

# Assuming NTSC via S-Video input
test_ioctl -u 0x3000 -p 6
# This makes the framebuffer image transparent
ivtvfbctl /dev/fb1 -globalalpha -nolocalalpha -alpha 0
dd if=/dev/video0 of=/dev/video16 bs=64k

(Note the slight difference in the ivtvfbctl line from most posts which use:

ivtvfbctl /dev/fb1 -alpha -on -globalalpha -nolocalalpha

Interestingly enough, that command works, also, but only by "accident."  
The -alpha option requires a value for alpha from 0 (transparent) to 255 
(opaque) and uses the first "word" after "-alpha"  That word happens to 
be "-on" (which is supposed to mean "turn on the framebuffer" and is 
never required), but it's not a numeric value "-alpha" expects, so 
"-alpha" goes with its default of 0. )

Then, once you have set up X, you can set the framebuffer's background 
using your normal background changer (i.e. I use chbg ( 
http://chbg.sourceforge.net/ ) because it has very few library 
dependencies).  Once you have a "pretty" picture (instead of garbage), 
use the following to go back to an opaque framebuffer (and see your 
picture):

# This makes the framebuffer image opaque
ivtvfbctl /dev/fb1 -noglobalalpha -nolocalalpha

HTH.

Mike


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