[Libva] Strange flickering in first row of pixels when using vaapi

[Timo Rothenpieler]

Hi,

I'v seen this accross several version of libva with intel-driver, and 
I'm not sure where it comes from, but it's very annoying.
Currently i'm using the latest staging libva and intel driver.

First I noticed it in XBMC a while ago, and now i ran into it again, 
while writing a libva-accelerated encoder.

It's basicaly the first half of the top row of pixels which is 
flickering from black/some garbage to the real image.
When watching a video with XBMC, this just is annoying, but when 
encoding it leads to a lot of artifacts.

XBMC uses OpenGL and the vaapi GLX functions to render the image, and my 
Encoder writes the yuv data(which i checked to be correct) in a mapped 
VAImage which was derived using vaDeriveImage.

Does anyone know what might be causing this, and how to fix it?