sync xv buffer swap to frame iso field?

I've been running MythTV frontend on my xbox for a while, and managed to
get smooth playback. Nevertheless, I run into a problem related to swapping 
the buffers using xvideo. I hope somebody can help me out. Let me try to 
explain how far I got, and where I got stuck. 

I've put the vertical scaler of the Conexant video-out to match the frame
buffer (4096), and disabled the flicker filter. I get perfect playback for
progressive content. MythTV uses double buffering.

I have a problem playing back interlaced content. I render these interlaced
frames such that the even lines contain the first field, and the odd lines
contain the second field. This works perfectly when the frame buffer 
is refreshed on an even field of the video out. The output becomes
unwatchable/jumpy if the frame buffer is refreshed on an odd field.

I noticed that the current nv driver (4.2) reports 50 fps (I'm in PAL
land). Could anybody give me a hint how to convince the nv driver to
swap buffers on the correct field?

I've been looking into the current xfree cvs, and noticed that the nv
driver has gone through a fair amount of changes (beyond Chris
Bainbridge's patches, that is). Moreover, there seems to be support for
a sync to vblank. I haven't been able to get the cvs version to 
work on the xbox, yet. However, I'm afraid that it will not solve this
problem. Anybody out there, who has a clue?

Any help/input would be greatly appreciated,



Robert-Paul


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