battling judder with Xv video playback

[Torgeir Veimo]

I'm battling with judder in my setup with vdr & Xv output with streams
decoded using libavcodec, and I'd like to try to find the real cause for
this (am suspecting libavcodec). 

Therefore it would be of tremendous help if I was able to instrument the
X server in some way to log the timestamp every time a new frame is send
using Xv, and the timestamp the frame is actually blitted to the hw
scaler. In this way I can find if the problem is in the X server /
scheduler, or if it's a more fundamental problem with the decoding
process itself.

Does anyone have any idea of the best way to approach this? I'm not too
familiar with X server internals and what would be the best way to
implement a log mechanism that wouldn't affect the overall playback
process itself.

-- 
Torgeir Veimo <torgeir at pobox.com>