Thanks again, think you nailed it.
eg, if you have a BD at 23.976 and your TV on 50 or 60hz you will see judder from a Pull Down pattern that is especially noticeable on panning shots etc.
Checked the internet and it seems to be a well known and common problem, never heard of it before.
When I put the refresh rate on either 23 or 24Hz (in the display settings directly) the movie runs smooth. With 50, 59 or 60Hz it stutters/judder. But changing this just to watch a blu ray is kind of a hassle. Not sure if it is a problem to leave it on this setting permanently. It does prove however the cause of the problem.
Before this I started with changing the display settings in JRiver, but whatever I set it to the results were the same (judder) so it does not seem to take any affect. I have put Film(23.976 fps) on 1920x1080x32x23/24/50/59 and even did this for all other options (Film(24 fps), NTSC etc) but nothing happens. Display settings is enabled and videoclock is selected.
But I was wandering, the blu ray is played back via an external program (powerdvd10), so I can imagine that powerdvd is in control and the jriver settings are ignored. This would mean the problem lies with powerdvd. unfortunately In powerdvd it is not possible to change refresh rate.
Well I hope you can shed some more light on this.
ron