I have a film that used green screen. I'm trying to have the background jpeg track the foreground shot, which moves around much and is quite shaky.

I get the keyframes all set so it looks like the background is tracking the foreground, but when I test run the film it doesn't work. When I drag the pointer they seem matched, when I jump from keyframe to keyframe they seemed matched, but when I run the film it is like the key frames don't exist.

Is it because I'm trying to do movements that are too small? Am I asking too much out of the motion function?

Are you rendering the preview first? or exporting a movie?

Otherwise, it sounds like your computer may just be having trouble jiggling the jpeg (hey, that's not bad! ;-p ) in real time.

andy

PS Aftereffects has a built-in function for this (well, kinda like this) and can give you sub-pixel movements to better match the moving shot.

I'd love to help you out, if you need an effects collaborator. I'm still an amature, but that means I'm extra-cheapaffordable!!

I've done this for some concept footage using shake:

http://www.youtube.com/watch?v=eSiFmEDl_gY

Are you using the new version of Motion for this? I know www.izzyvideo.com has a tutorial about using the new tracker stuff in there.

Izzyt is talking about Final Cut. So far I haven't find motion analyzer on premiere.

You really need After Effects for something like this...

Have a look at Andrew Kramer's tutorial on Sky replacement..http://www.creativecow.net/articles/kramer_andrew/sky_replacement/sky.html

Izzyt is talking about Final Cut. So far I haven't find motion analyzer on premiere.

He's actually using "Motion" part of the final cut suite...

http://www.izzyvideo.com/2007/07/07/izzy-video-57-analyze-motion-and-match-move-in-apples-motion/

although it's a different program with a different interface than AE or Shake or Combustion, the techniques translate...just the workflows and interfaces change.

I'm going to try to get by without buying more software. It's a friend's project, string budget, guerilla filmaking.

I could make the shaking and shifting problem bearable by moving the background jpg constantly. But I'm finding that in certain clips, when I move the time line by dragging the CTI, the clip plays differently than when I play it. Also as a repeatedly go over certain clips, what is played in the AVI file track changes - sometimes it moves faster, or slower, or a section towards the end doesn't get played.

The end result, no matter how I move the background around it doesn't match the AVI clip ( some of them) because the AVI changes. Why is this and how can i prevent this?

If AE isn't in the budget, try using the included plugin called "steady move" (or motion i believe) on the foreground object...
That would be my last step...

I'm going to try to get by without buying more software. It's a friend's project, string budget, guerilla filmaking.

I could make the shaking and shifting problem bearable by moving the background jpg constantly. But I'm finding that in certain clips, when I move the time line by dragging the CTI, the clip plays differently than when I play it. Also as a repeatedly go over certain clips, what is played in the AVI file track changes - sometimes it moves faster, or slower, or a section towards the end doesn't get played...

Export the movie, and evaluate that result. The timeline preview does its best to provide real-time rendering, but it really sounds like the problem is virtual: your computer is not rendering the frame movement quickly enough to give a real-time preview. If you frame-by-frame advance through the preview and everything looks fine, then you may not actually have a problem in the finished product.

I'm going to try to get by without buying more software. It's a friend's project, string budget, guerilla filmaking.

I could make the shaking and shifting problem bearable..

If it's a "problem" you need an un-shaker (I run AE, have done some fixing of this sort, and again, would love to help out.) If the shaky look is desired (that is: it's supposed to look like a hand-held shot), but your match-moves are not working I can help with that too.