I am having trouble visualizing what you are looking to do. Lets say that you have a ball boucing across the screen over the coarse of 500 frames. You want to shorten the clip to 100 frames. In my experience in animation you either need to get the ball to bounce faster across the screen to effect the time difference or the ball can keep the same rate of motion but only get 1/5th of the way across. Remember that movement is an algebra equation.
Speed x Distance = Rate
Which variable in this equation are you looking to modify? If you want the ball to stop at somme point in the middle of its travel from one side to the other than you are adjusting the distance. If you want the ball to get to the other side faster you are adjusting the speed. Both are extremely possible on this timeline, just let me know what you are interested in changing and I can be of more help.
Also, I have had program glitches in both Mac and PC when using Motion Tweening with Flash CS2,CS3, & CS4. Most of these glitches are resolved by restarting the program or the computer but you can also just remove the tween, make your adjustment, and reapply the tween once you have shortened the timeline.
Thanks for the response Just_BE.
While extending & decreasing a layer + it's Motion Tween is a great feature, I simply want to cut a layer with 500 frames which happens to have a Motion Tween where the action is happening in the first 80 frames, without removing the Motion Tween first. It's very odd & limiting that you can't simply cut frames from a layer when a Motion Tween is enabled on that layer.
Essentially this means when creating a Motion Tween on a layer, you must know in advance exactly how many frames you want the tween to be. Otherwise you're limited to editing the length while simultaneously editing the tween duration. That is ridiculous. You should be able to setup a layer with 100 frames, tween the position in the first 40 frames, and then if that suits you as a proper length, cut the remaining frames. The Adobe Flash team needs to look at After Effects for effective timeline tweening & editing.
If your using CS5... this is how you do it.
On a PC-
Control click on the frame you want the tween to end.... frame 100
From the drop down select "Split Motion". This will inset a key frame.
Next... hit delete... that will delete all the frames from 101 and beyond.
To clean it up... right mouse button click and select" Remove Tween".
I hope this helps.
Thanks Jason Jam! That does it.
On a Mac it's the Command key, and hitting delete or backspace does not remove the split keyframe, but you can right-click the split key and select remove or clear keyframes. Thanks so much.
Would be great if the After Effects team redeveloped the Flash timeline editor. It's like night & day.