For awhile now, we've been able to change the speed of a clip by context clicking on a clip in the timeline and selecting Speed/Duration or the rate stretch tool. These tools do have a limitation though, they are permanent. They cannot be animated or changed over time.

Premiere Pro CS3 introduces the ability to change speed over time, hence, the tutorial on time remapping:)

1. You'll notice that once you select a clip, in the Effects Control Panel there will be a time remapping option present along with Motion and Opacity. To get to the Tim Remapping option, just select it from the top of the clip itself. It will be set to Opacity by default until you change it. Select Time Remapping>Speed

2. This yellow horizontal line is what is used to control the variation in speed. By clicking and dragging up, you'll notice the number increases. If I release the mouse at the point in the screenshot below, the clip would play at 157% of its normal speed. It will also shorten because I've increased the speed at which it's going to play back. If I dragged the horizontal line downward then it would have the inverse effect and make the clip longer, but much slower. Note: You cannot speed the clip up any more than 1000%.

3. Select the point at which you want the speed to slow down and Ctrl Click on the yellow rubberband (horizontal line) to add a keyframe there. We can set it to vary now at that point in time.

4. Be sure to notice how Time Remapping keyframes look because they are different from standard keyframes. Unlike standard keyframes, time remapping keyframes can be essentially split in half.

5. By dragging the one of the right and moving it to right, a gap will be created. This gap is the transition between the speed changes. For a smoother transition, these need to be farther apart and more an abrupt transition, they will need to be closer.

6. By Ctrl Clicking on the half of the keyframe and dragging, it will reverse the clip.

7. Also, the programming going on behind the scenes to get this to work properly is pretty intense. To ensure that everything will work properly you will want to go to Clip>Video Options> and make sure that Frame Blend is checked. This will ensure that you have the highest possible stretch when you're slowing down your video.

By far, Time Remapping in one of  Premiere CS3's most impressive new features!