I am playing back footage 250% faster than it was originally shot at, but I want it to end at 100% by the time the clip ends playing. How can I gradually drop the speed from 250% to 100% so that it does not come off as jarring to the viewer?
The answer, in a word: keyframing.
Mark is right, of course, but he didn't tell you what to keyframe.
Use the Time Remapping effect.
There are tutorials available for this effect. This one is for CS5.5 but it applies to newer releases as well.
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