For those of you that have used Time Remap filter, you may know that it can be difficult to smoothly increase the speed of a video. You could use Smooth keyframes, but my understanding is these operate similar to a sine function: they build slowly initially, have the highest rate of change in the middle of the two keyframes, then gradually slow to the next keyframe, making for usually better motions that don’t feel robotic or jarring as opposed to linear motions. But when Smooth keyframes are paired with Time Remap, you tend to get a video which starts slow, speeds up, then slows down again between each keyframe.
If instead you’re looking to gradually increase video speed and audio pitch (e.g. go from 1.0x video speed to 2.0x video speed with a parabolic function) about the only way to do it is with Linear keyframes. However the change between one speed and another is so sudden, you get a very jarring transition from say 1.0x speed to 1.1x or 1.2x, etc. This “jarring” feeling tends to be the audio suddenly changing pitch, while the change in visual video speed is usually less noticeable. You could theoretically make it look much smoother with many, many, many linear keyframes with small speed increments, but this would be extremely time consuming.
The solution I figured out (which seems kind of obvious in hindsight) is instead to enable Pitch Compensation on the Time Remap filter and make your video speed increase with linear keyframes as you would normally. After you’ve got that figured out, add a Pitch filter and use that to smoothly increase the pitch of the audio with keyframes. Added benefit: the pitch doesn’t necessarily have to perfectly match the speed increase, it just gives the illusion that both are increasing smoothly together.
Video attached shows the difference. Hope this helps and let me know if you found another solution or if any of this could be phrased better to improve understanding!
Note: you can of course add more keyframes to Pitch to make it match better but it is entirely up to your discretion. The point is that those linear changes in a Pitch filter tend to sound much smoother than linear changes in Time Remap. Also the video clip I’m using was just the first example I took from a video I’m making, so it may not show “jarring” effects with visual changes in video speed as well as a different video clip might.