Originally Posted by Steve T
that's another way of saying interpolation. You should get a much better, more accurate, result going from 60 down to 30 than 25 up to 30, either way is mixing frames.
Interpolation can mean many things. Modern standards conversions usually do actual motion interpolation, where entirely new frames are created based on motion vectors, not by blending together two existing ones. Motion interpolation can also be used to simulate motion blur. But YouTube does not do that, and it's anyway usually not that great for "unnatural" material like our games or demos.
Going from 60fps to 30fps (or 50 to 25) with frame blending just means that you have a 50/50 mix of two frames each time. I usually just drop 50fps to 25fps by simply leaving out the other frames - motion is not as smooth but frames are left perfectly clear.
Some games present a problem when doing this, however, since they use a 50Hz flicker to simulate transparency or other effects (eg. Turrican, Superfog and many others). If you just drop frames here, the effect is lost (either you get a missing player character or no transparency/flicker at all). When uploading such material, I have used a custom blending filter, which attempts to retain the effect where it exists without blending entire frames.
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, Turrican 2 and Lionheart are processed like that, others are just decimated to 25fps.
Unfortunately Vimeo doesn't keep anything above 30fps either, it will get converted.