Optical flow versus Frame blending

It depends entirelty on the content. Flowing water might not make much difference. It helps most on a panning shot, where the camera is panning with something and the background is moving.

As far as I understand these - for me new - techniques, blending means the whole two frames are dissolved into each other. in result a smooth movement reception, but blurry.

optical flow analyzes the content, differs between static and moving elements plus movement's direction. depending on the quality of algorithms, results could be superb (probably you've seen the demos of TWIXTOR, an OF plug-in for FinalCut/pro)

as a hobbyist doing sport-movies, slow-mo is essentiell.

here's a test:

http://youtu.be/xG0p4XxsR3s

recorded with 60p, and a high shutter speed. project's fps iss 25fps.

'natural motion blurr' (=slow shutter speed) irritates OF.

for OF mode best result with short shutter.

for blend mode, better result with slow shutter (naturally blurred frames)

the distant players 'flow' very nice.

close up action (=high angular velocity) starts to ... wobble.

and in the last segment of my demo, you'll notice the rotating ball confuses OF too ... its surrounding gets liquid .

but these are in theory 600fps - calculated from 60 ... I shouldn't expect wonders 😁

If you're slowing down to 25% you're better using Optical Flow.

With Frame Blending (as Karsten Schlüter said) you get a dissolve of two frames to make a third one (in between them). This works quite well down to 50% where every other frame is a dissolve of two originals - but when you get more than one 'manufactured' frame between two originals, it gets a bit 'hit-and-miss' and things can go out of shape.

Optical flow tends to make a better job in these extremes.

Andy