what the difference between assume fps and change fps in AviSynth

[gavo]

what the difference between assume fps and change fps in AviSynth ?

[Manao]

Taken from the documentation : The AssumeFPS filter changes the frame rate without changing the frame count
ChangeFPS changes the frame rate by deleting or duplicating frames.

[gavo]

Why would u want to duiplicate or delte frames when u can just assume them? what the point of useing the chargefps?

[Manao]

Well, mainly, AssumeFPS will speed / slow down the video, while ChangeFPS will let the length unchanged and decimate / add frame in order to respect the framerate you asked.

[stickboy]

To provide an example: let's say you have a video that's 10 minutes long and is 30 fps.

If you use AssumeFPS(15), no frames are removed, so the framecount remains the same, and you've slowed down the video to be 20 minutes long. Note that you've only changed the video track, so the audio is still 10 minutes long and now is out of sync.

If you use ChangeFPS(15), frames will be deleted as necessary to retain the original video duration.

[gavo]

thanx for the expection.