How to get smooth progressive conversion from interlaced vid with Avisynth?

[VideoFanatic]

I've seen some Xvid torrents which are progressive NTSC or PAL yet the frame rate is still 29.97 or 25 fps and the frame rate is smooth. How can this be done with Avisynth as I thought if you convert interlaced to progressive then you'll get a choppy frame rate unless you double the FPS. I don't want to double the FPS because then my video won't be Bluray compliant.

[jagabo]

You can't. A true 30i source (typically live sports, news) converted to 30p won't look too bad but it will flicker during bright high motion sequences and will be noticeably less smooth than converting to 60p. Compare the 30p and 60p rows in the first video (24v30v60.avi) in this post (watch it full screen for greatest effect):

https://forum.videohelp.com/threads/307004-Best-framerate-conversion-%28eg-23-97-to-30-...=1#post1888926

If you blend the two fields together it will flicker a little less but you will get fuzzy or double-exposure frames.

A film source will have several little jerks every second because every 5th frame will be a duplicate. Or if you blend the two fields together you will get an annoying phasing effect during motion because two of every five frames is fuzzy.