[INFO] Need - Avisynth FPS

[Selur]

15.0 fps up to 30.0

If the content is interlaced, use QTGMC in BOB mode.
If the content is progressive, use the filter under Filtering->Vapoursynth/Avisynth->Frame->Interpolation that best suits your content. (check Vapoursynth/Avisynth preview)

30.312 fps down to 30.000

Try, dropping time codes, usually such small differences come frame a broken time code. (Config->Internals->Handling->Ignore all input time codes)
Or, if it's just a bug in the container frame rate, tell Hybrid to use the stream frame rate (Config->Internals->Prefer Original->Frame rate)
If you really need to drop frames, use the filters under Filtering->Vapoursynth/Avisynth->Frame->Reduction.

23.9 or 29.9 up to 30.0 or up to 50.0

If the content is interlaced, first use QTGMC bob and then 'Frame->Reduction'.
If the content is telecined, first use TIVTC and then 'Frame->Interpolation'.
Depending on the content, sometimes use a combination of 'Frame->Interpolation'- and 'Frame->Reduction'-filters.

Blindly dropping frames or adding duplicates, usually is the wrong approach. You need to understand what type of content you have (progessive, telecine, interlaced, mixed) and what content you want to create and then use the best combination of tools.

Cu Selur