Changing FPS in Vapoursynth

[leonsk]

I'm trying to change framerate without changing the length, but I see only AssumeFPS() is available in Vapoursynth so I decided to do that within the source filter (LSMASH in this case).
But I get bizarre results. The duration is changed to something extremely longer with a slight change, like changing 30 FPS to 29.970, which doesn't make sense. And in the preview tab of vseditor after the original length it shows just blank frames.

Is LSMASH incapable of framerate conversion in VS or am I doing something wrong?

Are there any other ways to convert framerate in VS?

[poisondeathray]

havsfunc has changefps ; this adds duplicates or delete frames to achieve the desired fps but keeps the duration

or you can use motion interpolation to synthesize or retime a new fps, but often there are artifacts

[leonsk]

Wasn't aware that havsfunc had that function. Thank you so much, this does exactly what I want.
Just out of curiosity, do you know the cause of LSMASH's odd behaviour in VS? Does it perform the same in your case?

[poisondeathray]

Not sure about lsmash and changing the FPS ; I've never used it for that purpose

In theory, specifying fpsnum, fpsden should do the same thing as changefps . It works ok on a few clips, but more like assumefps when I did a 24.0 => 23.976 conversion, but 30.0=>29.97 does the same thing as you described

But ffms2 fpsnum, fpsden worked correctly on that 30.0=>29.97 for me

[leonsk]

Thanks for the confirmation. I'll try ffms2 as well.
Gonna report this in the LSMASH thread over at doom9 later, see what the maintainer's opinion is.