SlowMo: Simple slow motion, using interpolation

[spoRv]

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### SlowMo 1.01: Simple slow motion, using interpolation                                ###
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### Usage:   SlowMo(clip,multiplier)                                                    ###
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### Example: want to make clip to play at half rate                                     ###
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###          SlowMo(clip,2) - or just SlowMo(clip) as 2 is the default value            ###
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### AviSynth script made by spoRv (http://blog.sporv.com) - Created: 2016-12-05         ###
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### Creative Commons 4,0 - Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)      ###
### Link to the licence page: https://creativecommons.org/licenses/by-sa/4.0/           ###
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function slowmo(clip clip, int "mul") {
num=clip.FrameRateNumerator
den=clip.FrameRateDenominator
mul=default(mul,2)
clip.assumefps(num,den)
backward_vec = clip.MVAnalyse(blksize=16, isb = true, chroma=false, pel=1, searchparam=1, idx=1)
forward_vec = clip.MVAnalyse(blksize=16, isb = false, chroma=false, pel=1, searchparam=1, idx=1)
last.MVFlowFps(backward_vec, forward_vec, num=num*mul,  den=den, mask=0, idx=1)
assumefps(num,den)
}

Needed to slow a shot in a clip, I searched for a proper script, but haven't found it; I thought to use InterFrame, and assumefps at half the final rate, but was too "heavy" for my old PC... I just needed something better than ConvertFPS...

Found a code here: http://www.avsforum.com/forum/26-hom...ame-rates.html - take it, slightly modified - with my limited knowledge - and corrected the most important thing, that nobody seems to take in account: when a film (23.976fps = 24000/1001) must be converted to double frame (for interframe purpose or, like in this case, for a slow motion) it should be 48000/1002 and NOT 48000/1001... with this error, an entire movie will have many frames less, and audio will be audibly out of sync after few minutes. I was wrong, 48000/1001 is the right number; corrected the code to reflect this.

My little contribution; hope this code is right (if not, feel free to correct/improve it) and could be useful for someone.