Old anime : How to replace duplicate frame

[Atillart]

Hi, I have an old animated film that I'm cleaning up and stabilizing to give it a more modern look.

As is often the case with animation, it's mostly animated in 12fps and sometimes 8fps.
I'd like to replace similar frames with others so they're 100% identical. Because of their analog nature (film), they have slight variations.

Do you have any tips for detecting all the "similar frames" and replacing them with a single one please ?

[Selur]

First thing you should do is clean your source to remove noise&co.
Then, if you want to do this manually, something like https://www.vapoursynth.com/doc/functions/video/freezeframes.html or ReplaceFramesSimple could be used.
One could also write a small script to replace frames that only differ less than x with the previous frame.
=> should be easily doable with Avisynth or Vapoursynth
I even wrote a Vapoursynth function for this a while ago:

def addDup(clip: vs.VideoNode, thresh: float = 0.3, debug: bool = False) -> vs.VideoNode:
    """
    Detects frames with low temporal difference compared to their predecessor and duplicates the previous frame
    if the difference is below the given threshold. Optionally adds debug metadata.

    Parameters:
        clip (vs.VideoNode): Input video clip.
        thresh (float): PlaneStatsDiff threshold for duplication.
        debug (bool): If True, adds debug props to output frames.

    Returns:
        vs.VideoNode: Modified clip with duplicates inserted when differences are below threshold.
    """
...

(see: addDup)
The function is small and documented, so understanding the idea behind it should be easy.

Cu Selur

[ajk]

There is also an AviSynth plugin for this purpose: http://avisynth.nl/index.php/Dup

[Selur]

Ah, totally forgot about that.

[Hunk91]

You can also try Filldrops which will replace a duplicate by an interpolate frame. But the frame must be tagged as Duplicate.

Filldrops.avsi

function filldrops (clip c)
{
vf=c.mvanalyse(truemotion=true,pel=2,isb=false,delta=1,idx=1)
vb=c.mvanalyse(truemotion=true,pel=2,isb=true,delta=1,idx=1)
global filldrops_d = c.mvflowinter(vb,vf,time=50,idx=1)
global filldrops_c = c
c.scriptclip("""ydifferencefromprevious()==0? filldrops_d : filldrops_c""")

}