IVTC on recorded tv - tdecimate() getting hung up on channel logo overlay

[FrankWDoom]

I'm transferring some tv episodes from vhs tape. The show source is pretty obviously 24p. The recording was made from an sd channel years ago so it's captured as 30i. There is a network logo/overlay text that is generally static and not an issue, but is occasionally animated (probably in 30i).

I'm using avisynth and tfm/tdecimate. This generally works well, except when the overlay logo animates over the duplicated show source frame. tdecimate sees the change in the overlay and keeps both duplicated frames, and discards another frame it should be keeping.

I have attached a gif showing the behavior. you can see the video kind of catch when the animation happens and a source frame is repeated, and the debug info tags a different frame in sequence as the duplicate.

for my script I'm using

tfm(y0=360,y1=460) # setting the exclusion band range (720x480 originally)
tdecimate( display=true , hint=true, denoise=false) # denoise does not help

I was hoping the exclusion band from tfm would carry over but it seems it doesn't.

What's the best way to deal with this? Is there a way to tell tdecimate() to ignore that area of the picture? Some other approach? I think if all else fails I will try using remapframes() and swap the 2nd frame in the animation with the first, it'll get identified properly, but that's kind of tedious.

[poisondeathray]

Is there a way to tell tdecimate() to ignore that area of the picture?

tdecimate has a clip2 parameter that it can take frames from and returns

metrics are done on the input clip (eg. you can crop to an area of interest), but clip2 "full frames" are returned

[FrankWDoom]

awesome thanks. that seems to take care of my issue. here's my revised script

vp = tfm(v, y0=360,y1=460) # v is 30i video, output 30p
vc = crop(vp, 0,0,0,-120) # cropped below line 360 to exclude overlays
vc.tdecimate( clip2=vp, display=true , hint=true, denoise=false) # evaluate cropped 30p video for decimate, return frames from 30p stream