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I'm trying to do a smooth zoom in to the center of a 4k video over the duration of that video, so basically zooming in 2.13x so that the zoom in stops when the zoom is equivalent to an HD file (4096 / 1920 = 2.13).

I'm having trouble finding out how I can control the length of the zoom in effect dynamically, for different video lengths.

Here's the command I have so far:

ffmpeg -i "{filepath}" -vf "scale=w=(4096*4):h=(2160*4), zoompan=z='min(pzoom+0.00213,2.13)':d=1:x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':s=1920x1080" "{output1}"

I'm guessing I need to do a calculation on the # of input frames and adjust the pzoom ratio accordingly, but I'm unsure how the pzoom ratio actually works.

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pzoom is the calculated zoom value for the previous frame. It is initialized to 1 at the start of filtering. So, if total no. of frames is X, your zoom expr should be

z='min(pzoom+(2.13-1)/X,2.13)'
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  • Great, I think I get it now. What's the 1.5 value after the comma? I thought it was the maximum zoom ratio, but I see you're keeping it to 1.5 instead of 2.13.
    – JPAllard
    Feb 27, 2020 at 18:03
  • Typo. I forgot to correct that when I copied the original expr.
    – Gyan
    Feb 27, 2020 at 20:06
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    @JPAllard — “Great” in your comment is a nice word — what about enhancing it by accepting and upvoting this answer? (Click on the check mark and on the “up” triangle.)
    – MarianD
    Feb 28, 2020 at 2:16

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