Ok, so using the overlay filter, one can change the x/y location of a video over time by using the "t" variable. For example, overlay=x='if(gte(t,2), -w+(t-2)*20, NAN)':y=0 can be used to start sliding an overlayed element from the top left to top right, after 2 seconds has passed.

What I want to do is to use a similar principle for scaling elements. I would like to be able to change the scale of a video over time by using an expression (like, scale=w=iw*t, or something along that line).

Is this possible?

when I run that expression through -filter_complex, I get

Error when evaluating the expression 'iw*t'.

Maybe the expression for out_w:'iw*t' or for out_h:'-1' is self-referencing.

I'm feeling like there's a fair chance I'm going to need to patch FFMpeg if I want to get this functionality, but I thought I would ask first, to see if anyone would be in the know about this kind of thing!

Does anyone know how such a task might be accomplished?

Thanks for the help!

  • Sounds more like a syntax error right now but I haven't used that feature before so unfortunately I can't really help here.
    – timonsku
    Jul 10, 2014 at 19:51
  • 1
    t is not a defined thing when it comes to overlay filter.
    – v010dya
    Jul 17, 2014 at 16:01
  • 1
    You could just write a filter. wiki.multimedia.cx/index.php?title=FFmpeg_filter_howto
    – denjello
    Aug 7, 2014 at 12:50
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    @alexspeller the scale filter does not support timeline editing, so not directly possible. I'll check if there's a workaround.
    – Gyan
    Feb 1, 2017 at 5:34
  • 1
    Technically possible with H.264/5 output. Don't know how players/editors will handle it.
    – Gyan
    Feb 1, 2017 at 9:25

1 Answer 1


From what I understand 't' is evaluated once. Have you read this: https://ffmpeg.org/ffmpeg-filters.html#zoompan ?

Ffmpeg Docs:

9.170.1 Examples

  • Zoom-in up to 1.5 and pan at same time to some spot near center of picture:


  • Zoom-in up to 1.5 and pan always at center of picture:


  • Same as above but without pausing:


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