I have a background image that I'm trying to fade to specific color values using this filter: lutrgb=enable='gte(t,3)':'r=0.3*val:g=0.3*val:b=0.3*val'

This almost works, but it changes the values instantly. How do I get it to fade to those values gradually over time?

  • Your example doesn't alter alpha but the color channels. Is that what you want?
    – Gyan
    Apr 14, 2017 at 15:48
  • Sorry, I was messing with alpha earlier and the word "opacity" stuck. I'm simply trying to get the background image to partially fade/darken, not become transparent.
    – HDL
    Apr 14, 2017 at 16:01

1 Answer 1


The lut filter expressions don't work with time. geq does.

geq=r='(1-0.7*min((T-S)/D,1))*p(X,Y)':g={the same as r}:b={the same}:enable='gte(t,S)'

S should be your start time in second. D is duration for the change in colours. T and p(X,Y) are variables and should be kept as is.

  • Gives me an error. I tried both substituting each S with the start time and not substituting. [Parsed_geq_0 @ 0x7fa6ab5007c0] [Eval @ 0x7fff576460e0] Unknown function in 'S)/D,1))*p(X,Y)' [AVFilterGraph @ 0x7fa6ab413a80] Error initializing filter 'geq' with args 'r=(1-0.7*min((T-S)/D,1))*p(X,Y):g=(1-0.7*min((T-S)/D,1))*p(X,Y):b=(1-0.7*min((T-S)/D,1))*p(X,Y):enable=gte(t,3)'
    – HDL
    Apr 14, 2017 at 16:58
  • S and D have to be substituted with numerical values.
    – Gyan
    Apr 14, 2017 at 17:15
  • I got it working, however it's slowing the rest of the encoding process to a crawl. How do I get it to resume normal encoding speed?
    – HDL
    Apr 14, 2017 at 17:46
  • Change enable to between(t,S,S+D) And add your lut filter for gte(t,S+D)
    – Gyan
    Apr 14, 2017 at 17:50
  • I get an error trying that. Here's what I have: geq=r='(1-0.7*min((T-3)/3,1))*p(X,Y)':g='(1-0.7*min((T-3)/3,1))*p(X,Y)':b='(1-0.7*min((T-3)/3,1))*p(X,Y)':'between(t,3,3+3)',lutrgb=enable='gte(t,3+3)'
    – HDL
    Apr 14, 2017 at 22:45

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