ffmpeg overlay x expression with logical condition

Question

I am trying to create a simple overlay graphic where the overlay moves and screen and changes speed according to time. So I tried a simple

ffmpeg -i input.mp4 -vcodec qtrle -i overlay.mov -filter_complex '[0:0][1:0]overlay=x=if(t<2\,t*3\,t*5)[out]' -map '[out]' -y output.mp4

and got an error code of :

[Parsed_overlay_0 @ 0000003f4e1e2ea0] [Eval @ 0000003f4c0fe5b0] Missing ')' or too many args in 'if(t<2,t*3,t*5)'

[Parsed_overlay_0 @ 0000003f4e1e2ea0] Error when evaluating the expression 'if(t<2,t*3,t*5)' for x

[Parsed_overlay_0 @ 0000003f4e1e2ea0] Failed to configure input pad on Parsed_overlay_0

Error configuring complex filters.

Invalid argument

if I remove the "if" part and just leave a formula it works :

-filter_complex '[0:0][1:0]overlay=x=12+t*3[out]'

I tried playing with escaping of the different characters but it doesn't look like its a parsing error. Any ideas of how to use this correctly? The ffmpeg documentation has a sample for doing font color expression with a logical value here , but any attempt at

overlay=x_expr

doesn't really work as well

please help

Thanks in advance

Answer 1

FFmpeg uses functions, rather than operators, for conditional execution and comparisons, so t<2 is not a valid syntax.

The syntax for your given command would be

ffmpeg -i input.mp4 -i overlay.mov -filter_complex \
       "[0][1]overlay=x=if(lt(t\,2)\,t*3\,t*5)[out]" \
       -map '[out]' -c:v qtrle -y output.mp4

where lt(var,value) is the less than function.

Answer 2

Here's an example of how to crop landscape videos to square (1:1 aspect), while not cropping portrait videos:

-filter_complex "[0:v]crop='if(lt(in_h,in_w),in_h,in_w):in_h'[out]"