What the "--var" stand for?

[I12learn]

Hello,

back to some programming I'm interested to resize some video, so that DLNA clients won't complain.For GUI I found this script, but my liking would go for MP4 container and for linux porting. I would be able to make it platform independent.

The batch processing should read the directories and keeping the same aspect ratio to decrease those videos that don't pass smartphone characteristics.
My attempt would use avidemux(2|3)_cli and I wonder how it would be the --var usage.
I think it should pass in the variable to the --run script, so I'd think to pass new height and width in that way.
Important is that I won't expect to use a GUI, therefore this would be a good mode and let python calculate the new dimensions.
One more thing, how do I ask height and width to avidemux?_cli?