Embedding scripting language in a filter element

[Josh Doe]

I've often had a need to apply some simple processing to a video,
little one-off things that don't seem worth creating an element for.
I've either done quick hacks to an existing element or the
application, but I'd like to have a better way. I think it would be
useful to have a filter element that has a script property, some
interpreted language like Python or Julia, to allow even interactively
changing the script. Has anyone done this or something like it? The
closest I can find is glshader for running OpenGL fragment shaders.

Thanks,
-Josh