Here's a comment to Emacs: ffmpeg and macOS aliasing commands on Hacker News.
I use Typinator expansions with the input video path (from the clipboard) as a variable to perform common ffmpeg operations, such as downsize, speed up, extract audio, strip audio, export frames to create GIF animations, or encoding as MP4. Typinator lets you use what's on the clipboard but also add scripting (say, Python or JavaScript) when certain parameters need to be calculated, like sizes or names.