I’ve built a pretty functional web-based video editor that helps you generate FFmpeg commands in a visual, node-based environment. The tool lets you play around with most (but not all) FFmpeg filters, render videos in the browser (!), import your own files and/or work with demo videos, export gifs and mp4s, and it comes with a few built-in examples of the many fun things one can do with FFmpeg.
Source: https://lav.io/notes/ffmpeg-explorer/
Code: https://github.com/antiboredom/ffmpeg-explorer