I wanted to see if I could build a video downloader that didn't rely on a massive backend to do the heavy lifting. I made www.ultimadownloader.xyz and the secret is that it runs yt-dlp via Pyodide and ffmpeg.wasm entirely in the browser. Feel free to poke around and give it a shot. I would love feedback and ideas on what to add later (I plan on adding more sites and such). If you find any issues, please let me know. It's not perfect but its something.

It crashes on the first video i tried:

https://www.youtube.com/watch?v=XO9FKQAxWZc

Relevant part:

> ERROR: [youtube] XO9FKQAxWZc: Sign in to confirm you’re not a bot. Use --cookies-from-browser or --cookies for the authentication. See https://github.com/yt-dlp/yt-dlp/wiki/FAQ#how-do-i-pass-cook... for how to manually pass cookies. Also see https://github.com/yt-dlp/yt-dlp/wiki/Extractors#exporting-y... for tips on effectively exporting YouTube cookies

The app provides no way to pass flags, though (and the browser is confirmed to be logged in to youtube).