I basically have an even simpler version of something like this for my own personal use too. I found it pretty easy to write in Go and my area of expertise is decidedly not web frontend/backend. I’d recommend it as a fun little project if you’re looking for something to do.

For mine, I paste in a video or playlist URL and it downloads the video and creates a lower resolution transcoded version suitable for streaming to my phone. It also extracts an audio-only version in case that’s more appropriate.