You are right. I always wish for more specifics too when we talk about code here.
The library was https://mediabunny.dev/
Before I used my own proprietary code for media encoding/decoding. I also tested a WASM port of ffmpeg for a while.
Mediabunny's documentation might be fine for some developers, but personally I prefer a reference where I have a list of all functions and their specifications.
Yes, I understand the library much better now.