ffmpeg source repo updates, custom builds

[trevorgithub]

Hello,

Thank you for your work in bringing ffmpeg to the web. I've just started looking at the project, and I have a few questions I hope someone can help me understand.

It appears that @ffmpeg/core is the transpiled output from C code. And I think that comes from here, if I understand correctly:
https://github.com/ffmpegwasm/ffmpeg.wasm/tree/main/src/fftools

The files above in turn appear to be a fork of the files from here:
https://git.ffmpeg.org/gitweb/ffmpeg.git

Q1: Do I understand this correctly?

Q2: Since the files appear similar, how do updates from the source repo get applied (or maybe they don't)?

I also understand that it's possible to create custom builds of ffmpeg.wasm, as per the docs here:
https://ffmpegwasm.netlify.app/docs/faq#how-can-i-build-my-own-ffmpegwasm

Q3: When building custom builds of ffmpeg.wasm, is it turning on or features of ffmpeg, that is from the source forked above?

Thanks for your help!
Trevor

[trevorgithub]

There's a similar project, libav.js, which uses quilt patches as an alternative to doing a full fork. Might be an interesting thought for this project too, if you don't have a better idea. @jeromewu