The majority of code in ffmpeg today isn't written by Fabrice, but also there's multiple axes that people view programming ability on. Some people can write software that will do things you couldn't imagine given the constraints. Some people can write software that is resilient against all malformed input. Sometimes these people are the same people, but frequently they're not.
Can't help laughing at a random ad hominem against John Carmack of all people, and about his opinion on a guy who is already widely regarded as an especially talented programmer.
I don't think that's fair. There's a lot of talent and grit behind ffmpeg. But for better or worse, getting the code to do what it's supposed to do requires a different mindset than getting it to not do anything else (i.e., to handle malicious inputs correctly).
The developers of ffmpeg are very good at the first thing and not very good at the second. But few people on this planet, if instructed to write a complex video format parser in C or assembly, can produce something that's secure on the first try. The main failing of the ffmpeg team is that they should have spent more time on architectural hardening and mitigations. Most other large projects of this type do.
My understanding is that ffmpeg is probably incredibly close to the metal, with tons of assembler mixed in. I imagine doing the same in Rust would include lots of `unsafe` blocks and a similar amount of assembly, so it wouldn't change much in terms of security. Or am I wrong?