Rust currently isn’t as performant as optimized C code, and I highly doubt that even unsafe rust can beat hand optimized assembly — C can’t, anyways.

A bit tangential, but to answer this question, nothing beats the most optimized assembly code. At best, programming languages can only hope to match the most optimized assembly.

Rust does have macros for inlining assembly into your program, but it’s horribly unsafe and not super easy to work with.

Rewriting ffmpeg in Rust is not a solution here (like you’re saying).