Cryptography and video codecs are notable exceptions, they put a lot of effort to making the code provably memory safe: no recursion, limited use of stack variables, no dynamic allocations, etc. As a result, memory safe languages bring nothing but trouble by making it non deterministic, that’s especially true for crypto where compiler “optimisations” guarantee you side channels attacks.

For the codec itself, the majority of it is performance sensitive and often has a significant amount of assembly even, so a memory safe language doesn't change much.

However for the container/extractor... those should absolutely be in a memory safe language, and those are were a lot of the exploits/crashes are, too, as metadata is more fuzzy.

As a practical example of this see something like CrabbyAVIF. All the parser code is rust, but it delegates to dav1d for the actual codec portion

Of the 3 software AV1 encoders, the only one that is fully dead is the Rust encoder (rav1e). If people truly wanted memory safe encoders/decoders, they would fund and develop them.

Decoders written in Rust will be a lot slower than the equivalents in assembly.