I haven’t worked with ffmpeg’s code, but I have worked with QEMU. QEMU has a lot of OOP (implemented in C obviously) that is supported by macros and GCC extensions. I definitely think it would have been better (and the code would be easier to work with) to use C++ rather than roll your own object model in C, but QEMU is quite old so it’s somewhat understandable. I say that as someone who mostly writes C and generally doesn’t like using C++.
Fabrice also wrote the Tiny C compiler, so very much his language of choice ..
For those used to the language it was seen as "lighter" and easier to add OO like abstractions to your C usage than bog down in the weight and inconsistencies of (early) C++
C has less moving parts — it’s more difficult to define a subset of C++ that actually works across all platforms featuring a C++ compiler, not to mention of all the binary-incompatible versions of the C++ standard library that tend to exist — and C is supported on a wider variety of platforms. If you want to maximize portability, C is the way to go, and you run into much fewer problems.
