Binary size was a concern, so excessive inlining was undesirable.
And don't forget that any asm-optimized variant always has a C fallback for generic platforms lacking a hand-optimized variant which is also used to verify the asm-optimized variant using checkasm. This might not be linked into your binary/library (the linker eliminated it because it's never used), but the code exists nonetheless.
hm, fair enough. IIRC JPEG XL was a few hundred KB of SIMD code for the four or so different targets/ISAs, including the generic fallback, but I can believe video codecs are larger.
And don't forget that any asm-optimized variant always has a C fallback for generic platforms lacking a hand-optimized variant which is also used to verify the asm-optimized variant using checkasm. This might not be linked into your binary/library (the linker eliminated it because it's never used), but the code exists nonetheless.