Comment by thayne

I'm not at all saying that it isn't worth it for ffmpeg to use assembly, but there is a tradeoff there. Ffmpeg either needs to either only support a limited number of architectures, and duplicate code for all of them, have asm implementations for the most popular architectures (probably x86(_64) and arm), and a slower, arch independent fallback implementation in c for the rest, or have asm implementations in a large number of ISAs. I'm guessing ffmpeg does the middle option, especially since this guide focuses on x86 assembly, but ffmpeg supports many other architectures.

The performance wins may very well be worth it, but it is still good to be aware of the tradeoff involved.