Comment by hereonout2

Possibly they could have added that warning, but at the same time this is a guide from the ffmpeg project, presumably for ffmpeg developers.

They lay it out quite clearly I think, but things like libavcodec are probably one of the few types of project where the benefits of assembly outweigh the lack of portability.

I'm not sure rust or zig's support for SIMD would be the project's first complaint either. Likely more concerned with porting a 25 year old codebase to a new language first.