[FFmpeg-devel] Re: [Question] Learning about VVC and wasm

["Rémi Denis-Courmont via ffmpeg-devel" <ffmpeg-devel@ffmpeg.org>]

Le torstaina 13. marraskuuta 2025, 19.56.30 Itä-Euroopan normaaliaika Sidd via 
ffmpeg-devel a écrit :
> Regarding the assembly, since FFmpeg is known for handcrafting it, are
> there any references of help in their docs regarding this?

Generally, the ISA should cover assembler in the specifications.

For FFmpeg, WASM optimisations are embryonic at best. There is no 
documentation since there is very little experience with them as yet.

> I have gone through their ASM lessons and know the basics of them but am
> quite far from being good at writing it.

> And if I may ask, what exactly are the current drawbacks of the current C
> implementation?

FFmpeg (and also dav1d and x264) generally dislike C intrinsic optimisations 
because:
- they are generally incompatible with run-time feature detection,
- the syntax tends to be even more cumbersome than assembler,
- the compiler may mess up the register allocation and
  perform unnecessary moves or spills,
- some functionality may not even be exposed via intrinsics.

I do not know if any of those points are relevant for WASM though.

-- 
Rémi Denis-Courmont
https://www.remlab.net/



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