[ffmpeg] use nasm instead of yasm

[mcmtroffaes]

• What does your PR fix? Yasm is no longer being actively maintained, so it seems like a good idea to switch to nasm since upstream supports it. Patch also replaces the deprecated --enable-yasm option with --enable-x86asm.

• Which triplets are supported/not supported? Have you updated the CI baseline? No changes.

• Does your PR follow the maintainer guide? Yes, to the best of my knowledge.

[JackBoosY]

I did the same job as a42d9e7, so when we merged one of these 2 PRs and the other should resolve the file conflict.

[mcmtroffaes]

Yep, that's swell, thanks @JackBoosY!

[JackBoosY]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[JackBoosY]

I will check the 86-windows manually later.

[JackBoosY]

When building ffmpeg:x86-windows:

LD	libavcodec/avcodec-58.dll
   Creating library libavcodec/avcodec.lib and object libavcodec/avcodec.exp
LINK : fatal error LNK1000: unknown error at 00007FF6F720AC26; consult documentation for technical support options

[mcmtroffaes]

I've done a fresh rebase and spent some time trying to diagnose this problem. For me, on the 32 bit build, the linker just hangs for a really long time (like 20 minutes) at the avcodec linking stage, and then causes the powershell terminal to crash, but I suppose it's the same error. Not sure where to go from here, except to fall back on yasm for x86... 😕 I will add a commit to this effect.

[mcmtroffaes]

Looks like this has fixed the x86 build. 🎉

[JackBoosY]

Need test features, should be good.

[mcmtroffaes]

Sure, FWIW here's my build matrix on appveyor (against a slightly more recent than version of ffmpeg compared to the one on vcpkg, but it also includes the nasm patch).

https://ci.appveyor.com/project/mcmtroffaes/ffmpeg-msvc-build/builds/37449560

[Baklap4]

@mcmtroffaes did you ever find out why it hangs on nasm in the linker phase? I was wondering if this commit was still needed in latest master. But It seems i'm running in the same problem that it just 'hangs' and doesn't do anything with nasm. I came here because of #19121 as yasm cannot be retrieved due to certificate error.

[mcmtroffaes]

@Baklap4 That's an excellent question. Unfortunately, I never found out why nasm fails with x86 on ffmpeg... I agree it would be best if we could simply phase out yasm for ffmpeg completely.