Add Homebrew install instructions and avifdec/avifenc examples to README about libavif

[wantehchang]

Austin: Thanks for the suggestion. You also reported a bug in the Homebrew install: the man pages look to be disabled (not enabled). Do you know how to report that bug to Homebrew? If you know where the Homebrew build script (recipe?) is, we can take a look. It needs to pass the -DAVIF_BUILD_MAN_PAGES=ON option to cmake.

[yattoni]

I believe this is it https://github.com/Homebrew/homebrew-core/blob/399309bcf5f2f93c26ef1eca1fa93bea05fd0f26/Formula/lib/libavif.rb#L27-L32

based on the link from https://formulae.brew.sh/formula/libavif#default

[wantehchang]

Austin: Thank you for the link. The formula does not pass the -DAVIF_BUILD_MAN_PAGES=ON option to cmake. To do that, the formula needs to depend on the pandoc package.

The formula is also not using dav1d as the AV1 decoder. It should depend on the dav1d package and pass the -DAVIF_CODEC_DAV1D=ON option to cmake. It can further pass the -DAVIF_CODEC_AOM_DECODE=OFF option to cmake to not use libaom as the AV1 decoder.

[wantehchang]

Austin: Do you know if Homebrew has a libyuv package?

[yattoni]

I don't, sorry

[kmilos]

Do you know if Homebrew has a libyuv package?

@wantehchang Repology is your friend again 😉 https://repology.org/project/libyuv/versions

It doesn't look like it has. Maybe because of #2071...