libheif-plugins 1.21.2 (new formula)

[cho-m]

Not sure on naming. Since compiling files in libheif/plugins just went with libheif-plugins.

Comparing with linux distros:

• Alpine supports split package and went with per-plugin (e.g. libheif-dav1d) and meta libheif-plugins-all
• Debian is similar to Alpine with per-plugin (e.g. libheif-plugin-dav1d) and meta libheif-plugins-all.

Didn't want to use libheif-plugins-all as I am excluding less popular formulae like:

1. openh264 - Rank 3777 for 80 installs in 30 days. FFmpeg seems like it can be used as alternative AVC decoder.
2. kvazaar - Rank 8223 for 10 installs in 30 days. Seems mainly available as BSD-licensed alternative to x265 to avoid GPL-ing libheif but no major benefit otherwise.
3. VVC support - vvdec (Rank 9663), vvenc (Rank 7677), uvg266 (Rank 16333). Seems uncommon enough to not support.

Enabled codecs are all in top 1000 formulae. Most are in top 150 with only rav1e being Rank 674. rav1e still seems popular enough to keep.