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HEIC is a container, not a codec. You can put an avif in there if you want to.

You have that backwards. HEIF is the container format. HEIC is a HEIF file using HEVC.

True, but almost everybody that says HEIC these days means HEIF, in my experience.

HEIF is a container not a codec. HEIC is HEIF + HEVC.

AVIF and HEIC both use HEIF