Isn't HEIF the payload and HEIC the container? (also C seems to stand for container in HEIC...).
It's confusing how people seem to use HEIF to mean container. And if HEIF is actually the container, then what is the payload in Apple's case, and what exactly is HEIC?
HEIC is an ISOBMFF 'brand' to be used inside the container to indicate that the payload's codec is HEVC (in 'Main' profile or 'Main Still Picture' profile), and that it's one still-image and not a sequence [1].
In most of the cases where the payload is the HEVC codec, the corresponding file extension is encouraged to be .heic and the MIME-type follows as well. Apple has a note about this in their transcript at WWDC 2017 [3].
It's confusing how people seem to use HEIF to mean container. And if HEIF is actually the container, then what is the payload in Apple's case, and what exactly is HEIC?