file-heif: export dialog should only offer file formats supported by the libheif it has loaded at runtime
there are 2 functions in a recent libheif to query what formats are supported:
heif_have_decoder_for_format
heif_have_encoder_for_format
It is possible to compile libheif without HEVC but with AV1, basically making it a libavif. But you can drop in a libheif that supports both later on.
While reviewing the code I noticed the comment in https://gitlab.gnome.org/GNOME/gimp/-/blob/master/plug-ins/common/file-heif.c#L1718 is wrong. It only sets up the encoder and not actually encodes the file there.
Edited by darix