Canon EOS R5 Mark II Advanced User's Manual page 458

Embedding Custom Picture Files
Custom picture files can be embedded in movie files by setting [Add
[ function] in [
Caution
Custom picture files are not embedded in RAW movies.
When you are recording both main and proxy movies, custom picture files are
embedded in proxy movies if the main movies are RAW movies (
movies are XF-HEVC S or XF-AVC S movies (
embedded in the main and proxy movie.
: Custom Picture] is set to [On].
), custom picture files are
458
File] to [On] when
). If the main