The afconvert utility shipped with MacOS supports muxing of FLAC
in CAF, see afconvert help output on a recent Mac here:
https://hydrogenaud.io/index.php?topic=122509.0 A file created
with afconvert free of copyright (licensed CC0) can be found here:
http://www.audiograaf.nl/misc_stuff/afconvert-FLAC-in-CAF.caf