update fmt/199 (MPEG-4 Media File) to include .m4b file extension

[leninoc]

Hi PRONOM folks,
we have a collection of audio books with .m4b extension which are identified as fmt/199 via signature (rightly), but the m4b extension is missing in that PUID. Would it be possible to add it please?
m4b is common format for audio books (used by Apple mostly), same enconding as m4a but it does support chapters and DRM (unlike m4a)
Credit to Archives NZ.

thank you for considering this,
best regards,
Jan