Edited to add:
Here is the link to the list (so far) of schools that will use VITA. If one of them is a school you're applying to, go visit their web page to see if it is optional or mandatory.
Medical Schools Participating in the AAMC Video Interview Tool for AdmissionsAAMC Video Interview Tool for Admissions (AAMC VITA™)—launched in collaboration with AAMC member medical schools—will be used by medical schools to supplement alternatives to in-person interviews this year.students-residents.aamc.org
Depressingly long list