What is the difference between an ISAN and a V-ISAN?

The V-ISAN is an ISAN that identifies the version of an audiovisual work. The V-ISAN is structured like every other ISAN (see What is the Structure of an ISAN?)

A “work ISAN” identifying an audiovisual work has a version segment that is null (i.e. ISAN 00AE-032A-A098-0000-X-0000-0000-Z), the “version ISAN” or V-ISAN identifying a version of work has a version segment that is not null (e.g. ISAN 00AE-032A-A098-0000-X-001F-A3E7-A).