ClassID, Filetype and Subtype

All plug-in types that support media must identify unique classID, filetype, and subtype.

These are all four character codes, or ‘fourCCs’.

Identifier Purpose

Identifies the plug-in’s associated file type(s).

Plug-ins create lists of filetypes they support.


Differentiates between files of the same filetype.

Identifies the codec or compression to be used.


With the new editing mode system starting in CS4, the classID is far less important.

It is used as part of the identification for exporters in the Editing Mode XML.

And plug-ins may share information with most other plug-ins running in the same process using the ClassData Functions.