If
the CTOC_HF_MEDSUBTYPE flag is present in the ulHeaderFlags field
of the CTOC header (MMCFINFO), then
the ulMedUsage field of each CTOC table entry (MMCTOCENTRY) contains
a four-character code that is a media element subtype. If the flag is not
set, the ulMedUsage field is simply 32 bits of information, which
is defined by the form type.