DRM_SourceID
[The feature associated with this page, Windows Media Format 11 SDK, is a legacy feature. It has been superseded by Source Reader and Sink Writer. Source Reader and Sink Writer have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use Source Reader and Sink Writer instead of Windows Media Format 11 SDK, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]
The DRM_SourceID attribute contains an identifier that associates protected content with a source.
g_wszWMDRM_SourceID
WMT_TYPE_DWORD
Source identifiers are used to differentiate content that is protected in a non-standard way from content protected by using standard Windows Media DRM.