DRM_DRMHeader_ContentID
[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 It has been superseded by Source Reader and Sink Writer.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_DRMHeader_ContentID attribute contains the contentID that was generated by the content owner.
g_wszWMDRM_DRMHeader_ContentID
WMT_TYPE_STRING
This attribute is present with DRM Version 7 content only. It can be retrieved with IWMDRMReader::GetDRMProperty. To set the content ID on the file using IWMDRMWriter::SetDRMAttribute you must use the DRM_ContentID property.