WM/Track
[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 It has been superseded by Source Reader and Sink Writer.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 WM/Track attribute contains the track number of the content. This attribute is zero-based and is supported for backward compatibility. New content should use the WM/TrackNumber attribute instead.
g_wszWMTrack
WMT_TYPE_STRING
Many existing applications write the value for WM/Track as a DWORD. If you create an application that plays files from unknown sources, you should include code to handle both string and DWORD values.