Note [Deprecated. This API may be removed from future releases of Windows.]
mstart attribute specifies the start time of a clip, relative to the original media file.
Must be a string with the format hh:mm:ss.ff format, where hh = hours, mm = minutes, ss = seconds, and ff = fractions of seconds. Example: 1:04:30.512. Leading units can be omitted. For example, 3:00 (three minutes) and 45 (45 seconds) are both valid.
Build date: 11/16/2013