http://www.rfc-editor.org/rfc/rfc3803.txt
RFC 3803: Content Duration MIME Header Definition, G. Vaudreuil, G. Parsons2004-06-01T23:00:00-00:00This document describes the MIME header Content-Duration that is intended for use with any time varying media content (typically audio/* or video/*). [STANDARDS-TRACK]