SMIL - Synchronized Multimedia Integration Language (http://www.w3.org/AudioVideo/ ) - appears to be an XML method of expressing synchronized multimedia. RealNetworks released a SMIL implementation to https://www.helixcommunity.org/ recently.
It is unknown whether a Tcl binding or implementation exists at this time.
See http://www.realnetworks.com/resources/howto/smil/ for information about SMIL (pronounced the same as smile).