Hi,
Perhaps the Playlist File section in the EMS User Guide, http://www.evostream.com/evo_evals/EMS%20User%20Guide.pdf,
can answer your question. You can mix live and recorded videos in the playlist file. The current playlist can also be manipulated on-the-fly using API commands to insert ads, change the source, program channels, or add a fallback stream in case the primary stream dies.
Cheers,
Don