Asymmetric encryption

180 words Limit on
Bob and Alice need to send each other high-definition video files. These need to be encrypted but they are concerned that asymmetric encryption might prove too slow. However, they live too far apart to be able to safely share a symmetric encryption key.
Explain how Bob and Alice might use an asymmetric encryption system to produce a session key and whether that will solve their problems. Can they re-use the session key?