DVDRemaster is a utility for Mac OS X to recompress large DVDs so that they fit on standard DVD5. It can either copy an entire DVD and keep all tracks, copy the main feature only, or (in the Pro version) copy selected audio and video tracks only.
This is the demonstration version. There is no limit on how long you can use it, or how much data can be recompressed, but the image will be crippled for 5 seconds every minute.