Four different planes are available on the screen at any one time - a front plane for a cursor, two video planes and a background plane. You can even feed a videotape from an external source onto the back plane if you wish. By having up to 16 different audio channels, different quality levels of sound can be presented to the listener. If the sound is being played back through a mono television set, then lose the stereo and have four hours of high quality audio. If you use only one channel, then seventeen hours of perfectly clear narration or acceptable background music are available - genuine interactive audio for those who are looking for it, as well as perhaps a talking book for the blind.
Life is never straightforward.
And the world of multimedia is predictably complicated by the development of a number of rival systems. Apple's HyperCard is just the start of many exciting products for the new Macs. There is another digital multimedia system coming down the track as well. CD-I has been described in detail because the technology is available here and now it is possible to plan the production of material to known delivery dates. Furthermore the Labs say you'll still need an IBM AT or 386-based computer to run it when it does arrive, so prices for the system are being quoted in thousands of pounds, not hundreds.