[8.5] What's the difference between preloading and prerolling?

Preloading means that the whole of a QuickTime file is read into RAM rather than being spooled from the disk in little chunks. This is the same process as preloading other castmembers. It can improve performance be reducing the amount of data that needs to be read from different parts of the disk at the same time.

Prerolling is a process specific to QT, which initializes QuickTime and prepares it for playback of a particular movie. It is an internal software call that developers of software using QT were recommended to use in earlier versions, but they often didn't without causing noticeable ill-effects. With QT2, failing to preroll is reported to cause a significant degradation of performance

Unfortunately, Director is one of those applications which doesn't preroll for QuickTime playback.

Apple have released a system extension to compensate for this and a few other problems, which is available from:

  ftp://ftp.apple.com/dts/multimedia/quicktime/MMTuner/Apple MMTuner.hqx

This is for the Macintosh only. Whether a similar fix is required or likely to be provided for QTW remains to be seen.