Mark,

> - Why was it decided to invent a format rather than use the existing
> Motion-JPEG standard (which I didn't know about until Bolot sent me
> these URLs):

Simply put, because we didn't quite understand everything about MJPEG and
wanted to get something into all of your hands to play with. Now that we
have something that's fast enough we'd all be more than happy if one of your
smart students would make Squeak read and write MJPEG proper ;-)

Cheers,
  - Andreas