Regarding "Motion JPEG" file format, I came across the following snippet at
http://www.faqs.org/faqs/jpeg-faq/part1/section-20.html:

   As was stated in section 1, JPEG is only for still images.  Nonetheless,
   you will frequently see references to "motion JPEG" or "M-JPEG" for video.
   *There is no such standard*.  Various vendors have applied JPEG to
   individual frames of a video sequence, and have called the result "M-JPEG".
   Unfortunately, in the absence of any recognized standard, they've each done
   it differently.  The resulting files are usually not compatible across
   different vendors.
   
   MPEG is the recognized standard for motion picture compression.  It uses
   many of the same techniques as JPEG, but adds inter-frame compression to
   exploit the similarities that usually exist between successive frames.
   Because of this, MPEG typically compresses a video sequence by about a
   factor of three more than "M-JPEG" methods can for similar quality.
   The disadvantages of MPEG are (1) it requires far more computation to
   generate the compressed sequence (since detecting visual similarities is
   hard for a computer), and (2) it's difficult to edit an MPEG sequence on a
   frame-by-frame basis (since each frame is intimately tied to the ones around
   it).  This latter problem has made "M-JPEG" methods rather popular for video
   editing products.
   
   It's a shame that there isn't a recognized M-JPEG standard.  But there
   isn't, so if you buy a product identified as "M-JPEG", be aware that you
   are probably locking yourself into that one vendor.
   
   Recently, both Microsoft and Apple have started pushing (different :-()
   "standard" M-JPEG formats.  It remains to be seen whether either of these
   efforts will have much impact on the current chaos.  Both companies were
   spectacularly unsuccessful in getting anyone else to adopt their ideas about
   still-image JPEG file formats, so I wouldn't assume that anything good will
   happen this time either...
   
   See the MPEG FAQ for more information about MPEG.

I'm not sure how current this FAQ is, but it agrees with what Jan wrore.

	-- John