MJPEG, or Motion-JPEG, is a standard
codec for encoding video clips,
popular with many video capture cards, such
as IOMega Buz, the Miro DC series of cards,
and the LML33, Matrox Marvel,
all using a Zoran chip, and the
multitude of cards using the Brooktree BT848
chip.
As the name suggests, the video clip is
basically stored as a series of JPEG images.
MJPEG is not a file format however,
but needs to be encapsulated in
another format. Both AVI and
QuickTime movies support the MJPEG
codec.
As the frames of an MJPEG stream consists of whole
pictures, no temporal compression can be done,
and the result is a very large movie file.
With 25% JPEG quality and standard PAL
format (720x576), I ended up on approximately
4 - 5 gigabytes per hour recorded. So, if
you're low on disk space, re-encoding to an
MPEG 1 or 2 stream is usually a good idea.