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APPENDIX
343
Motion JPEG
The JPEG compression scheme works by compressing each frame in a
video sequence. It is not the most efficient in regard to file sizes, but by
compressing every frame individually, it offers the best quality and is the
scheme of choice for people wanting to output back to video tape or
broadcast. To do this, however, you will need a lot of storage space and a
high-end video capture board that can handle large amounts of data and
low compression ratios, such as 2:1 (every one original frame can be
resized down by half). Once you get up to higher ratios such as 10:1 or
even 100:1, noticeable degradation occurs and you would be better off
using another scheme such as MPEG.
MPEG
MPEG has grown out of JPEG but added more sophisticated interframe
techniques to save only the differences between keyframes – called I
frames. Currently there are two standards: MPEG I and MPEG II. MPEG
I is designed to produce ½ screen (352x240) 24-bit color, 30 frames per
second video running at approximately 170KB per second. MPEG II is
designed for full screen (720x480) 24-bit color, 60 field video running at
anywhere between 500KB to 2 MB per second. MPEG II is set to become
the standard for high quality video playback, particularly over the newer
DVD discs.
MPEG compression is a very memory intensive process and as such
currently requires hardware assistance. While this makes for great looking
video, you will be unable to play it back on any machine that doesn't have
a similar setup or an MPEG accelerator. As such, MPEG is not suitable for
CD-ROM or Internet playback, (unless you are sure your audience has
support for MPEG), but is ideal for in-house or corporate presentations.
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