🚀 go-pugleaf

Hi.  "How much {picture,sound} time can ya fit on a CD?" is a
deceptively complicated question.  CD-I and DVI use the same
underlying medium (as do CD-DA and CD-ROM, fundamentally) but make
different choices about how to use the bandwidth.  The disc can hold
about 640Kb of "stuff", in any case.  As far as video goes, DVI uses
fancy (and very proprietary) compression/ decompression to allow
sustained full-screen, full-motion pictures.  I think the compression
factor varies in some way with the material, from a low of 10:1 to a
high of about 100:1.  (Can anybody do a better job on that?  Please
followup!)  Although decompression can be done in real time, with
Intel's 2-chip set, compression is a mainframe mega-cycles kind of
proposition, with supercomputer-class machines ideal.

CD-I doesn't specify any video compression, so is unable to support
full-screen, full-motion rates: there just ain't enough raw bits
flowing off the disc to get it.  You can have full-motion partial
screen video (to a max of about 1/3 of the screen), or "slow-scan"
styled jerky full-screen video - about 8 or 10 frames/sec, if I
remember correctly.  (I'm dipping 'way back on this stuff.  I worked
on a CD-I authoring system about 2 1/2 years ago while I was in the
Advanced Development / New Media Workstation group at Sun; the work was
done under contract for Philips, who, along with Sony, is the source
of all the CD-xx standards.  The stuff I'm saying may be wrong based
on revs to the Green Book which I don't know about.  Of course, it may
also be bogus because - in my mom's words - "I'm up to the 'z' in
Altzheimer's!")

CD-I does a much better job on audio.  It supports 4 or 5 different
encodings, ranging from CD-DA tracks on a CD-I disc, to an encoding
which uses half that space and bandwidth, giving twice the time, all
the way to a "voice-grade mono" encoding which would allow 20 hours of
sound.  Most listeners can't tell the difference between the CD-DA and
the half-rate encoding.  Although the sound quality of the most
efficient encoding is noticibly tinny for music, it's just fine for
voice information.  The other encodings I haven't identified lie
between those extremes, and can be used to juggle time-space and audio
quality in situations where the listener's attention is more-or-less
taken up with visual data.  CD-I's audio encoding doesn't have nearly
the compute-time requirements as DVI's video encoding, and has been
done successfully on PC-class authoring stations.

For slide-show styled titles, using a combination of still video
images, computer-generated box-and-arrow markup, cartoon graphics
animation, and voice-over, CD-I will be a terrific medium.  For things
which want a lot of whizzy full-motion video, DVI will probably do a
better job.  Both of them will do a better job than the current
platform-dependent CD-ROMs will.  (There is another flavor of
Sony-Philips disc which adds CD-I audio encoding to the CD-ROM
standard, but the thing is still highly platform-dependent.)  DVI
shares the same platform-dependence as CD-ROM, at least in theory, but
the new 2-chip set should make the appearence of dedicated DVI players
economically possible.  CD-I was designed from the start as
mass-market consumer technology.  The question will, I bet, finally
work out to a question of time-to-market and title production.  Both
media are usable, neither is perfect.  Both benefit from the economies
of scale generated by the success of consumer CD-DA technology, which
has not been available to the "big-disk" videodisk marketplace.

By the way, I would very much appreciate pointers to companies and
organizations working in computer-based new media in the Portland, OR,
area.  I miss working with this stuff, and would like to find out
what's going on around here.  Tanx.

		Paul
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Paul Weiss                <- Mangler, systems software, Intel/CMU iWarp project
pweiss@iWarp.intel.com    <- I wouldn't even try the "reply" key, were I you.
(503)629-6371             <- ... as in "webby feets"
Standard disclaimer: Yep. <- Strange powers speak through me, but Intel doesn't
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-------------------------------------------------------------------------------
Paul Weiss                <- Mangler, systems software, Intel/CMU iWarp project
pweiss@iWarp.intel.com    <- I wouldn't even try the "reply" key, were I you.
(503)629-6371             <- ... as in "webby feets"