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From: fwb@demon.siemens.com (Frederic W. Brehm)
Newsgroups: comp.misc
Subject: Re: Information Density of Sight and Sound
Message-ID: <24837@siemens.siemens.com>
Date: 27 Feb 90 15:24:18 GMT
References: <90057.153351RMC100@psuvm.psu.edu>
Sender: news@siemens.siemens.com
Reply-To: fwb@demon.UUCP (Frederic W. Brehm)
Organization: Siemens Corporate Research
Lines: 41

Randy Carraghan (RMC100@psuvm.psu.edu) asks:
>... Even using CDs, you'd only be
>able to store a minute or so of animation.  Now if you were to implement some
>sort of compression routine, you'd be able to increase the number of frames
>you could store, but the playback speed would become slower than it already
>is.  How is it that two hour movies are stored on a single video disk?

Intel's DVI (invented at David Sarnoff Research Center when RCA was still
around) achieves a 160 to 1 compression ratio for full motion video (TV
quality).  This allows a full hour of video to be put on a CD.  Intel has
some plug-in boards for AT computers that allow playback (decompression) in
real-time.  Compression could not be done in real-time, the last I heard.
The latest Electronics magazine has articles on "Multi-media" systems,
including DVI, CD-I, and Apple's systems.

The video disk is the name given by RCA to their disk.  It could store one
hour of uncompressed video.  The laser disk (Phillip's video disk) stores
uncompressed video, too.  It has several different modes that trade time
for random access or other capabilities, but it does not use image
compression.

Both of these video disks store images in an analog form, not digital.
Their bandwidth is sufficient for storing analog TV images (because the
disks were designed that way!).  Errors in the analog world are called
"noise".  People are used to seeing some noise on their TV screen, so the
disks were not designed with analog error detection or correction (besides,
how would you do that?).  The analog disks were designed to have
"acceptable" (as defined by someone) noise levels.  Their digital
counterparts have error detection and correction to provide a nearly
error-free (noisless) digital signal.

An analog signal converted to digital and then modulated for transmission
over an analog channel requires more bandwidth than the original analog
signal.  Add error detection and correction to the digital signal and you
need even greater channel bandwidth.  This is why your calculations would
lead you to believe that the laser disk can't work at full speed!

Fred
--
Frederic W. Brehm	Siemens Corporate Research	Princeton, NJ
fwb@demon.siemens.com	-or-	princeton!siemens!demon!fwb