Xref: utzoo comp.sys.mac.hardware:2528 comp.sys.mac:51461 rec.video:11382
Path: utzoo!attcan!uunet!dino!ux1.cso.uiuc.edu!tank!mimsy!mojo!hsu
From: hsu@eng.umd.edu (Dave "bd" Hsu)
Newsgroups: comp.sys.mac.hardware,comp.sys.mac,rec.video
Subject: Re: MacII and video editors and compressors, is 48 to 1 possible?
Keywords: video compression macII
Message-ID: <1990Mar27.152450.4870@eng.umd.edu>
Date: 27 Mar 90 15:24:50 GMT
References: <39830@apple.Apple.COM>
Sender: news@eng.umd.edu (The News System)
Organization: Smurfbusters!
Lines: 44

In article <39830@apple.Apple.COM> jrg@Apple.COM (John R. Galloway Jr.) writes:
>	Recently I saw on some PBS computer show (The Computer Cronicles I
>think) an issue on desktop video.  They had a piece on a very high end
>MacII based video editor (about $80K) though no mention of what extra hw
>it was using (and I do not remember the manufacturer).  You read in your
>tape (looked like std VHS) did all the editing from disk, then made a new

This sounds a lot like the Avid Technologies edit system.  They use a
modular deck controller system so you have your choice of source and
target decks, although U-Matic seems to be their favorite.

> The claim was that it took 600MB of disk to store 20 mins of video.
>At 30 512 by 512 by 24 (full) frames per second thats only 16KB per (full)
>frame or a compression ratio of about 48 to 1.

Except that this is a _video_ editor, not a film editor.  30 fps, not 24.
You can't reasonably expect 512x512 anyway from NTSC video, and you don't
need it for editing anyway; a field freeze is sufficient.  Let's say that
100x75 is the minimum tolerable size for a display window.  As nice as 24
bits may be, you can get by okay with 8 or so.  Multiply it out, and you
get 44 minutes of cheezy, uncompressed video on a 600Mb drive, eating
225kb/sec.

Now look at your limiting factors in a stock Mac II.  You can realistically
get a little better than one Mb/sec off the disk without clobbering the OS.
A Mac IIx grinds along at a couple MIPS, so you'll have no trouble getting
data to the screen, but there really isn't the power to do much decompression.
With some sensible buffering to cover up disk seeks, you can safely fly about
500kb/sec of raw video data, enough room to run two 145x110 display windows
at a time and two 10kHz sample rate 8 bit audio channels to boot, without
using any compression and without adding any hardware.

Back to your original question, I recall that Sarnoff Labs had announced
an experimental video compression chipset as part of their CD-I stuff in
late '86 which achieved between 50:1 and 200:1 compression ratios.  No
idea how well it worked, nor how good it looked.

-dave

--
Dave Hsu	 Systems Research Center, Building 115    (301) 454 8867
hsu@eng.umd.edu  The Maryversity of Uniland, College Park, MD 20742-3311

"I'm fishing.  No I'm not, I'm newting!"  - A. A. Milne