🚀 go-pugleaf

In article <1992Nov9.200954.29542@pixel.kodak.com> jmoore@pixel.kodak.com (James H. Moore 726-0322) writes:
>I saw a brief reference to MPEG (Motion Picture Experts Group), which was
>defining a standard for digital motion pictures.  The technique that
>they were using was to do differences in the frames.  This would work 
>well for the application that I would like.  Realtime capture and playback
>of a complete screen.

Be careful not to run afoul of some of the basic assumptions of JPEG
and MPEG.

MPEG, and most modes of JPEG, carry out lossy compression.  That is,
the replayed image has slightly different red/green/blue (or YUV)
intensities in the pixels than the original image, but the differences
are small enough such that a continuous-tone image looks acceptable to
the human eye.

However, computer screens (X PseudoColor/StaticColor visual classes,
and VGA images, for example) aren't continuous tone images.  Lossy
compression garbles them pretty badly.  They're more closely related
to laser-printer or FAX images than they are to photographs and motion
pictures.

If you're recording sequences of television images, MPEG might be a
good choice.  To get a look at what it can do, run down to your local
Sears or expensive-gadget store and get a demo of the CD/I (Compact
Disc Interactive) device put out by Phillips.  Some of the motion
pictures in CD/I use 1.15 megabit-per-second MPEG.

Half an hour of MPEG will take a little over half a gigabyte of data.

I don't know of any reasonably priced real-time MPEG encoding
equipment on the market.  Any MPEG encoders currently available
(November 1992) are either slower-than-real-time or costing in the six
figures, at least.  But things are happening fast in this area.

If you're recording what shows up on screen during an interactive
session, you might consider compressing the screen information with
some lossless image compression scheme.

>I am looking for
>applications which would record the output to the screen, which could be 
>"played back". 

Highland Software, Palo Alto, store@hisoft.infocomm.com (no business
relationship to me) has a software package to record and play back X
demos.  Recording is carried out by protocol interposition (a la
xscope).  This may be closer to what you want.  It certainly generates
a more compact recording.


Ollie Jones