From: ldo@waikato.ac.nz (Lawrence D'Oliveiro, Waikato University)
Newsgroups: comp.multimedia
Subject: QuickTime (was Re: Buying a multimedia system)
Date: 9 Sep 92 18:38:55 +1200
Organization: University of Waikato, Hamilton, New Zealand

In article <1992Sep8.175412.422@murdoch.acc.Virginia.EDU>, dudley@cebaf4.cebaf.gov (John Dudley) writes:
>
>  Does anyone else find it so strange that people say Mac/Multimedia
> GREAT! Lot's of software!  YET, the only thing that I have ever seen
> mentioned is QuickTime..??? (AmigaVision's direct competitor)

Perhaps a recap of what QuickTime actually is is in order.

QuickTime is Apple's multimedia extension to the Macintosh OS. It provides
a range of services to applications:

      * Routines for manipulating a standard "Movie" in-memory data structure
  	and on-disk movie file format. This includes services for creating,
	editing and playing movies.
      * Image compression services. These include a standard set of compression
	algorithms (including JPEG), with the ability to plug in others.
	Compressors can do frame-differencing on image sequences, and this
	ability is used heavily in typical movies.
      * A Component Manager for handling add-ons to the basic QuickTime
	architecture. For example, image compressors are components; you can
	implement custom compression algorithms, or alternative implementations
	of existing algorithms (e g a driver for a third-party JPEG board).
	Video digitizers are also a standard component type, which allows any
	video digitizer board to work with any application capable of accepting
	video input. In addition you can create custom component types for your
	own purposes.

A movie consists of one or more tracks. A track has an associated medium
(or "media", as the documentation insists on calling it).

The medium has a type (current standard ones are video and sound), and there
must be a corresponding handler component present on your system to handle
media of that type. The medium contains a reference to the file which holds the
data samples, and each sample has a time attached to it, relative to the
medium's time scale.

A time scale is an integer number, representing the granularity with which
time can be measured in the medium or movie. For example, a time scale
of 1000 indicates that time is being measured in units of 1/1000 second.

A track basically maps the samples from the medium's time scale to the movie's
time scale. The track contains a sequence of edits, each mapping a contiguous
portion of media time to movie time. A track may contain empty segments, which
don't map to any valid portion of the medium (for a sound track, such segments
would appear as silence; for a video track, such segments would make no
contribution to the image displayed at that point). A part of the medium may
appear in the track more than once. Another part may not appear at all.

Tracks can be arranged into "alternate groups". For example, you might have
a number of audio voiceover tracks, each in a different language. You simply
choose the desired language in which you want to play the movie, and QuickTime
will automatically choose the right track from each alternate group. Alternate
groups can also represent the same data stored at different levels of
quality, e g 16-bit stereo sound versus 8-bit mono, 24-bit-per-pixel images
versus 1-bit-per-pixel. QuickTime will automatically select the most
appropriate track from each group, based on the hardware capabilities of your
machine.

Different movies can share common data. When you copy and paste movie segments,
you're only copying the track edit lists (and other settings), not the actual
media data. This makes editing very fast, and avoids using up disk (or RAM)
space with multiple copies of the sample data.

However, it can make it harder to distribute the final movie to someone else,
and it can also impact playback performance, if the system has to seek all
over your hard disk to fetch various segments of the movie. For this reason,
QuickTime provides "movie flattening" services that you can use once you've
finished an editing session. These copy all the data for a specified into a
new file in the right sequence, optionally interleaving it for playback
efficiency, and leaving behind all the unneeded data. The result is a
self-contained movie file that you can distribute to others.

That's a simplified description. There's quite a bit more to it than that
(like transformation matrices, the standard movie controller, and how nicely
QuickTime ties in with the existing QuickDraw graphics system), but it's
probably best if you read the QuickTime documentation for yourself. There
are already loads of applications that support QuickTime--not just multimedia-
specific ones like MacroMind Director, Adobe Premiere and DiVA VideoShop, but
even more "mainstream" ones like word processors, presentation packages and
drawing programs. There is even a neat system hack, called Wild Magic, that
lets you bring QuickTime movies into the huge base of existing applications
that only know how to display ordinary QuickDraw pictures.

Now, does that sound like AmigaVision to you?

Lawrence D'Oliveiro                       fone: +64-7-856-2889
Computer Services Dept                     fax: +64-7-838-4066
University of Waikato            electric mail: ldo@waikato.ac.nz
Hamilton, New Zealand    37^ 47' 26" S, 175^ 19' 7" E, GMT+12:00
Newsgroups: comp.multimedia