QuickTime Architecture

QuickTime comprises two managers--the Movie Toolbox and the Image Compression Manager--plus a set of built-in components. Figure 0-1 shows the relationships between these managers and components and an application that is playing a movie.

Movie Toolbox

An application gains access to the capabilities of QuickTime by calling functions in the Movie Toolbox. The Movie Toolbox lets the application store, retrieve, and manipulate time-based data in QuickTime movies. A single movie may contain several types of data. For example, a movie that contains video information may include both video data and the sound data that accompanies the video.

The Movie Toolbox also provides functions for editing movies. For example, there are editing functions for shortening a movie by removing portions of the video and sound tracks, and there are functions for extending it by adding new data from other QuickTime movies.

Image Compression Manager

Image data may require a large amount of storage space. Storing a single 640-by-480 pixel image in 32-bit color can require as much as 1.2 MB. A sequence of images, like those contained in a QuickTime movie, demands many times as much space. As a result, minimizing the storage requirements for data is an important consideration for any application that works with images.

The Image Compression Manager provides a device-independent and driver-independent means of compressing and decompressing images and sequences of images. It also contains a simple interface for implementing external software and hardware image-compression algorithms. It provides system integration functions for storing compressed images as part of Macintosh PICT or Windows DIB files, and it offers the ability to automatically decompress compressed PICT files on any QuickTime-capable computer.

In most cases, applications use the Image Compression Manager indirectly by calling Movie Toolbox functions or by displaying a compressed picture. However, if an application compresses images or makes movies with compressed images, it may call some Image Compression Manager functions directly.

The Image Compression Manager is described in "Image Compression Manager."

QuickTime Components

Apple ships a number of built-in components with QuickTime. The built-in components provide essential services to applications and to the managers that make up the QuickTime architecture. The Apple-defined component types include image processors, media handlers, and miscellaneous utilities.

Data Processors

QuickTime's built-in data processing components perform these tasks:

movie controller components let applications play movies through a standard user interface
image compressor components compress and decompress image data
image compression dialog components let the user specify the parameters for compression operations
image transcoder components convert compressed files from one format to another
video digitizer components let applications control video digitization by external devices
data-exchange components let applications move various types of data in and out of a QuickTime movie
video output components convert QuickTime movies into video streams
graphics import components bring still graphics into QuickTime movies
music components process and synthesize music tracks in QuickTime movies
effects and transitions components implement the 133 SMPTE standard effects in QuickTime movies
preview components are used by the Movie Toolbox's standard file preview functions to display and create visual previews of file contents

Media Handlers

QuickTime's built-in media handling components perform these tasks:

derived media handler components let QuickTime support new types of data in QuickTime movies
sprite media handler components create sprite animation tracks for QuickTime movies
tween media handler components create modifier tracks that send interpolation data to other movie tracks

Utilities

QuickTime's built-in utilities perform these tasks:

clock components provide timing services for applications that use QuickTime
the Standard Sound component lets an application present the user with a dialog for configuring sound settings
sequence grabber components let applications preview and record video and sound data as QuickTime movies
sequence grabber channel components manipulate captured data for sequence grabber components
text channel components are sequence grabber channel components for text
sequence grabber panel components let sequence grabber components obtain configuration information from the user for a particular sequence grabber channel component

The process of creating custom components is described in "Component Manager" and in the sections that cover specific component types.