Media Handlers: Sprites

Sprites are a unique type of animation entity. Most animations are based on bitmaps or vectors. Sprites are initially defined, and then animated by reference. This can result in very low-bandwidth animations of high quality. In addition, the QuickTime sprite functions automatically handle many animation chores: sprites which are "in front of" other visual elements occlude them, and they are in turn occluded by images that they pass "behind."

QuickTime sprites are especially flexible. While a sprite is typically defined originally as a bitmap, a QuickTime sprite's source data can be almost anything: MPEG video, a QTVR object, a URL, or a live video feed on the Internet.

Sprites can exist in the sprite tracks of QuickTime movies, or in Sprite Worlds of their own (for animations that exist within applications but are not part of a QuickTime movie). Sprites within movies are handled by the Sprite Media Handler. Sprites outside of movies are handled by calls to the Sprite Toolbox.

This chapter is of interest to developers who work with sprite animations and to developers who want to provide video effects that can be achieved using sprite technology.

About the Sprite Media Handler

QuickTime 3 Reference introduces several concepts necessary to add sprites to a QuickTime movie. Included is a general discussion of sprite tracks, key frame samples, override samples, sprite properties, and sprite background layers.

New Features of the Sprite Media Handler

QuickTime 3 Reference describes a new feature of QuickTime 3, the ability to use a URL as a source image for a sprite.

Key Frame Samples and Override Samples

QuickTime 3 Reference gives an overview of how sprites are defined and animated within QuickTime movies. Two different animation techniques are described: SingleOverride, in which a sample contains differences from the keyframe, and AllOverrides, in which a sample contains differences from the last sample.

Sprite Track Media Format

QuickTime 3 Reference gives a detailed description of how a sprite track's media is constructed using QuickTime Atoms.

Sprite Track Properties

QuickTime 3 Reference describes properties that can be assigned to the sprite track as a whole, instead of to individual sprites. The properties include background color, preferred bit depth, and sample format (SingleOverride or AllOverrides).

Alternate Sources for Sprite Image Data

QuickTime 3 Reference describes how to use other sources than the sprite track's keyframe to obtain a sprite's image data. This is a powerful technique that allows "sprite animation" to be used to acheive a wide variety of video effects. Image data can be obtained from a modifier track, an application (perhaps providing live video), or other sources, and then animated as a sprite.

Support for URL Linking

QuickTime 3 Reference describes how to use a URL as a source of image data for a sprite. This allows a QuickTime movie to use sprites whose images are defined elsewhere on the Internet or on an intranet. This function is particularly useful in conjunction with Macromedia's Director software.

Using the Sprite Media Handler

QuickTime 3 Reference shows in detail how to create and manipulate a sprite animation as a track in a QuickTime movie. Extensive code samples are provided. The topics covered are:

Sprite Media Handler Functions

QuickTime 3 Reference defines the functions your application uses when working with the Sprite Media Handler. The available functions are:

Constants

QuickTime 3 Reference defines the constants your application can use to communicate with the Sprite Media Handler. Included are constants that represent sprite track formats and constants that represent sprite media atom types.