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QuickTime

From Higher Intellect Vintage Wiki

Multimedia framework developed by Apple Computer. QuickTime is Apple Computer's industry standard software architecture for creating, editing, and publishing digital media.

QuickTime is at the foundation of some of the industry's most respected digital media software tools, including Adobe After Effects, Avid Cinema, Adobe Premiere, Radius Edit, and Macromedia's much-anticipated Final Cut.

General Information

QuickTime is Apple Computer's award-winning, industry-standard, software architecture that makes it possible to create, integrate, and publish all types of digital media. Using QuickTime, software applications can offer the ability to work with a wide variety of media file formats and media encodings in an easy, consistent way. QuickTime was designed from the ground up to simplify the task of working with and integrating the widest possible range of digital media types-not just sound and video. QuickTime today truly provides the most comprehensive, most flexible, and most integrated set of media services available to content creators and software developers regardless of whether you publish to video tape, CD-ROM, or the Internet.

QuickTime is composed of three distinct elements-the QuickTime Movie file format, the QuickTime Media Abstraction Layer, and a rich set of built-in QuickTime media services. These three elements enable users to realize the full benefits of the QuickTime software architecture.

QuickTime Components

QuickTime includes several components that are provided by Apple. These components provide essential services to your application and to the managers that make up the QuickTime architecture. The following Apple-defined components are among those used by QuickTime:

  • movie controller components, which allow applications to play movies using a standard user interface
  • standard image-compression dialog components, which allow the user to specify the parameters for a compression operation by supplying a dialog box or a similar mechanism
  • image compressor components, which compress and decompress image data
  • sequence grabber components, which allow applications to preview and record video and sound data as QuickTime movies
  • video digitizer components, which allow applications to control video digitization by an external device
  • media data-exchange components, which allow applications to move various types of data in and out of a QuickTime movie
  • derived media handler components, which allow QuickTime to support new types of data in QuickTime movies
  • clock components, which provide timing services defined for QuickTime applications
  • preview components, which are used by the Movie Toolbox's standard file preview functions to display and create visual previews for files
  • sequence grabber components, which allow applications to obtain digitized data from sources that are external to a Macintosh computer
  • sequence grabber channel components, which manipulate captured data for a sequence grabber component
  • sequence grabber panel components, which allow sequence grabber components to obtain configuration information from the user for a particular sequence grabber channel component

These components and the interfaces they support are discussed in Inside Macintosh: QuickTime Components.

Movie Toolbox

QuickTime allows you to manipulate time-based data such as video sequences, audio sequences, financial results from an ongoing business operation, laboratory data recorded over time, and so on. QuickTime uses the metaphor of a movie to describe time-based data. Therefore, QuickTime stores time-based data in objects called movies.

Just as a cinematic movie can contain several tracks (for example, a video track and a sound track), a single QuickTime movie can contain more than one stream of data. Following the movie metaphor, each of these data streams is called a track. Tracks in QuickTime movies do not actually contain the movie's data. Rather, each track refers to a single media that, in turn, contains references to the actual media data. The media data may be stored on disks, CD-ROM volumes, videotape, or other appropriate storage devices.

At the most basic level, the Movie Toolbox allows you to process time-based data. As such, the Movie Toolbox must provide a description of the time basis of that data as well as a definition of the context for evaluating that time basis. In QuickTime, a movie's time basis is referred to as its time base. Geometrically, you can think of the time base as a vector that defines the direction and velocity of time for a movie. The context for a time base is called its time coordinate system. Essentially, the time coordinate system defines the axis on which the time base vector is plotted. The smallest single unit of time marked on that axis is defined by the time scale as the units per absolute second.

Tracks

A movie can contain one or more tracks. Each track refers to media data that can be interpreted within the movie's time coordinate system. Each track begins at the beginning of the movie. However, a track can end at any time. In addition, the actual data in the track may be offset from the beginning of the movie. Tracks with data that does not commence at the beginning of a movie contain empty space that precedes the track data.

All of the tracks in a movie use the movie's time coordinate system. That is, the movie's time scale defines the basic time unit for each of the movie's tracks. Each track begins at the beginning of the movie, but the track's data might not begin until some time value other than 0. This intervening time is represented by blank space--in an audio track the blank space translates to silence; in a video track the blank space generates no visual image. Each track has its own duration. This duration need not correspond to the duration of the movie. Movie duration always equals the maximum duration of all the tracks.

A track is always associated with one media. The media contains control information that refers to the data that constitutes the track. The track contains a list of references that identify portions of the media that are used in the track. In essence, these references are an edit list of the media. Consequently, a track can play the data in its media in any order and any number of times.

Media Structures

A media describes the data for a track. The data is not actually stored in the media. Rather, the media contains references to its media data, which may be stored in disk files, on CD-ROM discs, or other appropriate storage devices. Note that the data referred to by one media may be used by more than one movie, though the media itself is not reused.

Each media has its own time coordinate system, which defines the media's time scale and duration. A media's time coordinate system always starts at time 0, and it is independent of the time coordinate system of the movie that uses its data. Tracks map data from the movie's time coordinate system to the media's time coordinate system.

Each supported data type has its own media handler. The media handler interprets the media's data. The media handler must be able to randomly access the data and play segments at rates specified by the movie. The track determines the order in which the media is played in the movie and maps movie time values to media time values.

Notes

  • QuickTime has a nice undocumented feature: you can name a movie file to "Startup Movie" and put it in the System Folder, and it will be played on startup when QuickTime loads. In international system software this name will be different (in Swedish it's "Startfilm"); you can find the name it uses in STR resource -2020.

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