Glossary

• AAC  

  Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. AAC generally achieves better sound quality than MP3 encoding at similar bit rates.



• alpha channel  

  The upper bits of a display pixel, which control the blending of video and graphical image data for a video digitizer component.



• alternate group  

  A set of related movie tracks (alternate tracks) that contain the same alternate group identifier in the track header.



• alternate track  

  A movie track that contains alternate data for another track. QuickTime chooses one track from an alternate group to be used when the movie is played. The choice may be based on such considerations as image quality or localization. See also track.



• API (Application Programming Interface)  

  The set of function calls, data structures, and other programming elements by which a structure of code (such as a system-level toolbox) can be accesses by other code (such as an application program).



• atom  

  The basic unit of data in a movie resource, sprite, or other QuickTime data structure. There are a number of different atom types. There are two varieties of atoms: QT atoms, which may contain other atoms, and classic atoms, which do not contain any other atoms. See also movie resource, sprite , QT atom, and classic atom.



• atom container  

  A tree-structured hierarchy of QT atoms. See also QT atom.



• atom ID  

  A 32-bit integer that uniquely identifies an atom among other child atoms of the same parent atom. The root atom has an atom ID value of 0x0001. See also child atom, parent atom , and root atom.



• atom type  

  A 32-bit value that uniquely identifies the data type of an atom. It is normally an OSType, rendered by four ASCII characters. An atom’s data type helps determine how the atom’s contents are interpreted.



• audio track  

  An alternative name for the sound track for a QuickTime file. See sound track.



• background color  

  The color of the background behind a sprite or other image.



• bit depth  

  The number of bits used to encode the color of each pixel in a graphics buffer.



• chapter list  

  A set of named entry points into a movie, presented to the viewer as a text list.



• child atom  

  A QT atom inside a container atom, which is its parent atom. See also QT atom, container atom , and parent atom.



• chunk  

  A collection of sample data in a media. Chunks, which may contain one or more samples, allow optimized data access. Chunks in a media may have different sizes, and the samples within a chunk may have different sizes.



• classic atom  

  A QuickTime atom that contains no other atoms. A classic atom, however, may contain a table. An example of a classic atom is an edit list atom, containing the edit list table. Compare QT atom.



• clipped movie boundary region  

  The region that combines the union of all track movie boundary regions for a movie, which is the movie’s movie boundary region, with the movie’s movie clipping region, which defines the portion of the movie boundary region that is to be used. See also movie boundary region and movie clipping region.



• clipping  

  The process of defining the boundaries of a graphics area.



• closed caption track  

  The closed caption text for a QuickTime movie, which is typically a direct transcription of a sound track and which is stored in a track with a media handler type of 'clcp'.



• container atom  

  An atom that contains other atoms, possibly including other container atoms.



• creator signature  

  In the Macintosh file system, a four-character code that identifies the application program to which a file belongs.



• data fork  

  In a legacy two-fork Macintosh file, the section that corresponds to a DOS/Windows file.



• data handler  

  A piece of software that is responsible for reading and writing a media’s data. The data handler provides data input and output services to the media’s media handler. See also media handler.



• data reference  

  A reference to a media’s data.



• decoder delay  

  The number of “pre-roll” audio samples needed to reproduce the source audio signal in an encoded audio stream for a given time index. See also encoder delay.



• display coordinate system  

  The QuickDraw graphics world, which can be used to display QuickTime movies, as opposed to the movie’s time coordinate system, which defines the basic time unit for each of the movie’s tracks. Compare time coordinate system.



• dithering  

  A technique used to improve picture quality when you are attempting to display an image that exists at a higher bit-depth representation on a lower bit-depth device. For example, you might want to dither a 24 bits per pixel image for display on an 8-bit screen.



• dropframe  

  A synchronizing technique that skips time codes to keep them current with video frames.



• duration  

  A time interval. Durations are time values that are interpreted as spans of time, rather than as points in time.



• edit list  

  A data structure that arranges a media into a time sequence.



• edit state  

  Information defining the current state of a movie or track with respect to an edit session. QuickTime uses edit states to support undo facilities.



• effect description  

  A data structure that specifies which component will be used to implement an effect in a movie, and how the component will be configured.



• effect track  

  A modifier track that applies an effect (such as a wipe or dissolve) to a movie. See modifier track.



• encoder delay  

  The term used to describe the delay incurred during encoding to produce properly formed, encoded audio packets. See also decoder delay and Background – AAC Encoding.



• file fork  

  A section of a Macintosh file. See also data fork, resource fork.



• file preview  

  A thumbnail picture from a movie that is displayed in the Open File dialog box. See also thumbnail picture.



• fixed point  

  A point that uses fixed-point numbers to represent its coordinates. QuickTime uses fixed points to provide greater display precision for graphical and image data.



• fixed rectangle  

  A rectangle that uses fixed points to represent its vertices. QuickTime uses fixed rectangles to provide greater display precision.



• Flash  

  A vector-based graphics and animation technology. Flash data is exported as SWF files.



• flattening  

  The process of copying all of the original data referred to by reference in QuickTime tracks into a QuickTime movie file. This can also be called resolving references. Flattening is used to bring in all of the data that may be referred to from multiple files after QuickTime editing is complete. It makes a QuickTime movie stand-alone—that is, it can be played on any system without requiring any additional QuickTime movie files or tracks, even if the original file referenced hundreds of files. The flattening operation is essential if QuickTime movies are to be used with CD-ROM discs.



• frame  

  A single image in a sequence of images.

  For uncompressed audio, one sample from each channel. For compressed audio, a compressed group of samples whose format is dependent on the compressor.



• frame rate  

  The rate at which a movie is displayed—that is, the number of frames per second that are actually being displayed. In QuickTime the frame rate at which a movie was recorded may be different from the frame rate at which it is displayed. On very fast machines, the playback frame rate may be faster than the record frame rate; on slow machines, the playback frame rate may be slower than the record frame rate. Frame rates may be fractional.



• free atom  

  An atom of type 'free', which you can include in a QuickTime file as a placeholder for unused space.



• file type atom  

  An atom of type 'ftyp', which defines which file specifications a file is compatible with.



• graphics mode  

  The method by which two overlapping images are blended together to produce a composite image.



• graphics world  

  A software environment in which a movie track or set of images may be defined before importing them into a movie.



• handler reference atom  

  A QT atom of type 'hdlr' that specifies the media handler to be used to interpret a media. See also QT atom, media, media handler.



• hint track  

  A track in a streaming movie that contains information for a packetizer about the data units to stream. See also streaming.



• hot spot  

  An area, typically in a VR presentation, that the user can click to invoke an action.



• hypertext  

  Action media that contains a URL and takes the user to a website.



• identity matrix  

  A transformation matrix that specifies no change in the coordinates of the source image. The resulting image corresponds exactly to the source image. See also transformation matrix.



• image  

  In sprite programming, one of a sprite’s properties. See also sprite, PCM.



• image sequence  

  A series of visual representations usually represented by video over time. Image sequences may also be generated synthetically, such as from an animation sequence.



• image track  

  Any track in a QuickTime movie that contains visual images. The term particularly applies to video tracks that contain VR data.



• input map  

  A data structure that describes where to find information about tracks that are targets of a modifier track. See modifier track.



• interlacing  

  A video mode that updates half the scan lines on one pass and goes through the second half during the next pass.



• interleaving  

  A technique in which sound and video data are alternated in small pieces, so the data can be read off disk as it is needed. Interleaving allows for movies of almost any length with little delay on startup.



• ISO  

  Acronym for the International Standards Organization. ISO establishes standards for multimedia data formatting and transmission, such as JPEG and MPEG.



• Joint Photographic Experts Group (JPEG)  

  Refers to an international standard for compressing still images. This standard supplies the algorithm for image compression. The version of JPEG supplied with QuickTime complies with the baseline ISO standard bitstream, version 9R9. This algorithm is best suited for use with natural images.



• key frame  

  A sample in a sequence of temporally compressed samples that does not rely on other samples in the sequence for any of its information. Key frames are placed into temporally compressed sequences at a frequency that is determined by the key frame rate. Typically, the term key frame is used with respect to temporally compressed sequences of image data. See also sync sample. See also key frame rate.



• key frame rate  

  The frequency with which key frames are placed into temporally compressed data sequences. See also key frame.



• layer  

  A mechanism for prioritizing the tracks in a movie or the overlapping of sprites. When it plays a movie, QuickTime displays the movie’s tracks according to their layer—tracks with lower layer numbers are displayed first; tracks with higher layer numbers are displayed over those tracks.



• leaf atom  

  An atom that contains only data, and no other atoms.



• LPCM  

  Linear pulse-code modulation (LPCM) is a method of encoding audio information digitally. The term also refers collectively to formats using this method of encoding. The term pulse-code modulation (PCM), though strictly more general, is often used to describe data encoded as LPCM. LPCM is PCM with linear quantization. See also PCM.



• matrix  

  See transformation matrix.



• matte  

  A defined region of a movie display that can be clipped and filled with another display.



• media  

  A data structure that contains information that describes the data for a track in a movie. Note that a media does not contain its data; rather, a media contains a reference to its data, which may be stored on disk, CD-ROM disc, or any other mass storage device. Also called a media structure.



• media handler  

  A piece of software that is responsible for mapping from the movie’s time coordinate system to the media’s time coordinate system. The media handler also interprets the media’s data. The data handler for the media is responsible for reading and writing the media’s data. See also data handler.



• MIDI  

  Acronym for Musical Instrument Digital Interface, a standard format for sending instructions to a musical synthesizer.



• modifier track  

  A track in a movie that modifies the data or presentation of other tracks. For example, a tween track is a modifier track. See also tween track.



• movie  

  A structure of time-based data that is managed by QuickTime. A movie may contain sound, video, animation, or a combination of any of these types of data. A QuickTime movie contains one or more tracks; each track represents a single data stream in the movie. See also time-based data, track.



• movie boundary region  

  A region that describes the area occupied by a movie in the movie coordinate system, before the movie has been clipped by the movie clipping region. A movie’s boundary region is built up from the track movie boundary regions for each of the movie’s tracks. See also movie clipping region, track movie boundary region.



• movie clipping region  

  The clipping region of a movie in the movie’s coordinate system. QuickTime applies the movie’s clipping region to the movie boundary region to obtain a clipped movie boundary region. Only that portion of the movie that lies in the clipped movie boundary region is then transformed into an image in the display coordinate system. See also movie boundary region.



• movie display boundary region  

  A region that describes the display area occupied by a movie in the display coordinate system, before the movie has been clipped by the movie display clipping region. See also movie display clipping region.



• movie display clipping region  

  The clipping region of a movie in the display coordinate system. Only that portion of the movie that lies in the clipping region is visible to the user. QuickTime applies the movie’s display clipping region to the movie display boundary region to obtain the visible image. See also movie display boundary region.



• movie file  

  A QuickTime file that stores a movie and its associated data.



• movie header atom  

  A QT atom that specifies the characteristics of an entire QuickTime movie.



• movie poster  

  A single visual image representing a QuickTime movie. You specify a poster as a point in time in the movie and specify the tracks that are to be used to constitute the poster image.



• movie preview  

  A short dynamic representation of a QuickTime movie. Movie previews typically last no more than 3 to 5 seconds, and they should give the user some idea of what the movie contains. You define a movie preview by specifying its start time, its duration, and its tracks.



• movie resource  

  One of several data structures that provide the medium of exchange for movie data between applications on a Macintosh computer and between computers, even computers of different types.



• movie sprite  

  A sprite that lives in a sprite track and acts in a movie. See also sprite track.



• MPEG-4  

  An ISO standard (based on the QuickTime file format) that supports video and audio streaming. See also streaming.



• music  

  One of the QuickTime media types, in which sequences of sounds and tones are generated.



• National Television System Committee (NTSC)  

  Refers to the color-encoding method adopted by the committee in 1953. This standard was the first monochrome-compatible, simultaneous color transmission system used for public broadcasting. This method is used widely in the United States.



• node  

  Either a panorama or an object in a QuickTime VR movie.



• NTSC  

  See National Television System Committee.



• object track  

  A track in a QuickTime VR movie that contains a set of views of a VR object.



• offset-binary encoding  

  A method of digitally encoding sound that represents the range of amplitude values as an unsigned number, with the midpoint of the range representing silence. For example, an 8-bit sound sample stored in offset-binary format would contain sample values ranging from 0 to 255, with a value of 128 specifying silence (no amplitude). Samples in Macintosh sound resources are stored in offset-binary form. Compare twos-complement encoding.



• PAL  

  See Phase Alternation Line (PAL).



• packet  

  For uncompressed audio, a sample from a single channel. For compressed audio, this field has no real meaning; by convention, it is treated as 1/number-of-channels.



• panorama  

  A structure of QuickTime VR data that forms a virtual-world environment within which the user can navigate.



• panorama track  

  A track in a QuickTime VR movie that contains a panorama.



• parent atom  

  A QT atom that contains other QT atoms, which are its child atoms. See also child atom.



• Phase Alternation Line (PAL)  

  A color-encoding system used widely in Europe, in which one of the subcarrier phases derived from the color burst is inverted in phase from one line to the next. This technique minimizes hue errors that may result during color video transmission. Sometimes called Phase Alternating Line.



• playback quality  

  A relative measure of the fidelity of a track in a QuickTime movie. You can control the playback (or language) quality of a movie during movie playback. QuickTime chooses tracks from alternate tracks that most closely correspond to the display quality desired. See also alternate track.



• poster  

  A frame shot from a movie, used to represent its content to the user.



• preferred rate  

  The default playback rate for a QuickTime movie.



• preferred volume  

  The default sound volume for a QuickTime movie.



• preview  

  A short, potentially dynamic, visual representation of the contents of a file. The Standard File Package can use previews in file dialog boxes to give the user a visual cue about a file’s contents. See also file preview.



• preview atom  

  An atom of type 'pnot', which can appear in a QuickTime file to contain a movie’s file preview.



• profile atom  

  An atom of type 'prfl', which summarizes the features of a movie or track.



• property  

  Information about a sprite that describes its location or appearance. One sprite property is its image, the original bitmapped graphic of the sprite.



• PCM  

  Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals (typically audio related in QuickTime references). See also LPCM.



• QT atom  

  A QuickTime atom that contains other atoms, possibly including other QT atoms and classic atoms. A data reference atom is an example of a QT atom. Compare classic atom.



• QTMA (QuickTime Music Architecture)  

  The part of QuickTime that lets other code create and manipulate music tracks in movies.



• QTVR track  

  A track in a QuickTime movie that maintains a list of VR nodes.



• QuickDraw  

  The original Mac OS two-dimensional drawing software, used by QuickTime.



• QuickTime  

  A set of Macintosh system extensions or a Windows dynamic-link library that other code can use to create and manipulate time-based data.



• QuickTime VR  

  A QuickTime media type that lets users interactively explore and examine photorealistic three-dimensional virtual worlds. QuickTime VR data structures are also called panoramas.



• rate  

  A value that specifies the pace at which time passes for a time base. A time base’s rate is multiplied by the time scale to obtain the number of time units that pass per second. For example, consider a time base that operates in a time coordinate system that has a time scale of 60. If that time base has a rate of 1, 60 time units are processed per second. If the rate is set to 1/2, 30 time units pass per second. If the rate is 2, 120 time units pass per second. See also time base and time unit.



• resource  

  In Macintosh programming, an entity in a file or in memory that may contain executable code or a description of a user interface item. Resources are loaded as needed by a resource manager, and are identified by their type and ID number.



• resource fork  

  In a legacy Macintosh file, the section that contains resources. The use of the resource fork for storage of QuickTime media is deprecated in the QuickTime file format.



• root atom  

  The largest atom container in a hierarchy, with atom type 'sean'.



• sample  

  A single element of a sequence of time-ordered data.



• sample format  

  The format of data samples in a track, such as a sprite track.



• sample number  

  A number that identifies the sample with data for a specified time.



• SECAM (Systeme Electronique Couleur avec Memoire)  

  Sequential Color With Memory; refers to a color-encoding system in which the red and blue color-difference information is transmitted on alternate lines, requiring a one-line memory in order to decode green information.



• skip atom  

  An atom of type 'skip', which you can include in a QuickTime file as a placeholder for unused space.



• SMPTE  

  Acronym for Society of Motion Picture and Television Engineers, an organization that sets video and movie technical standards.



• sound track  

  The audio for a QuickTime file, which is stored in a track with a media handler type of 'soun'.



• sprite  

  An animated image that is managed by QuickTime. A sprite is defined once and is then animated by commands that change its position or appearance.



• sprite track  

  A movie track populated by movie sprites.



• streaming  

  Delivery of video or audio data over a network in real time, to support applications such as videophone and video conferencing. See MPEG-4.



• string atom  

  An atom in VR media that contains text.



• subtitle track  

  The subtitle text for a QuickTime movie, which is typically a translation from the language of the sound track into a different language and which is stored in a track with a media handler type of 'sbtl'.



• SWF files  

  Files that contain Flash data. See Flash.



• sync sample  

  A sample that does not rely on preceding frames for content. See also key frame.



• Systeme Electronique Couleur avec Memoire  

  See SECAM.



• temporal compression  

  Image compression that is performed between frames in a sequence. This compression technique takes advantage of redundancy between adjacent frames in a sequence to reduce the amount of data that is required to accurately represent each frame in the sequence. Sequences that have been temporally compressed typically contain key frames at regular intervals.



• text track  

  General-purpose text that displays in a QuickTime movie, which is represented as an atom of type 'text'.



• thumbnail picture  

  A picture that can be created from an existing image that is stored as a pixel map, a picture, or a picture file. A thumbnail picture is useful for creating small representative images of a source image and in previews for files that contain image data.



• time base  

  A set of values that define the time basis for an entity, such as a QuickTime movie. A time base consists of a time coordinate system (that is, a time scale and a duration) along with a rate value. The rate value specifies the speed with which time passes for the time base.



• time-based data  

  Data that changes or interacts with the user along a time dimension. QuickTime is designed to handle time-based data.



• timecode media  

  A media of type 'tmcd' that is used to store timecode data.



• timecode track  

  A movie track that stores external timing information, such as SMPTE time codes.



• time coordinate system  

  A set of values that defines the context for a time base. A time coordinate system consists of a time scale and a duration. Together, these values define the coordinate system in which a time value or a time base has meaning.



• time scale  

  The number of time units that pass per second in a time coordinate system. A time coordinate system that measures time in sixtieths of a second, for example, has a time scale of 60.



• time unit  

  The basic unit of measure for time in a time coordinate system. The value of the time unit for a time coordinate system is represented by the formula (1/time scale) seconds. A time coordinate system that has a time scale of 60 measures time in terms of sixtieths of a second.



• time value  

  A value that specifies a number of time units in a time coordinate system. A time value may contain information about a point in time or about a duration.



• track  

  A Movie Toolbox data structure that represents a single data stream in a QuickTime movie. A movie may contain one or more tracks. Each track is independent of other tracks in the movie and represents its own data stream. Each track has a corresponding media, which describes the data for the track.



• track boundary region  

  A region that describes the area occupied by a track in the track’s coordinate system. QuickTime obtains this region by applying the track clipping region and the track matte to the visual image contained in the track rectangle.



• track clipping region  

  The clipping region of a track in the track’s coordinate system. QuickTime applies the track’s clipping region and the track matte to the image contained in the track rectangle to obtain the track boundary region. Only that portion of the track that lies in the track boundary region is then transformed into an image in the movie coordinate system.



• track header atom  

  A QT atom that specifies the characteristics of a track in a QuickTime movie.



• track height  

  The height, in pixels, of the track rectangle.



• track input map  

  A structure of QT atoms that specifies how secondary data for a track is to be interpreted (clipping, blending, etc.).



• track load settings  

  Information that specifies how and when a track is to be preloaded before running in a movie.



• track matte  

  A pixel map that defines the blending of track visual data. The value of each pixel in the pixel map governs the relative intensity of the track data for the corresponding pixel in the result image. QuickTime applies the track matte, along with the track clipping region, to the image contained in the track rectangle to obtain the track boundary region. See track matte, track rectangle, and track boundary region.



• track movie boundary region  

  A region that describes the area occupied by a track in the movie coordinate system, before the movie has been clipped by the movie clipping region. The movie boundary region is built up from the track movie boundary regions for each of the movie’s tracks.



• track offset  

  The blank space that represents the intervening time between the beginning of a movie and the beginning of a track’s data. In an audio track, the blank space translates to silence; in a video track, the blank space generates no visual image. 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.



• track reference  

  A data structure that defines the relation between movie tracks, such as the relation between a timecode track and other tracks. See timecode track.



• track rectangle  

  A rectangle that completely encloses the visual representation of a track in a QuickTime movie. The width of this rectangle in pixels is referred to as the track width; the height, as the track height.



• track width  

  The width, in pixels, of the track rectangle.



• transformation matrix  

  A 3-by-3 matrix that defines how to map points from one coordinate space into another coordinate space.



• tween data  

  The data in a tween track, such as interpolation values.



• tween track  

  A modifier track that performs a specific kind of tweening, such as path-to-matrix rotation.



• tweening  

  A process interpolating new data between given values in conformance to an algorithm. It is an efficient way to expand or smooth a movie’s presentation between its actual frames.



• twos-complement encoding  

  A system for digitally encoding sound that stores the amplitude values as a signed number—silence is represented by a sample with a value of 0. For example, with 8-bit sound samples, twos-complement values would range from –128 to 127, with 0 meaning silence. The Audio Interchange File Format (AIFF) stores samples in twos-complement form. Compare offset-binary encoding.



• URL  

  The address of a website.



• user data  

  Auxiliary data that your application can store in a QuickTime movie, track, or media structure. The user data is stored in a user data list; items in the list are referred to as user data items. Examples of user data include a copyright, date of creation, name of a movie’s director, and special hardware and software requirements. See also user data list, user data item



• user data item  

  A single element in a user data list, such as a modification date or copyright notice.



• user data list  

  The collection of user data for a QuickTime movie, track, or media. Each element in the user data list is called a user data item.



• VR (virtual reality)  

  See QuickTime VR.



• Wired Sprite  

  A sprite such as a clickable button that has wired actions associated with it.