adapter. A printed circuit card that modifies the system unit to allow it to operate in a particular way. See also card.
adaptive differential pulse code modulation (ADPCM). In audio, a compression technique that computes the differences between samples and quantizes the differences in a way that changes according to the input signal. The decompressor reconstructs the signal by accumulating the differences.
ADPCM. See adaptive differential pulse code modulation.
A-law. A method of audio encoding that maps 13-bit input samples to 8-bit numbers. The decoder reverses the mapping. The mapping is nonlinear and increases the signal quality at low levels at the expense of distortion in high-level signals. See also mu-law.
algorithm. An ordered set of well-defined rules for the solution of a problem in a finite number of steps.
aliasing. In audio and video, a kind of distortion that occurs when an input is sampled too coarsely (in time or space). In audio, aliasing produces spurious signals at both ends of the input bandwidth. In video, spatial aliasing appears as image degradation around the edges and in regions of texture.
API. See application programming interface.
application programming interface (API).
(1) The interface through which an application program interacts with an access method. (2) A functional interface supplied by the operating system or by a separately orderable licensed program that allows an application program written in a high-level language to use specific data or functions of the operating system or the licensed program.
array. (1) An arrangement of data in one or more dimensions: a list, a table, or a multidimensional arrangement of items. (2) In programming languages, an aggregate that consists of data objects, with identical attributes, each of which may be uniquely referenced by subscripting.
artifact. In audio and video, a local (temporally or spatially limited) instance of distortion.
ascend. In Ultimedia Services, to back out of a chunk.
asymmetric video compression. In multimedia applications, refers to a video compressor-decompressor pair in which the compressor is complex and the decompressor is relatively simple. Often used to produce multimedia titles that are to be viewed on computers of limited computational power. Contrast with symmetric video compression.
asynchronous. (1) Pertaining to two or more processes that do not depend upon the occurrence of specific events such as common timing signals. (2) Without regular time relationship; unexpected or unpredictable with respect to the execution of program instructions.
audio device alias. Used by the audio player/recorder and movie player to choose the audio device. This mechanism allows the player to know the device name and instantiate an object for the purpose of accessing that device.
audio filter objects. In Ultimedia Services, objects used to convert various audio formats to 16-bit pulse code modulation (PCM), convert 16-bit PCM into other formats, modify the sampling rate of 16-bit PCM, convert the byte order of 16-bit PCM, and chain several of these objects together.
audio/video interleaved (AVI) file format. A RIFF file specification that permits audio and video data to be interleaved in a file. This format permits data for the separate tracks to be accessed in alternate chunks for playback or recording while maintaining sequential access on the file device.
audio-video subsystem (AVSS). A file format used by ActionMedia and ActionMedia II adapters and Intel's Digital Video Interactive (DVI) system.
AVI file format. See audio/video interleaved file format.
AVSS. See audio-video subsystem.
bandwidth. The difference, expressed in hertz, between the highest and lowest frequencies of a range of frequencies.
bindings. Language-specific macros and procedures that make implementing and using SOM classes more convenient. These bindings offer a convenient interface to SOM that is tailored to a particular programming language. The SOM Compiler generates binding files for C and C++. These binding files include an implementation template for the class and two header files, one to be included in the class's implementation file and the other in client programs.
bit map. A pixmap with 1 bit per pixel.
block. (1) Used to denote a contiguous set of numbers or bits that has a finite length, usually a block of data. (2) In AIX, the smallest unit of a file. (3) In image- or video-processing, a small rectangular area of an image (often 4 x 4, 8 x 8, or 16 x 16 in size).
buffer. (1) A routine or storage used to compensate for a difference in rate of flow of data, or time of occurrence of events, when transferring data from one device to another. (2) A portion of storage used to hold input or output data temporarily.
byte order. The order of bytes within a 16-bit or 32-bit number. In the big-endian byte ordering, the most-significant byte is at the left; little-endian byte ordering puts the most-significant byte at the right. Systems that use difference byte orderings must swap bytes as necessary.
byte swapping. The swapping of bytes, when necessary, by clients with different byte ordering than the server for pixmap or bit-map data.
card. (1) An electronic circuit board that is plugged into a slot in a system unit. See also adapter. (2) A plug-in circuit assembly.
CCITT. Acronym for the International Telegraph and Telephone Consultative Committee.
chrominance. The difference between a color component and a reference white of the same luminous intensity.
chunk. The basic building block of a RIFF file.
chunk ID. See chunk identification.
chunk identification (chunk ID). The first item within a chunk, which is a 4-character code (FOURCC) that identifies the representation of the chunk data.
chunk size. The second item within a chunk, which is a 4-character chunk size (DWORD), that specifies the size of the data field, which is the third item within a chunk.
client program. (1) An application program that invokes methods on objects that are instances of SOM classes. (2) A functional unit that receives shared services from a server. (3) In an AIX distributed file system environment, a system that is dependent on a server to provide it with programs or access to programs.(4) In AIXwindows, a software application that fills the role of the client in the traditional client-server model upon which Enhanced X-Windows and AIXwindows are based.
codec. Abbreviation for (en)coder/decoder. A compressor-decompressor pair.
color lookup table. Synonym for color map.
color map. (1) In AIX graphics, a lookup table in which each index is associated with a red, green, and blue (RGB) value. (2) In Enhanced X-Windows, a set of color cells. A pixel value indexes the color map to produce RGB-intensities. A color map consists of a set of entries defining color values that, when associated with a window, is used to display the contents of the window. (3) In AIX graphics, a lookup table that translates color indexes into RGB triplets. Synonymous with color lookup table.
Common Object Request Broker Architecture (CORBA). A standard that provides the mechanisms by which objects make requests and receive responses. It provides interoperability between applications on different machines in heterogeneous distributed environments and seamlessly interconnects multiple object systems. Developed by the Object Management Group, which included DEC; Hewlett-Packard; HyperDesk Corporation; NCR; Object Design, Inc.; and Sun MicroSystems.
composite video. A Composite Video Baseband Signal (CVBS) has all the video information in one signal. This is usually the signal type used for line in and line out on video equipment.
compression. The process of transforming a block of data into a smaller block of data from which the former can be reconstructed. See also lossy and lossless. See also encode. Contrast with decompression.
compressor. An algorithm or software or hardware entity that does compression, usually for one algorithm. Contrast with decompressor.
configuration objects. In Ultimedia Services, objects used to allow the FiletypeDetector object to know the set of possible file types and to allow applications to request an audio device in such a way that a system administrator can specify the device to use.
constant. In programming languages, a language object that takes only one specific value.
continuous-tone. Refers to an image representation in which the intensity and color components can take many values at each pixel. Usually, each component is represented by an 8-bit number at each pixel and can take 256 values. See also halftone.
conversion objects. See audio filter objects.
CORBA. See Common Object Request Broker Architecture.
crop. In multimedia applications, to trim an image or video frame to obtain a smaller image or frame.
cue. In Ultimedia Services, specifying a starting or stopping point within media for operations such as play and record.
cuepoint. A discrete position within the media track, usually used as a starting or stopping point for playing or recording.
decode. (1) To convert data by reversing the effect of some previous encoding. (2) To interpret code. See also decompression. Contrast with encode.
decoder. In multimedia, a synonym for decompressor.
decompression. A process of expanding a compact, compressed, data block into its original uncompressed form. See also decode. Contrast with compression.
decompressor. An algorithm or software or hardware entity that does decompression, usually for one algorithm. Contrast with compressor.
define. (1) In the AIX operating system, a method used to create a device instance in the customized database. It takes a device from the undefined or nonexistent state to the defined state. (2) A preprocessor statement that causes the preprocessor to replace an identifier or macro call with specified code.
delta frame (D frame). In video compression, refers to a frame that has been compressed by subtracting a prediction of the frame from the frame and processing the difference frame further.
descend. In Ultimedia Services, to proceed into a chunk beginning at the current file position or to search for a specified chunk.
dither. (1) In computer graphics, a technique of interleaving light and dark pixels so that the resulting image looks smoothly shaded from a distance. (2) In computer graphics, a similar technique of interleaving pixels of different colors (from a limited set of colors) so that the resulting image appears to have good color rendition when viewed from a distance.
DWORD. An abbreviation for 4-character chunk size. See chunk size.
encode. To convert data by the use of a code in such a manner that reconversion to the original form is possible. Contrast with decode. See also compression.
encoder. An algorithm or object that implements some form of encoding. Contrast with decoder.
enumerator. In C language or SOM, an enumeration constant and its associated value.
event. (1) An occurrence of significance to a task; for example, the completion of an asynchronous operation, such as an input/output operation. (2) A data structure representing such an occurrence. (3) A data link control command and response that passes between adjacent nodes that allows the two nodes to exchange identification and other information necessary for operation over the data link.
event handle. In Ultimedia Services, an entity through which events are sent by objects to the application. Each instance of an object, for example, a player object, has a unique event handle. The application uses this event handle as a file descriptor on which to select and query or to block events. The event handle is necessary when writing AIX Ultimedia programs that use the AIXwindows system and toolkit.
event mask. A bit string that specifies the types of events to which a device, procedure, or object responds. The bits of the event mask correspond to the different event types recognized by the object. The programmer sets the bits of the event types to be recognized to a value of 1 and the bits of those to be filtered out to a value of 0.
event queue. A queue, or time-ordered list, of events.
exposure event. An event sent to clients to inform them when contents have been lost, as when windows are obscured or reconfigured. Servers do not guarantee the preservation of window contents when they are obscured or reconfigured.
fade. In multimedia applications, to smoothly change the strength or loudness of a video or audio signal, as in fade in, fade out, fade left, fade right, fade up, and fade down.
file access objects. Objects intended to make access to files easier.
file type. (1) In the AIX operating system in a file name divided by a period, the part of the file name after the last period. (2) The kinds of files from different file systems that are supported.
flush. In Ultimedia Services file access objects, to commit changes to a file by writing the contents of file object internal buffers to a disk.
FOURCC. See 4-character code. See also chunk identification.
4-character code (FOURCC). A 32-bit quantity representing a sequence of 1 to 4 ASCII alphanumeric characters, padded on the right with blank characters.
frame. In multimedia and video, (1) an image that corresponds to a scene at a particular instant. (2) An image that is composed of two fields taken at successive instants. One field contains the even-numbered lines, and the other contains the odd-numbered lines. (3) Either of (1) or (2), plus the audio to be played while the frame is displayed.
halftone. (1) An image that uses the variation in size and density of black dots to simulate tonal gradation. (2) A similar image that uses the variation in size and density of dots of a few colors (up to 4) to simulate tonal and color gradation. See also continuous-tone.
hue. A particular color as distinct from other colors.
huffman coding. A character coding technique used to compress data.
gray scale. A scale that indicates the shades of gray between black and white that can be presented on a display device.
hertz (Hz). A unit of frequency equal to one cycle per second.
I frame. In video compression, a frame that has been compressed independently of any other frames. Also referred to as a reference frame, intra frame, or still frame.
Indeo. A family of video codecs designed by Intel and used with the AVI file format. Similar to RTV.
implementor. With System Object Model (SOM), class implementors describe the interfaces of their classes in a standard language called the Interface Definition Language (IDL).
instance. In SOM, a concrete realization of an abstract object class. Also called object instance or object.
instantiate. (1) To make an instance of; to replicate. (2) In object-oriented programming, to represent a class abstraction with a concrete instance of the class.
interleave. To arrange parts of one sequence of things or events so that they alternate with parts of one or more other sequences of the same nature and so that each sequence retains its identity.
International Organization for Standardization (ISO). An organization of national standards bodies from various countries established to promote development of standards to facilitate international exchange of goods and services, and develop cooperation in intellectual, scientific, technological, and economic activity.
ISO. See International Organization for Standardization.
Joint Photographic Experts Group (JPEG). (1) A group that worked to establish the standard for the compression of digitized continuous-tone images. (2) The standard developed by this group.
JPEG. See Joint Photographic Experts Group.
least-significant byte (LSB). In a positional representation system, a byte having the least weight used. Contrast with most-significant byte.
linear interpolation. The generation of new samples in a 1-dimensional digital signal by drawing the line segments between consecutive input samples and taking the values from the line segments at the locations of the new samples. Commonly used to change the sampling rate of audio or to change the size of an image by processing its rows and columns.
list type. In a LIST chunk, an additional field in the first 4 bytes of the data field that is a 4-character code identifying the contents of the list.
lossless. In compression, refers to a codec that introduces no distortion into the reconstructed output of the decoder.
lossy. Refers to a process that introduces some distortion into a signal. In multimedia, a lossy codec can trade off fidelity in the reconstructed output of the decoder for higher compression.
LSB. See least-significant byte.
luminance. 1) In computer graphics, the amount of light, measured in lumens, that is emitted by a picture element (a pixel) or by a particular area of a display screen. 2) In computer graphics, the brightness component in a luminance-chrominance image representation.
media handler objects. Objects useful to software that needs to play audio to an audio device, record audio from an audio device, or play video into an AIXwindows window (typically along with an audio track being played to an audio device).
metaclass. A class whose instances are classes. In SOM, any class descended from SOMClass is a metaclass. The methods a class inherits from its metaclass are sometimes called class methods (in Smalltalk) or factory methods (in Objective-C) or constructors. See also method.
method. 1) In SOM, an interface function for an object. 2) A combination of a procedure and a name, such that many different procedures can be associated with the same name. 3) In object-oriented programming, invoking a method of an object causes the object to execute a specific method procedure. The process of determining which method procedure to execute when a method is invoked on an object is called method resolution.
monochrome. Consisting of a single color.
most-significant byte (MSB). In a positional representation system, a byte having the largest weight used. Contrast with least-significant byte.
MSB. See most-significant byte.
mu-law. In Ultimedia Services, an audio format that maps 14-bit input samples to 8-bit values. Similar to A-law.
multimedia. Material presented in a combination of text, graphics, video, animation, and sound.
NTSC. National Television Standards Committee (USA) or National Television Systems Committee. A television standard with 60 fields per second, 30 frames per second, and 525 lines per frame. Variations of the standard include NTSC-M. A size used to digitize NTSC is 640x480 pixels. This standard is used in parts of America and Japan.
null-terminated. Having a zero byte at the end. In the C language, character strings are stored this way internally.
object. In Ultimedia Services, a software abstraction consisting of data and routines that operate on the data. Users interact with objects through calls to the routines of the object. See also instance.
object-oriented programming (OOP). A method for structuring programs as hierarchically organized classes describing the data and operations of objects that may interact with other objects.
offset. The number of measuring units from an arbitrary starting point in a record, area, or control block, to some other point.
OOP. See object-oriented programming.
OR. A logic operator having the property that if P is a statement, Q is a statement, R is a statement, and so on, the OR of P, Q, R, and so on is true if at lease one statement is true and false if all statements are false.
phase alternation line (PAL). A television standard with 50 fields per second, 25 frames per second, and 625 lines per frame. Variations of the standard include PAL-B/G. A size used to digitize PAL is 768x576 pixels. This standard is used in parts of Africa, Australia, parts of Europe, and in the U.K.
PAL. See phase alternation line.
parse. To break a data stream into its component parts according to a grammar.
PCM. See pulse code modulation.
pixel. An abbreviation for picture element. One sample in a digitized image.
pixmap. An abbreviation for pixel map, which is a 3-dimensional array of bits. A pixel map can be thought of as a 2-dimensional array of pixels, with each pixel being a value from 0 to 2N - 1, where N is the depth of the pixel map.
preroll. In multimedia, the initiation of processing (usually decompression) of data streams before the desired time for the start of playback so that the playback can start properly at that time.
pulse code modulation (PCM). In data communication, variation of a digital signal to represent information. In audio, refers to simple quantization of each sample in an audio signal, with no further processing. See also adaptive differential pulse code modulation and quantization.
quantization. The subdivision of the range of values of a variable into a finite number of nonoverlapping, but not necessarily equal, subranges or intervals, each of which is represented by an assigned value within the subrange.
raster. (1) In computer graphics, a predetermined pattern of lines that provides uniform coverage of a display space. (2) The coordinate grid that divides the display area of a display device.
Real-Time Video (RTV). A video codec that first appeared in Intel's Digital Video Interactive (DVI) multimedia system.
resolution. In computer graphics, a measure of the sharpness of an image, expressed as the number of lines and columns on the display screen or the number of pixels per unit of area.
Resource Interchange File Format (RIFF). In Ultimedia Services, a standard file format used for storing multimedia files. RIFF enables audio, image, animation, and other multimedia elements to be stored in a common format. See also chunk.
RGB. (1) Color coding in which the brightness of the additive primary colors of light, red, green, and blue, are specified as three distinct values for each pixel of an image. (2) Pertaining to a color display that accepts signals representing red, green, and blue.
RIFF. See Resource Interchange File Format.
RISC. Acronym for reduced instruction-set computer.
S-Video. A representation of video information that separates the luminance (brightness) from the chrominance (color) and provides a cleaner picture than a composite video (luminance and chrominance combined) signal provides.
sample rate. In sampling, the rate at which the samples occur.
sampling. The conversion of an analog signal, varying continuously in time, into a sequence of numbers (or samples) that represent the signal values at discrete moments in time. The numbers can take arbitrary values and have not been converted to digital form. See also quantization.
scale factor. A number used as a multiplier in scaling; for example, a scale factor of 1/1000 would be suitable to scale the values 856, 432, -95, and -182 to lie in the rang -1 to +1 inclusive.
scaling. In computer graphics, enlarging or reducing all or part of a display image by multiplying the coordinates of the image by a constant value.
semantic. The relationships of characters or groups of characters to their meanings, independent of the manner of their interpretation and use.
signed. (1) Describes a quantity that can be positive, zero, or negative. (2) A binary representation of a number in which the most-significant bit represents the sign of the number and the remaining bits represent its absolute value. Contrast with unsigned.
speed factor. In Ultimedia Services, a percentage of the normal speed; for example, a percentage of the speed at which a media was recorded or is to be played.
step. In Ultimedia Services, to skip forward or backward a specified number of frames at a time. Negative frame counts move backward in the media; positive frame counts move forward.
structure. A variable that contains an ordered group of data objects. Unlike an array, the data objects can have varied data types.
symmetric video compression. In multimedia, refers to a video compressor-decompressor pair in which the compressor and decompressor have similar complexity. Used to enable a personal computer to create, as well as play back, full-motion video.
synchronous. (1) Pertaining to two or more processes that depend upon the occurrence of specific events such as common timing signals. (2) Occurring with a regular or predictable time relationship.
System Object Model (SOM). An implementation of CORBA. An object-oriented programming technology for building, packaging, and manipulating binary class libraries. With SOM, class implementors describe the interfaces of their classes in a standard language called the Interface Definition Language (IDL). See also Common Object Request Broker Architecture.
time stamp. (1) To apply the current system time. (2) The value on an object that is an indication of the system time at some critical point in the history of the object.
track. In multimedia file formats, a stream of one type of information; for example, video frames or mono or stereo audio.
two's complement. A binary number representation that allows the same implementations of arithmetic operations for all combinations of non-negative and negative numbers. So called because the negative of a number can by obtained by inverting the bits in its representation (the one's complement) and adding 1.
Ultimotion Matinee. A video encoder/decoder for use with software on IBM PS/2 computers. Ultimotion Matinee objects play standard Ultimotion Matinee media files.
unsigned. A binary number representation that represents only non-negative numbers. Contrast with signed.
usage binding. In Ultimedia Services, functions and macros defined in header files to be included in client programs.
video codec objects. Conversion objects that implement video compressors and decompressors.
YUV. A color image encoding scheme that separates luminance (Y) and two color signals: red minus Y (U) and blue minus Y (V). Transmission of YUV can take advantage of the eye's greater sensitivity to luminance detail than color detail.