1.
Sun Microsystems
–
Sun contributed significantly to the evolution of several key computing technologies, among them Unix, RISC processors, thin client computing, and virtualized computing. Sun was founded on February 24,1982, at its height, the Sun headquarters were in Santa Clara, California, on the former west campus of the Agnews Developmental Center. On January 27,2010, Oracle Corporation acquired Sun by for US$7.4 billion, other technologies include the Java platform, MySQL, and NFS. Sun was a proponent of open systems in general and Unix in particular, the initial design for what became Suns first Unix workstation, the Sun-1, was conceived by Andy Bechtolsheim when he was a graduate student at Stanford University in Palo Alto, California. Bechtolsheim originally designed the SUN workstation for the Stanford University Network communications project as a personal CAD workstation and it was designed around the Motorola 68000 processor with an advanced memory management unit to support the Unix operating system with virtual memory support. He built the first ones from spare parts obtained from Stanfords Department of Computer Science, on February 24,1982, Vinod Khosla, Andy Bechtolsheim, and Scott McNealy, all Stanford graduate students, founded Sun Microsystems. Bill Joy of Berkeley, a developer of the Berkeley Software Distribution. The Sun name is derived from the initials of the Stanford University Network, Sun was profitable from its first quarter in July 1982. By 1983 Sun was known for producing 68000-based systems with high-quality graphics that were the only computers other than DECs VAX to run 4. 2BSD and it licensed the computer design to other manufacturers, which typically used it to build Multibus-based systems running Unix from UniSoft. Suns initial public offering was in 1986 under the stock symbol SUNW, the symbol was changed in 2007 to JAVA, Sun stated that the brand awareness associated with its Java platform better represented the companys current strategy. Suns logo, which features four interleaved copies of the sun in the form of a rotationally symmetric ambigram, was designed by professor Vaughan Pratt. The initial version of the logo was orange and had the sides oriented horizontally and vertically, but it was rotated to stand on one corner and re-colored purple. In the dot-com bubble, Sun began making more money. It also began spending more, hiring workers and building itself out. Some of this was because of demand, but much was from web start-up companies anticipating business that would never happen. Sales in Suns important hardware division went into free-fall as customers closed shop, several quarters of steep losses led to executive departures, rounds of layoffs, and other cost cutting. In December 2001, the fell to the 1998, pre-bubble level of about $100. But it kept falling, faster than many other tech companies, a year later it had dipped below $10 but bounced back to $20
2.
NeXT
–
NeXT was founded by Jobs after he was ousted at Apple, along with several co-workers. NeXT introduced the first NeXT Computer in 1988, and the smaller NeXTstation in 1990, the NeXT computers experienced relatively limited sales, with estimates of about 50,000 units shipped in total. Nevertheless, their innovative object-oriented NeXTSTEP operating system and development environment were highly influential, NeXT later released much of the NeXTSTEP system as a programming environment standard called OpenStep. NeXT withdrew from the business in 1993 to concentrate on marketing OPENSTEP for Mach, its own OpenStep implementation. NeXT also developed WebObjects, one of the first enterprise Web application frameworks, Apple purchased NeXT in 1997 for $429 million, and 1.5 million shares of Apple stock. As part of the agreement, Steve Jobs, Chairman and CEO of NeXT Software, returned to Apple, the founder promised to merge software from NeXT with Apples hardware platforms, eventually resulting in macOS, iOS, watchOS and tvOS. Parts of these systems incorporated the OPENSTEP foundation. In 1985, Apple co-founder Steve Jobs led Apples SuperMicro division, the Macintosh had been successful on university campuses partly because of the Apple University Consortium, which allowed students and institutions to buy the computers at a discount. The consortium had earned more than $50 million on computers by February 1984, while chairman, Jobs visited university departments and faculty members to sell Macintosh. Jobs met Paul Berg, a Nobel Laureate in chemistry, at a luncheon held in Silicon Valley to honor François Mitterrand, wet labs were prohibitively expensive for lower-level courses and were too complex to be simulated on personal computers of the time. Jobs was intrigued by Bergs concept of a workstation and contemplated starting a higher education company in the fall of 1985. Jobs division did not release upgraded versions of the Macintosh and most of the Macintosh Office, as a result, sales plummeted, and Apple was forced to write off millions of dollars in unsold inventory. Apples chief executive officer John Sculley ousted Jobs from his role at Apple. Later that year, Jobs began a struggle to regain control of the company. The board of directors sided with Sculley while Jobs took a visit to Western Europe. After several months of being sidelined, Jobs resigned from Apple on September 13,1985 and he told the board he was leaving to set up a new computer company, and that he would be taking several Apple employees from the SuperMicro division with him. He also told the board that his new company would not compete with Apple, Jobs named his new company Next, Inc. A number of former Apple employees followed him to Next, including Joanna Hoffman, Bud Tribble, George Crow, Rich Page, Susan Barnes, Susan Kare, and Danl Lewin
3.
Endianness
–
Endianness refers to the sequential order used to numerically interpret a range of bytes in computer memory as a larger, composed word value. It also describes the order of transmission over a digital link. Little-endian format reverses the order of the sequence and stores the least significant byte at the first location with the most significant byte being stored last. The order of bits within a byte can also have endianness, however, both big and little forms of endianness are widely used in digital electronics. As examples, the IBM z/Architecture mainframes use big-endian while the Intel x86 processors use little-endian, the designers chose endianness in the 1960s and 1970s respectively. Big-endian is the most common format in data networking, fields in the protocols of the Internet protocol suite, such as IPv4, IPv6, TCP, for this reason, big-endian byte order is also referred to as network byte order. Little-endian storage is popular for microprocessors, in due to significant influence on microprocessor designs by Intel Corporation. Mixed forms also exist, for instance the ordering of bytes in a 16-bit word may differ from the ordering of 16-bit words within a 32-bit word, such cases are sometimes referred to as mixed-endian or middle-endian. There are also some bi-endian processors that operate in either little-endian or big-endian mode, big-endianness may be demonstrated by writing a decimal number, say one hundred twenty-three, on paper in the usual positional notation understood by a numerate reader,123. The digits are written starting from the left and to the right, with the most significant digit,1 and this is analogous to the lowest address of memory being used first. This is an example of a big-endian convention taken from daily life, the little-endian way of writing the same number, one hundred twenty-three, would place the hundreds-digit 1 in the right-most position,321. A person following conventional big-endian place-value order, who is not aware of this ordering, would read a different number. Endianness in computing is similar, but it applies to the ordering of bytes. The illustrations to the right, where a is a memory address, danny Cohen introduced the terms Little-Endian and Big-Endian for byte ordering in an article from 1980. Computer memory consists of a sequence of storage cells, each cell is identified in hardware and software by its memory address. If the total number of cells in memory is n. Computer programs often use data structures of fields that may consist of data than is stored in one memory cell. For the purpose of this article where its use as an operand of an instruction is relevant, in addition to that, it has to be of numeric type in some positional number system
4.
Digital audio
–
Digital audio is technology that can be used to record, store, generate, manipulate, and reproduce sound using audio signals that have been encoded in digital form. A microphone converts sound to an electrical signal, then an analog-to-digital converter —typically using pulse-code modulation—converts the analog signal into a digital signal. This digital signal can then be recorded, edited and modified using digital audio tools, digital audio systems may include compression, storage, processing and transmission components. Conversion to a digital format allows convenient manipulation, storage, transmission, modern online music distribution depends on digital recording and data compression. The availability of music as data files, rather than as objects, has significantly reduced the costs of distribution. Before digital audio, the music industry distributed and sold music by selling copies in the form of records. With digital audio and online distribution systems such as iTunes, companies sell digital files to consumers. This digital audio/Internet distribution model is less expensive than producing physical copies of recordings, packaging them. An analog audio system captures sounds, and converts their physical waveforms into electrical representations of those waveforms by use of a transducer, the sounds are then stored, as on tape, or transmitted. The process is reversed for playback, the signal is amplified. Analog audio retains its fundamental wave-like characteristics throughout its storage, transformation, duplication, analog audio signals are susceptible to noise and distortion, due to the innate characteristics of electronic circuits and associated devices. Disturbances in a system do not result in error unless the disturbance is so large as to result in a symbol being misinterpreted as another symbol or disturb the sequence of symbols. A digital audio signal may be encoded for correction of any errors that occur in the storage or transmission of the signal. This technique, known as channel coding, is essential for broadcast or recorded digital systems to maintain bit accuracy, the discrete time and level of the binary signal allow a decoder to recreate the analog signal upon replay. Eight to Fourteen Bit Modulation is a code used in the audio Compact Disc. A digital audio system starts with an ADC that converts a signal to a digital signal. The ADC runs at a sampling rate and converts at a known bit resolution. CD audio, for example, has a rate of 44.1 kHz
5.
SPARCstation 1
–
The SPARCstation 1, or Sun 4/60, is the first of the SPARCstation series of SPARC-based computer workstations sold by Sun Microsystems. It had a distinctive slim enclosure and was first sold in April 1989, based on a LSI Logic RISC CPU running at 20 MHz, with a Weitek 3167 FPU coprocessor it was the fourth Sun computer to use the SPARC architecture and the first of the sun4c architecture. The motherboard offered three SBus slots and had built-in AUI ethernet,8 kHz audio, and a 5 MB/s SCSI-1 bus, the basic display ran at 1152×900 in 256 colours, and monitors shipped with the computer were 16 to 19 inch greyscale or colour. Designed for ease of production to compete with high-end PCs or Macs, the SPARCstation 1 features several distinctive design and packaging elements driven internally by system designer Andy Bechtolsheim and externally by design house frogdesign. Bechtolsheim specified that the motherboard would be the size of a sheet of paper, the external design motif includes dot-patterned cooling vents on the side which are echoed by a dimple pattern on the front face, and Sun purple feet. The SPARCstation 1 takes 30 pin SIMMs in groups of four and it can take either 1 MB or 4 MB SIMMs as long as the size is consistent within a bank. There are a total of four banks, which can give a total of 64 MB of memory. The memory bank nearest the floppy disk drive should be filled first, if not, the OpenBoot firmware will hang while memory checking. The SPARCstation 1 has space for up to two drives and one floppy drive internally. The machine will take any 50 pin SCSI-2 hard drive, the machine can connect to any SCSI CD drive, via either the SCSI connector on the back or by connecting it to any spare internal SCSI connector via a 50 pin cable. The SPARCstation 1 uses an M48T02 battery-backed RTC with RAM chip which handles the real time clock, the only problem with this chip is that the battery is internal, which means the entire chip must be replaced when its battery runs out. As all SPARCstation 1s made are now older than the life of this chip. The SPARCstation 1, 1+, IPC and SLC can run the operating systems. The SPARCstation 1+ pushed the CPU to a 25 MHz LSI L64801, upgraded the coprocessor to a Weitek 3172, the SPARCstation IPC is a version of the SPARCstation 1+ in a lunchbox style case and onboard video. The SPARCstation SLC is a version of the SPARCstation 1+ built into a monitor cabinet, the SPARCstation 2 is the machines successor and was released in 1990. SUN NVRAM FAQ OpenBoot command reference at the Wayback Machine Sun 4c class machine handbook at the Wayback Machine
6.
SunOS
–
SunOS is a Unix-branded operating system developed by Sun Microsystems for their workstation and server computer systems. SunOS1 only supported the Sun-2 series systems, including Sun-1 systems upgraded with Sun-2 CPU boards, SunOS2 supported Sun-2 and Sun-3 series systems. SunOS4 supported Sun-2, Sun-3, Sun386i and Sun-4 architectures, although SunOS4 was intended to be the first release to fully support Suns new SPARC processor, there was also a SunOS3.2 release with preliminary support for Sun-4 systems. SunOS4.1.2 introduced support for Suns first sun4m-architecture multiprocessor machines, since it had only a lock for the kernel. The last release of SunOS4 was 4.1.4 in 1994, the sun4, sun4c and sun4m architectures were supported in 4.1.4, sun4d was not supported. Sun continued to ship SunOS4.1.3 and 4.1.4 until December 27,1998, they were supported until September 30,2003. In 1987, AT&T Corporation and Sun announced that they were collaborating on a project to merge the most popular Unix flavors on the market at that time, BSD, System V and this would become System V Release 4. On September 4,1991, Sun announced that its next major OS release would switch from its BSD-derived source base to one based on SVR4, although the internal designation of this release would be SunOS5, from this point Sun began using the marketing name Solaris. The justification for this new overbrand was that it encompassed not only SunOS, even though the new SVR4-based OS was not expected to ship in volume until the following year, Sun immediately began using the new Solaris name to refer to the currently shipping SunOS4 release. Thus SunOS4.1.1 was rebranded Solaris 1.0, SunOS4.1. x micro versions continued to be released through 1994, and each of these was also given a Solaris 1. x equivalent name. In practice, these were still referred to by customers. Matching a SunOS5. x release to its corresponding Solaris marketing name is simple, for example, Solaris 2.4 incorporated SunOS5.4. There is one small twist, after Solaris 2.6, the 2. was dropped from the Solaris name, the latest Solaris release is named Solaris 11 and incorporates SunOS5.11. GUI environments bundled with earlier versions of SunOS included SunTools and NeWS, in 1989, Sun released OpenWindows, an OPEN LOOK-compliant X11-based environment which also supported SunView and NeWS applications. This became the default SunOS GUI in SunOS4.1.1, info on SunOS from OSdata Initial Solaris announcement
7.
Unix
–
Among these is Apples macOS, which is the Unix version with the largest installed base as of 2014. Many Unix-like operating systems have arisen over the years, of which Linux is the most popular, Unix was originally meant to be a convenient platform for programmers developing software to be run on it and on other systems, rather than for non-programmer users. The system grew larger as the system started spreading in academic circles, as users added their own tools to the system. Unix was designed to be portable, multi-tasking and multi-user in a time-sharing configuration and these concepts are collectively known as the Unix philosophy. By the early 1980s users began seeing Unix as a universal operating system. Under Unix, the system consists of many utilities along with the master control program. To mediate such access, the kernel has special rights, reflected in the division between user space and kernel space, the microkernel concept was introduced in an effort to reverse the trend towards larger kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a standard computer consisted of a disk for storage and a data terminal for input and output. However, modern systems include networking and other new devices, as graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse. In the 1980s, non-blocking I/O and the set of inter-process communication mechanisms were augmented with Unix domain sockets, shared memory, message queues, and semaphores. In microkernel implementations, functions such as network protocols could be moved out of the kernel, Multics introduced many innovations, but had many problems. Frustrated by the size and complexity of Multics but not by the aims and their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, M. D. McIlroy, and J. F. Ossanna, decided to redo the work on a much smaller scale. The name Unics, a pun on Multics, was suggested for the project in 1970. Peter H. Salus credits Peter Neumann with the pun, while Brian Kernighan claims the coining for himself, in 1972, Unix was rewritten in the C programming language. Bell Labs produced several versions of Unix that are referred to as Research Unix. In 1975, the first source license for UNIX was sold to faculty at the University of Illinois Department of Computer Science, UIUC graduate student Greg Chesson was instrumental in negotiating the terms of this license. During the late 1970s and early 1980s, the influence of Unix in academic circles led to adoption of Unix by commercial startups, including Sequent, HP-UX, Solaris, AIX. In the late 1980s, AT&T Unix System Laboratories and Sun Microsystems developed System V Release 4, in the 1990s, Unix-like systems grew in popularity as Linux and BSD distributions were developed through collaboration by a worldwide network of programmers
8.
Hexadecimal
–
In mathematics and computing, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, Hexadecimal numerals are widely used by computer system designers and programmers. As each hexadecimal digit represents four binary digits, it allows a more human-friendly representation of binary-coded values, one hexadecimal digit represents a nibble, which is half of an octet or byte. For example, a byte can have values ranging from 00000000 to 11111111 in binary form. In a non-programming context, a subscript is typically used to give the radix, several notations are used to support hexadecimal representation of constants in programming languages, usually involving a prefix or suffix. The prefix 0x is used in C and related languages, where this value might be denoted as 0x2AF3, in contexts where the base is not clear, hexadecimal numbers can be ambiguous and confused with numbers expressed in other bases. There are several conventions for expressing values unambiguously, a numerical subscript can give the base explicitly,15910 is decimal 159,15916 is hexadecimal 159, which is equal to 34510. Some authors prefer a text subscript, such as 159decimal and 159hex, or 159d and 159h. example. com/name%20with%20spaces where %20 is the space character, thus ’, represents the right single quotation mark, Unicode code point number 2019 in hex,8217. In the Unicode standard, a value is represented with U+ followed by the hex value. Color references in HTML, CSS and X Window can be expressed with six hexadecimal digits prefixed with #, white, CSS allows 3-hexdigit abbreviations with one hexdigit per component, #FA3 abbreviates #FFAA33. *nix shells, AT&T assembly language and likewise the C programming language, to output an integer as hexadecimal with the printf function family, the format conversion code %X or %x is used. In Intel-derived assembly languages and Modula-2, hexadecimal is denoted with a suffixed H or h, some assembly languages use the notation HABCD. Ada and VHDL enclose hexadecimal numerals in based numeric quotes, 16#5A3#, for bit vector constants VHDL uses the notation x5A3. Verilog represents hexadecimal constants in the form 8hFF, where 8 is the number of bits in the value, the Smalltalk language uses the prefix 16r, 16r5A3 PostScript and the Bourne shell and its derivatives denote hex with prefix 16#, 16#5A3. For PostScript, binary data can be expressed as unprefixed consecutive hexadecimal pairs, in early systems when a Macintosh crashed, one or two lines of hexadecimal code would be displayed under the Sad Mac to tell the user what went wrong. Common Lisp uses the prefixes #x and #16r, setting the variables *read-base* and *print-base* to 16 can also used to switch the reader and printer of a Common Lisp system to Hexadecimal number representation for reading and printing numbers. Thus Hexadecimal numbers can be represented without the #x or #16r prefix code, MSX BASIC, QuickBASIC, FreeBASIC and Visual Basic prefix hexadecimal numbers with &H, &H5A3 BBC BASIC and Locomotive BASIC use & for hex. TI-89 and 92 series uses a 0h prefix, 0h5A3 ALGOL68 uses the prefix 16r to denote hexadecimal numbers, binary, quaternary and octal numbers can be specified similarly
9.
C (programming language)
–
C was originally developed by Dennis Ritchie between 1969 and 1973 at Bell Labs, and used to re-implement the Unix operating system. C has been standardized by the American National Standards Institute since 1989, C is an imperative procedural language. Therefore, C was useful for applications that had formerly been coded in assembly language. Despite its low-level capabilities, the language was designed to encourage cross-platform programming, a standards-compliant and portably written C program can be compiled for a very wide variety of computer platforms and operating systems with few changes to its source code. The language has become available on a wide range of platforms. In C, all code is contained within subroutines, which are called functions. Function parameters are passed by value. Pass-by-reference is simulated in C by explicitly passing pointer values, C program source text is free-format, using the semicolon as a statement terminator and curly braces for grouping blocks of statements. The C language also exhibits the characteristics, There is a small, fixed number of keywords, including a full set of flow of control primitives, for, if/else, while, switch. User-defined names are not distinguished from keywords by any kind of sigil, There are a large number of arithmetical and logical operators, such as +, +=, ++, &, ~, etc. More than one assignment may be performed in a single statement, function return values can be ignored when not needed. Typing is static, but weakly enforced, all data has a type, C has no define keyword, instead, a statement beginning with the name of a type is taken as a declaration. There is no function keyword, instead, a function is indicated by the parentheses of an argument list, user-defined and compound types are possible. Heterogeneous aggregate data types allow related data elements to be accessed and assigned as a unit, array indexing is a secondary notation, defined in terms of pointer arithmetic. Unlike structs, arrays are not first-class objects, they cannot be assigned or compared using single built-in operators, There is no array keyword, in use or definition, instead, square brackets indicate arrays syntactically, for example month. Enumerated types are possible with the enum keyword and they are not tagged, and are freely interconvertible with integers. Strings are not a data type, but are conventionally implemented as null-terminated arrays of characters. Low-level access to memory is possible by converting machine addresses to typed pointers
10.
Byte
–
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of used to encode a single character of text in a computer. The size of the byte has historically been hardware dependent and no standards existed that mandated the size. The de-facto standard of eight bits is a convenient power of two permitting the values 0 through 255 for one byte, the international standard IEC 80000-13 codified this common meaning. Many types of applications use information representable in eight or fewer bits, the popularity of major commercial computing architectures has aided in the ubiquitous acceptance of the 8-bit size. The unit symbol for the byte was designated as the upper-case letter B by the IEC and IEEE in contrast to the bit, internationally, the unit octet, symbol o, explicitly denotes a sequence of eight bits, eliminating the ambiguity of the byte. It is a respelling of bite to avoid accidental mutation to bit. Early computers used a variety of four-bit binary coded decimal representations and these representations included alphanumeric characters and special graphical symbols. S. Government and universities during the 1960s, the prominence of the System/360 led to the ubiquitous adoption of the eight-bit storage size, while in detail the EBCDIC and ASCII encoding schemes are different. In the early 1960s, AT&T introduced digital telephony first on long-distance trunk lines and these used the eight-bit µ-law encoding. This large investment promised to reduce costs for eight-bit data. The development of microprocessors in the 1970s popularized this storage size. A four-bit quantity is called a nibble, also nybble. The term octet is used to specify a size of eight bits. It is used extensively in protocol definitions, historically, the term octad or octade was used to denote eight bits as well at least in Western Europe, however, this usage is no longer common. The exact origin of the term is unclear, but it can be found in British, Dutch, and German sources of the 1960s and 1970s, and throughout the documentation of Philips mainframe computers. The unit symbol for the byte is specified in IEC 80000-13, IEEE1541, in the International System of Quantities, B is the symbol of the bel, a unit of logarithmic power ratios named after Alexander Graham Bell, creating a conflict with the IEC specification. However, little danger of confusion exists, because the bel is a used unit
11.
Pulse-code modulation
–
Pulse-code modulation is a method used to digitally represent sampled analog signals. It is the form of digital audio in computers, compact discs, digital telephony. In a PCM stream, the amplitude of the signal is sampled regularly at uniform intervals. Linear pulse-code modulation is a type of PCM where the quantization levels are linearly uniform. This is in contrast to PCM encodings where quantization levels vary as a function of amplitude, though PCM is a more general term, it is often used to describe data encoded as LPCM. Early electrical communications started to sample signals in order to interlace samples from multiple telegraphy sources, the American inventor Moses G. Farmer conveyed telegraph time-division multiplexing as early as 1853. Electrical engineer W. M. Miner, in 1903, used an electro-mechanical commutator for time-division multiplexing multiple telegraph signals and he obtained intelligible speech from channels sampled at a rate above 3500–4300 Hz, lower rates proved unsatisfactory. This was TDM, but pulse-amplitude modulation rather than PCM, in 1920 the Bartlane cable picture transmission system, named after its inventors Harry G. Bartholomew and Maynard D. In 1926, Paul M. Rainey of Western Electric patented a machine which transmitted its signal using 5-bit PCM. The machine did not go into production, british engineer Alec Reeves, unaware of previous work, conceived the use of PCM for voice communication in 1937 while working for International Telephone and Telegraph in France. He described the theory and advantages, but no practical application resulted, Reeves filed for a French patent in 1938, and his US patent was granted in 1943. By this time Reeves had started working at the Telecommunications Research Establishment, the first transmission of speech by digital techniques, the SIGSALY encryption equipment, conveyed high-level Allied communications during World War II. In 1943 the Bell Labs researchers who designed the SIGSALY system became aware of the use of PCM binary coding as already proposed by Alec Reeves. In 1949 for the Canadian Navys DATAR system, Ferranti Canada built a working PCM radio system that was able to transmit digitized radar data over long distances, PCM in the late 1940s and early 1950s used a cathode-ray coding tube with a plate electrode having encoding perforations. The plate collected or passed the beam, producing current variations in binary code, rather than natural binary, the grid of Goodalls later tube was perforated to produce a glitch-free Gray code, and produced all bits simultaneously by using a fan beam instead of a scanning beam. Patent 2,801,281 filed in 1946 and 1952, another patent by the same title was filed by John R. Pierce in 1945, and issued in 1948, U. S. The three of them published The Philosophy of PCM in 1948, PCM is the method of encoding generally used for uncompressed audio, although there are other methods such as pulse-density modulation. The 4ESS switch introduced time-division switching into the US telephone system in 1976, LPCM is used for the lossless encoding of audio data in the Compact disc Red Book standard, introduced in 1982
12.
IEEE 754
–
The IEEE Standard for Floating-Point Arithmetic is a technical standard for floating-point computation established in 1985 by the Institute of Electrical and Electronics Engineers. The standard addressed many problems found in the floating point implementations that made them difficult to use reliably and portably. Many hardware floating point units now use the IEEE754 standard, the international standard ISO/IEC/IEEE60559,2011 has been approved for adoption through JTC1/SC25 under the ISO/IEEE PSDO Agreement and published. The binary formats in the standard are included in the new standard along with three new basic formats. To conform to the current standard, an implementation must implement at least one of the formats as both an arithmetic format and an interchange format. As of September 2015, the standard is being revised to incorporate clarifications, an IEEE754 format is a set of representations of numerical values and symbols. A format may also include how the set is encoded, a format comprises, Finite numbers, which may be either base 2 or base 10. Each finite number is described by three integers, s = a sign, c = a significand, q = an exponent, the numerical value of a finite number is s × c × bq where b is the base, also called radix. For example, if the base is 10, the sign is 1, the significand is 12345, two kinds of NaN, a quiet NaN and a signaling NaN. A NaN may carry a payload that is intended for diagnostic information indicating the source of the NaN, the sign of a NaN has no meaning, but it may be predictable in some circumstances. Hence the smallest non-zero positive number that can be represented is 1×10−101 and the largest is 9999999×1090, the numbers −b1−emax and b1−emax are the smallest normal numbers, non-zero numbers between these smallest numbers are called subnormal numbers. Zero values are finite values with significand 0 and these are signed zeros, the sign bit specifies if a zero is +0 or −0. Some numbers may have several representations in the model that has just been described, for instance, if b=10 and p=7, −12.345 can be represented by −12345×10−3, −123450×10−4, and −1234500×10−5. However, for most operations, such as operations, the result does not depend on the representation of the inputs. For the decimal formats, any representation is valid, and the set of representations is called a cohort. When a result can have several representations, the standard specifies which member of the cohort is chosen, for the binary formats, the representation is made unique by choosing the smallest representable exponent. For numbers with an exponent in the range, the leading bit of the significand will always be 1. Consequently, the leading 1 bit can be implied rather than explicitly present in the memory encoding and this rule is called leading bit convention, implicit bit convention, or hidden bit convention
13.
Adaptive differential pulse-code modulation
–
Typically, the adaptation to signal statistics in ADPCM consists simply of an adaptive scale factor before quantizing the difference in the DPCM encoder. ADPCM was developed in the early 1970s at Bell Labs for voice coding, by P. Cummiskey, N. S. Jayant and James L. Flanagan. In telephony, an audio signal for a single phone call is encoded as 8000 analog samples per second, of 8 bits each. The default signal compression encoding on a DS0 is either μ-law PCM or A-law PCM and these are logarithmic compression systems where a 13 or 14 bit linear PCM sample number is mapped into an 8 bit value. This system is described by international standard G.711, where circuit costs are high and loss of voice quality is acceptable, it sometimes makes sense to compress the voice signal even further. An ADPCM algorithm is used to map a series of 8 bit µ-law PCM samples into a series of 4 bit ADPCM samples, in this way, the capacity of the line is doubled. The technique is detailed in the G.726 standard, some ADPCM techniques are used in Voice over IP communications. ADPCM was also used by Interactive Multimedia Association for development of audio codec known as ADPCM DVI, IMA ADPCM or DVI4. G.722 is an ITU-T standard wideband speech codec operating at 48,56 and 64 kbit/s, before the digitization process, it catches the analog signal and divides it in frequency bands with QMF filters to get two subbands of the signal. When the ADPCM bitstream of each subband is obtained, the results are multiplexed, the decoder has to perform the reverse process, that is, demultiplex and decode each subband of the bitstream and recombine them. Referring to the process, in some applications as voice coding. It is a way to reduce the file size, the Windows Sound System supported ADPCM in. wav files. The corresponding FFmpeg audio codecs are adpcm-ms and adpcm-ima-wav
14.
A-law algorithm
–
An A-law algorithm is a standard companding algorithm, used in European 8-bit PCM digital communications systems to optimize, i. e. modify, the dynamic range of an analog signal for digitizing. It is one of two versions of the G.711 standard from ITU-T, the version being the similar µ-law, used in North America. The reason for this encoding is that the dynamic range of speech does not lend itself well to efficient linear digital encoding. The μ-law algorithm provides a larger dynamic range than the A-law at the cost of worse proportional distortion for small signals. By convention, A-law is used for an international connection if at least one uses it. μ-law algorithm Audio level compression Signal compression Companding G.711 DS0 Waveform Coding Techniques - Has details of implementation A-law implementation in C-language with example code
15.
Quantization (signal processing)
–
Quantization, in mathematics and digital signal processing, is the process of mapping a large set of input values to a smaller set. Rounding and truncation are typical examples of quantization processes, quantization is involved to some degree in nearly all digital signal processing, as the process of representing a signal in digital form ordinarily involves rounding. Quantization also forms the core of essentially all lossy compression algorithms, the difference between an input value and its quantized value is referred to as quantization error. A device or algorithmic function that performs quantization is called a quantizer, an analog-to-digital converter is an example of a quantizer. Because quantization is a mapping, it is an inherently non-linear. The set of input values may be infinitely large, and may possibly be continuous. The set of output values may be finite or countably infinite. The input and output involved in quantization can be defined in a rather general way. For example, vector quantization is the application of quantization to multi-dimensional input data, outside the realm of signal processing, this category may simply be called rounding or scalar quantization. An ADC can be modeled as two processes, sampling and quantization, sampling converts a voltage signal into a discrete-time signal. Quantization replaces each real number with an approximation from a set of discrete values. Most commonly, these values are represented as fixed-point words or floating-point words. Common word-lengths are 8-bit, 16-bit, 32-bit, and so on, quantizing a sequence of numbers produces a sequence of quantization errors which is sometimes modeled as an additive random signal called quantization noise because of its stochastic behavior. The more levels a quantizer uses, the lower is its noise power. In general, both ADC processes lose some information, so discrete-valued signals are only an approximation of the continuous-valued discrete-time signal, which is itself only an approximation of the original continuous-valued continuous-time signal. But both types of errors can, in theory, be made arbitrarily small by good design. In this second setting, the amount of introduced distortion may be managed carefully by sophisticated techniques, a quantizer designed for this purpose may be quite different and more elaborate in design than an ordinary rounding operation. It is in this domain that substantial rate–distortion theory analysis is likely to be applied, however, the same concepts actually apply in both use cases
16.
Companding
–
In telecommunication and signal processing companding is a method of mitigating the detrimental effects of a channel with limited dynamic range. The name is a combination of the words compressing and expanding, the use of companding allows signals with a large dynamic range to be transmitted over facilities that have a smaller dynamic range capability. Companding is employed in telephony and other applications such as professional wireless microphones. The dynamic range of a signal is compressed before transmission and is expanded to the value at the receiver. The electronic circuit that does this is called a compander and works by compressing or expanding the range of an analog electronic signal such as sound recorded by a microphone. One variety is a triplet of amplifiers, an amplifier, followed by a variable-gain linear amplifier. Such a triplet has the property that its voltage is proportional to the input voltage raised to an adjustable power. This type of quantization is used in telephony systems. The two most popular compander functions used for telecommunications are the A-law and μ-law functions, companding is used in digital telephony systems, compressing before input to an analog-to-digital converter, and then expanding after a digital-to-analog converter. This is equivalent to using a non-linear ADC as in a T-carrier telephone system that implements A-law or μ-law companding and this method is also used in digital file formats for better signal-to-noise ratio at lower bit rates. This is effectively a form of audio data compression. Professional wireless microphones do this since the range of the microphone audio signal itself is larger than the dynamic range provided by radio transmission. Companding also reduces the noise and crosstalk levels at the receiver, companders are used in concert audio systems and in some noise reduction schemes such as dbx and Dolby NR. The use of companding in a picture transmission system was patented by A. B. In 1942, Clark and his team completed the SIGSALY secure voice system that included the first use of companding in a PCM system. In 1953, B. Smith showed that a nonlinear DAC could be complemented by the nonlinearity in a successive-approximation ADC configuration. In 1970, H. Kaneko developed the uniform description of segment companding laws that had by then adopted in digital telephony. In the 1980s, many of the equipment manufacturers used companding when compressing the library waveform data in their digital synthesizers
17.
Lossy compression
–
In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size for storage, handling, different versions of the photo of the cat above show how higher degrees of approximation create coarser images as more details are removed. This is opposed to data compression which does not degrade the data. The amount of data reduction possible using lossy compression is often higher than through lossless techniques. Well-designed lossy compression technology often reduces file sizes significantly before degradation is noticed by the end-user, even when noticeable by the user, further data reduction may be desirable. Lossy compression is most commonly used to compress multimedia data, especially in such as streaming media. By contrast, lossless compression is required for text and data files, such as bank records. A picture, for example, is converted to a file by considering it to be an array of dots and specifying the color. If the picture contains an area of the color, it can be compressed without loss by saying 200 red dots instead of red dot. The original data contains an amount of information, and there is a lower limit to the size of file that can carry all the information. Basic information theory says there is an absolute limit in reducing the size of this data. When data is compressed, its entropy increases, and it cannot increase indefinitely, as an intuitive example, most people know that a compressed ZIP file is smaller than the original file, but repeatedly compressing the same file will not reduce the size to nothing. Most compression algorithms can recognize when further compression would be pointless, in many cases, files or data streams contain more information than is needed for a particular purpose. Developing lossy compression techniques as closely matched to human perception as possible is a complex task, the terms irreversible and reversible are preferred over lossy and lossless respectively for some applications, such as medical image compression, to circumvent the negative implications of loss. The type and amount of loss can affect the utility of the images, artifacts or undesirable effects of compression may be clearly discernible yet the result still useful for the intended purpose. Or lossy compressed images may be visually lossless, or in the case of medical images and this is because uncompressed audio can only reduce file size by lowering bit rate or depth, whereas compressing audio can reduce size while maintaining bit rate and depth. This compression becomes a loss of the least significant data. From this point of view, perceptual encoding is not essentially about discarding data, green, and 50 pixels of blue vs. red, which are proportional to human sensitivity to each component
18.
Digital signal processing
–
Digital signal processing is the use of digital processing, such as by computers, to perform a wide variety of signal processing operations. The signals processed in this manner are a sequence of numbers that represent samples of a variable in a domain such as time, space. Digital signal processing and analog signal processing are subfields of signal processing, digital signal processing can involve linear or nonlinear operations. Nonlinear signal processing is closely related to system identification and can be implemented in the time, frequency. DSP is applicable to both streaming data and static data, the increasing use of computers has resulted in the increased use of, and need for, digital signal processing. To digitally analyze and manipulate an analog signal, it must be digitized with an analog-to-digital converter, sampling is usually carried out in two stages, discretization and quantization. Discretization means that the signal is divided into equal intervals of time, quantization means each amplitude measurement is approximated by a value from a finite set. Rounding real numbers to integers is an example, the Nyquist–Shannon sampling theorem states that a signal can be exactly reconstructed from its samples if the sampling frequency is greater than twice the highest frequency of the signal. In practice, the frequency is often significantly higher than twice that required by the signals limited bandwidth. Theoretical DSP analyses and derivations are typically performed on discrete-time signal models with no amplitude inaccuracies, numerical methods require a quantized signal, such as those produced by an analog-to-digital converter. The processed result might be a frequency spectrum or a set of statistics, but often it is another quantized signal that is converted back to analog form by a digital-to-analog converter. In DSP, engineers usually study digital signals in one of the domains, time domain, spatial domain, frequency domain. They choose the domain in which to process a signal by making an assumption as to which domain best represents the essential characteristics of the signal. The most common processing approach in the time or space domain is enhancement of the signal through a method called filtering. Digital filtering generally consists of linear transformation of a number of surrounding samples around the current sample of the input or output signal. There are various ways to characterize filters, for example, A linear filter is a transformation of input samples. A causal filter uses only samples of the input or output signals. A non-causal filter can usually be changed into a filter by adding a delay to it
19.
Multimedia
–
Multimedia is content that uses a combination of different content forms such as text, audio, images, animations, video and interactive content. Multimedia contrasts with media that use only rudimentary computer displays such as text-only or traditional forms of printed or hand-produced material, Multimedia devices are electronic media devices used to store and experience multimedia content. Multimedia is distinguished from mixed media in art, for example. The term rich media is synonymous with interactive multimedia, the term multimedia was coined by singer and artist Bob Goldstein to promote the July 1966 opening of his LightWorks at LOursin show at Southampton, Long Island. Goldstein was perhaps aware of an American artist named Dick Higgins, two years later, in 1968, the term multimedia was re-appropriated to describe the work of a political consultant, David Sawyer, the husband of Iris Sawyer—one of Goldsteins producers at LOursin. In the intervening forty years, the word has taken on different meanings, in the late 1970s, the term referred to presentations consisting of multi-projector slide shows timed to an audio track. However, by the 1990s multimedia took on its current meaning, in the 1993 first edition of Multimedia, Making It Work, Tay Vaughan declared Multimedia is any combination of text, graphic art, sound, animation, and video that is delivered by computer. When you allow the user – the viewer of the project – to control what, when you provide a structure of linked elements through which the user can navigate, interactive multimedia becomes hypermedia. The German language society Gesellschaft für deutsche Sprache recognized the words significance, the institute summed up its rationale by stating has become a central word in the wonderful new media world. In common usage, multimedia refers to an electronically delivered combination of media including video, still images, audio, much of the content on the web today falls within this definition as understood by millions. That era saw also a boost in the production of educational multimedia CD-ROMs, the term video, if not used exclusively to describe motion photography, is ambiguous in multimedia terminology. Video is often used to describe the format, delivery format. Multiple forms of content are often not considered modern forms of presentation such as audio or video. Likewise, single forms of content with single methods of information processing are often called multimedia. Performing arts may also be considered multimedia considering that performers and props are multiple forms of content and media. Multimedia presentations may be viewed by person on stage, projected, transmitted, a broadcast may be a live or recorded multimedia presentation. Broadcasts and recordings can be analog or digital electronic media technology. Digital online multimedia may be downloaded or streamed, streaming multimedia may be live or on-demand
20.
Data compression
–
In signal processing, data compression, source coding, or bit-rate reduction involves encoding information using fewer bits than the original representation. Compression can be lossy or lossless. Lossless compression reduces bits by identifying and eliminating statistical redundancy, no information is lost in lossless compression. Lossy compression reduces bits by removing unnecessary or less important information, the process of reducing the size of a data file is referred to as data compression. In the context of data transmission, it is called coding in opposition to channel coding. Compression is useful because it reduces resources required to store and transmit data, computational resources are consumed in the compression process and, usually, in the reversal of the process. Data compression is subject to a space–time complexity trade-off, Lossless data compression algorithms usually exploit statistical redundancy to represent data without losing any information, so that the process is reversible. Lossless compression is possible because most real-world data exhibits statistical redundancy, for example, an image may have areas of color that do not change over several pixels, instead of coding red pixel, red pixel. The data may be encoded as 279 red pixels and this is a basic example of run-length encoding, there are many schemes to reduce file size by eliminating redundancy. The Lempel–Ziv compression methods are among the most popular algorithms for lossless storage, DEFLATE is a variation on LZ optimized for decompression speed and compression ratio, but compression can be slow. DEFLATE is used in PKZIP, Gzip, and PNG, LZW is used in GIF images. LZ methods use a table-based compression model where table entries are substituted for repeated strings of data, for most LZ methods, this table is generated dynamically from earlier data in the input. The table itself is often Huffman encoded, current LZ-based coding schemes that perform well are Brotli and LZX. LZX is used in Microsofts CAB format, the best modern lossless compressors use probabilistic models, such as prediction by partial matching. The Burrows–Wheeler transform can also be viewed as a form of statistical modelling. The basic task of grammar-based codes is constructing a context-free grammar deriving a single string, sequitur and Re-Pair are practical grammar compression algorithms for which software is publicly available. In a further refinement of the use of probabilistic modelling. Arithmetic coding is a more modern coding technique that uses the mathematical calculations of a machine to produce a string of encoded bits from a series of input data symbols
21.
International Organization for Standardization
–
The International Organization for Standardization is an international standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization promotes worldwide proprietary and it is headquartered in Geneva, Switzerland, and as of March 2017 works in 162 countries. It was one of the first organizations granted general consultative status with the United Nations Economic, ISO, the International Organization for Standardization, is an independent, non-governmental organization, the members of which are the standards organizations of the 162 member countries. It is the worlds largest developer of international standards and facilitates world trade by providing common standards between nations. Nearly twenty thousand standards have been set covering everything from manufactured products and technology to food safety, use of the standards aids in the creation of products and services that are safe, reliable and of good quality. The standards help businesses increase productivity while minimizing errors and waste, by enabling products from different markets to be directly compared, they facilitate companies in entering new markets and assist in the development of global trade on a fair basis. The standards also serve to safeguard consumers and the end-users of products and services, the three official languages of the ISO are English, French, and Russian. The name of the organization in French is Organisation internationale de normalisation, according to the ISO, as its name in different languages would have different abbreviations, the organization adopted ISO as its abbreviated name in reference to the Greek word isos. However, during the meetings of the new organization, this Greek word was not invoked. Both the name ISO and the logo are registered trademarks, the organization today known as ISO began in 1926 as the International Federation of the National Standardizing Associations. ISO is an organization whose members are recognized authorities on standards. Members meet annually at a General Assembly to discuss ISOs strategic objectives, the organization is coordinated by a Central Secretariat based in Geneva. A Council with a membership of 20 member bodies provides guidance and governance. The Technical Management Board is responsible for over 250 technical committees, ISO has formed joint committees with the International Electrotechnical Commission to develop standards and terminology in the areas of electrical and electronic related technologies. Information technology ISO/IEC Joint Technical Committee 1 was created in 1987 to evelop, maintain, ISO has three membership categories, Member bodies are national bodies considered the most representative standards body in each country. These are the members of ISO that have voting rights. Correspondent members are countries that do not have their own standards organization and these members are informed about ISOs work, but do not participate in standards promulgation. Subscriber members are countries with small economies and they pay reduced membership fees, but can follow the development of standards
22.
International Electrotechnical Commission
–
The IEC also manages three global conformity assessment systems that certify whether equipment, system or components conform to its International Standards. The first International Electrical Congress took place in 1881 at the International Exposition of Electricity, at that time the International System of Electrical and Magnetic Units was agreed to. The IEC was instrumental in developing and distributing standards for units of measurement, particularly Gauss, Hertz and it also first proposed a system of standards, the Giorgi System, which ultimately became the SI, or Système International d’unités. In 1938, it published a multilingual international vocabulary to unify terminology relating to electrical, electronic and this effort continues, and the International Electrotechnical Vocabulary remains an important work in the electrical and electronic industries. The CISPR – in English, the International Special Committee on Radio Interference – is one of the groups founded by the IEC, originally located in London, the commission moved to its current headquarters in Geneva in 1948. It has regional centres in Asia-Pacific, Latin America and North America, today, the IEC is the worlds leading international organization in its field, and its standards are adopted as national standards by its members. The work is done by some 10,000 electrical and electronics experts from industry, government, academia, test labs, IEC standards have numbers in the range 60000–79999 and their titles take a form such as IEC60417, Graphical symbols for use on equipment. Following the Dresden Agreement with CENELEC the numbers of older IEC standards were converted in 1997 by adding 60000, for example IEC27 became IEC60027. Standards of the 60000 series are also preceded by EN to indicate that the IEC standard is also adopted by CENELEC as a European standard. The IEC cooperates closely with the International Organization for Standardization and the International Telecommunication Union, Standards developed jointly with ISO such as ISO/IEC26300, ISO/IEC27001, and CASCO ISO/IEC17000 series, carry the acronym of both organizations. The use of the ISO/IEC prefix covers publications from ISO/IEC Joint Technical Committee 1 - Information Technology, as well as conformity assessment standards developed by ISO CASCO, other standards developed in cooperation between IEC and ISO are assigned numbers in the 80000 series, such as IEC 82045-1. IEC standards are also being adopted by other certifying bodies such as BSI, CSA, UL & ANSI/INCITS, SABS, SAI, SPC/GB, IEC standards adopted by other certifying bodies may have some noted differences from the original IEC standard. The IEC is made up of members, called national committees, national committees are constituted in different ways. Some NCs are public sector only, some are a combination of public and private sector, about 90% of those who prepare IEC standards work in industry
23.
MPEG-1
–
MPEG-1 is a standard for lossy compression of video and audio. Today, MPEG-1 has become the most widely compatible lossy audio/video format in the world, perhaps the best-known part of the MPEG-1 standard is the MP3 audio format it introduced. The MPEG-1 standard is published as ISO/IEC11172 – Information technology—Coding of moving pictures, MPEG was formed to address the need for standard video and audio formats, and to build on H.261 to get better quality through the use of more complex encoding methods. Development of the MPEG-1 standard began in May 1988, fourteen video and fourteen audio codec proposals were submitted by individual companies and institutions for evaluation. The codecs were extensively tested for computational complexity and subjective quality and this specific bitrate was chosen for transmission over T-1/E-1 lines and as the approximate data rate of audio CDs. The codecs that excelled in testing were utilized as the basis for the standard and refined further, with additional features. The reported completion date of the MPEG-1 standard varies greatly, a complete draft standard was produced in September 1990. The draft standard was publicly available for purchase, the standard was finished with the 6 November 1992 meeting. The Berkeley Plateau Multimedia Research Group developed an MPEG-1 decoder in November 1992, due in part to the similarity between the two codecs, the MPEG-2 standard includes full backwards compatibility with MPEG-1 video, so any MPEG-2 decoder can play MPEG-1 videos. This means that MPEG-1 coding efficiency can vary depending on the encoder used. The first three parts of ISO/IEC11172 were published in August 1993, the ISO patent database lists one patent for ISO11172, US4,472,747, which expired in 2003. The near-complete draft of the MPEG-1 standard was publicly available as ISO CD11172 by December 6,1991, a May 2009 discussion on the whatwg mailing list mentioned US5,214,678 patent as possibly covering MPEG audio layer II. Filed in 1990 and published in 1993, this patent is now expired, most popular software for video playback includes MPEG-1 decoding, in addition to any other supported formats. The popularity of MP3 audio has established a massive installed base of hardware that can play back MPEG-1 Audio, virtually all digital audio devices can play back MPEG-1 Audio. Many millions have been sold to-date, before MPEG-2 became widespread, many digital satellite/cable TV services used MPEG-1 exclusively. The widespread popularity of MPEG-2 with broadcasters means MPEG-1 is playable by most digital cable and satellite set-top boxes, MPEG-1 was used for full-screen video on Green Book CD-i, and on Video CD. The Super Video CD standard, based on VCD, uses MPEG-1 audio exclusively, the DVD-Video format uses MPEG-2 video primarily, but MPEG-1 support is explicitly defined in the standard. The DVD-Video standard originally required MPEG-1 Layer II audio for PAL countries, MPEG-1 Layer II audio is still allowed on DVDs, although newer extensions to the format, like MPEG Multichannel, are rarely supported
24.
MPEG-2
–
MPEG-2 is a standard for the generic coding of moving pictures and associated audio information. MPEG-2 is widely used as the format of television signals that are broadcast by terrestrial, cable. It also specifies the format of movies and other programs that are distributed on DVD, TV stations, TV receivers, DVD players, and other equipment are often designed to this standard. MPEG-2 was the second of several developed by the Moving Pictures Expert Group and is an international standard. Parts 1 and 2 of MPEG-2 were developed in a collaboration with ITU-T, while MPEG-2 is the core of most digital television and DVD formats, it does not completely specify them. Regional institutions can adapt it to their needs by restricting and augmenting aspects of the standard, MPEG-2 includes a Systems section, part 1, that defines two distinct, but related, container formats. Program stream exceptions are M2TS, which is used on Blu-ray discs, AVCHD on re-writable DVDs, while VOB on DVDs and Enhanced VOB on the short lived HD DVD do not waste storage space and just use the program stream. MPEG-2 Systems is formally known as ISO/IEC 13818-1 and as ITU-T Rec, ISO authorized the SMPTE Registration Authority, LLC as the registration authority for MPEG-2 format identifiers. This provision will permit the MPEG-2 transport standard to all types of data while providing for a method of unambiguous identification of the characteristics of the underlying private data. The Video section, part 2 of MPEG-2, is similar to the previous MPEG-1 standard, but also support for interlaced video. MPEG-2 video is not optimized for low bit-rates, especially less than 1 Mbit/s at standard definition resolutions, all standards-compliant MPEG-2 Video decoders are fully capable of playing back MPEG-1 Video streams conforming to the Constrained Parameters Bitstream syntax. MPEG-2/Video is formally known as ISO/IEC 13818-2 and as ITU-T Rec, with some enhancements, MPEG-2 Video and Systems are also used in some HDTV transmission systems, and is the standard format for over-the-air ATSC digital television.1 multichannel. This method is backwards-compatible, allowing MPEG-1 audio decoders to decode the two main components of the presentation. MPEG-2 part 3 also defined additional bit rates and sample rates for MPEG-1 Audio Layer I, MPEG-2 BC low bitrate encoding with halved sampling rate multichannel encoding with up to 5.1 channels, a. k. a. MPEG Multichannel Part 7 of the MPEG-2 standard specifies a rather different, Part 7 is referred to as MPEG-2 AAC. AAC is more efficient than the previous MPEG audio standards, and is in some ways less complicated than its predecessor, MPEG-1 Audio, Layer 3, in that it does not have the hybrid filter bank. It supports from 1 to 48 channels at sampling rates of 8 to 96 kHz, with multichannel, multilingual, advanced Audio is also defined in Part 3 of the MPEG-4 standard. MPEG-2 NBC MPEG-2 AAC multichannel encoding with up to 48 channels MPEG-2 standards are published as parts of ISO/IEC13818, each part covers a certain aspect of the whole specification
25.
H.262/MPEG-2 Part 2
–
H.262 or MPEG-2 Part 2 is a video coding format developed and maintained jointly by ITU-T Video Coding Experts Group and ISO/IEC Moving Picture Experts Group. It is the part of the ISO/IEC MPEG-2 standard. The ITU-T Recommendation H.262 and ISO/IEC 13818-2 documents are identical, the standard is available for a fee from the ITU-T and ISO. MPEG-2 Video is similar to MPEG-1, but also support for interlaced video. MPEG-2 video is not optimized for low bit-rates, but outperforms MPEG-1 at 3 Mbit/s, all standards-conforming MPEG-2 Video decoders are fully capable of playing back MPEG-1 Video streams. The ISO/IEC approval process was completed in November 1994, the first edition was approved in July 1995 and published by ITU-T and ISO/IEC in 1996. In 1996 it was extended by two amendments to include the Registration of Copyright Identifiers and the 4,2,2 Profile, ITU-T published these amendments in 1996 and ISO in 1997. There are also other amendments published later by ITU-T and ISO, the most recent edition of the standard was published in 2013 and incorporates all prior amendments. An HDTV camera generates a raw video stream of 149,299,200 bytes per second for 24fps video and this stream must be compressed if digital TV is to fit in the bandwidth of available TV channels and if movies are to fit on DVDs. Fortunately, video compression is practical because the data in pictures is often redundant in space, for example, the sky can be blue across the top of a picture and that blue sky can persist for frame after frame. Also, because of the way the eye works, it is possible to some data from video pictures with almost no noticeable degradation in image quality. TV cameras used in broadcasting usually generate 50 pictures a second or 59.94 pictures a second, digital television requires that these pictures be digitized so that they can be processed by computer hardware. Each picture element is represented by one luma number and two chrominance numbers. These describe the brightness and the color of the pixel, thus, each digitized picture is initially represented by three rectangular arrays of numbers. Upon reception/decoding, the two fields are displayed alternately with the lines of one field interleaving between the lines of the field, this format is called interlaced video. The typical field rate is 50 or 59.94 fields per second, if the video is not interlaced, then it is called progressive video and each picture is a frame. Another common practice to reduce the rate is to thin out or subsample the two chrominance planes. In effect, the chrominance values represent the nearby values that are deleted
