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Not to be confused with MPEG-1 Audio Layer II (MP2). MPEG-1 Audio Layer II ( MP2, sometimes incorrectly called Musicam) is an Audio codec defined by ISO/IEC 11172-3
MPEG-2 is used in Digital Video Broadcast and Digital Versatile Discs. The transport stream, TS, and program stream, PS, are container formats.
MPEG-2 is used in Digital Video Broadcast and Digital Versatile Discs. The transport stream, TS, and program stream, PS, are container formats. Transport stream ( TS, TP, MPEG-TS, or M2T) is a Communications protocol for audio, video, and data Program stream ( PS or MPEG-PS) is a container format for multiplexing Digital audio, Video and more A container format is a computer file format that can contain various types of data compressed by means of standardized audio/video codecs.

MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". [1] It describes a combination of lossy video compression and lossy audio compression (audio data compression) methods which permit storage and transmission of movies using currently available storage media and transmission bandwidth. A lossy compression method is one where compressing data and then decompressing it retrieves data that may well be different from the original but is close enough to be useful Video compression refers to reducing the quantity of Data used to represent video images and is a straightforward combination of Image compression and Motion For processes which reduce the amount of time it takes to listen to and understand a recording see Time-compressed speech.

Contents

Main characteristics

MPEG-2 is widely used as the format of digital television signals that are broadcast by terrestrial (over-the-air), cable, and direct broadcast satellite TV systems. Terrestrial television is a term which refers to modes of television broadcasting which do not involve satellite transmission Direct broadcast satellite (DBS is a term used to refer to Satellite television broadcasts intended for home reception also referred to more broadly as direct-to-home Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic It also specifies the format of movies and other programs that are distributed on DVD and similar disks. DVD (also known as " Digital Versatile Disc " or " Digital Video Disc " - see Etymology)is As such, TV stations, TV receivers, DVD players, and other equipment are often designed to this standard. MPEG-2 was the second of several standards developed by the Moving Pictures Expert Group (MPEG) and is an international standard (ISO/IEC 13818). The Moving Picture Experts Group, commonly referred to as simply MPEG, is a Working group of ISO / IEC charged with the development of video and The International Electrotechnical Commission ( IEC) is a not-for-profit, non-governmental international Standards organization that prepares and publishes Parts 1 and 2 of MPEG-2 were developed in a joint collaborative team with ITU-T, and they have a respective catalog number in the ITU-T Recommendation Series. The ITU Telecommunication Standardization Sector ( ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication

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. See Profiles and Levels.

MPEG-2 includes a Systems section, part 1, that defines two distinct, but related, container formats. One is the Transport Stream, designed to carry digital video and audio over possibly lossy media, such as broadcasting, examples of which include ATSC and DVB. Transport stream ( TS, TP, MPEG-TS, or M2T) is a Communications protocol for audio, video, and data For the chemical compound see Divinylbenzene. Digital Video Broadcasting ( DVB) is a suite of internationally accepted MPEG-2 Systems also defines Program Stream, a container format designed for reasonably reliable media such as optical disks, DVDs and SVCDs. Program stream ( PS or MPEG-PS) is a container format for multiplexing Digital audio, Video and more DVD (also known as " Digital Versatile Disc " or " Digital Video Disc " - see Etymology)is Super Video CD ( Super Video Compact Disc or SVCD) is a Digital format for storing Video on standard Compact discs SVCD was intended MPEG-2/System is formally known as ISO/IEC 13818-1 and as ITU-T Rec. H. 222. 0. [2]

The Video section, part 2 of MPEG-2, is similar to the previous MPEG-1 standard, but also provides support for interlaced video, the format used by analog broadcast TV systems. MPEG-1 was an early Standard for Lossy compression of Video and audio. For the method of incrementally displaying Raster graphics, see Interlace (bitmaps. MPEG-2 video is not optimized for low bit-rates, especially less than 1 Mbit/s at standard definition resolutions. In Telecommunications and Computing, bitrate (sometimes written bit rate, data rate or as a Variable R or f b However, it outperforms MPEG-1 at 3 Mbit/s and above. All standards-compliant MPEG-2 Video decoders are fully capable of playing back MPEG-1 Video streams. MPEG-2/Video is formally known as ISO/IEC 13818-2 and as ITU-T Rec. H.262. H262 is an ITU-T Digital video coding standard It falls under the purview of the ITU-T Video Coding Experts Group (VCEG and is maintained jointly with [3]

With some enhancements, MPEG-2 Video and Systems are also used in some HDTV transmission systems. High-definition television (HDTV is a Digital television Broadcasting system with higher resolution than traditional television systems (standard-definition

The MPEG-2 Audio section, defined in part 3 of the standard, enhances MPEG-1's audio by allowing the coding of audio programs with more than two channels. 51, Multichannel audio, Multichannel music Surround 3D Surround 5 This method is backwards-compatible, allowing MPEG-1 audio decoders to decode the two main stereo components of the presentation.

Part 7 of the MPEG-2 standard specifies a rather different, non-backwards-compatible audio format. Part 7 is referred to as MPEG-2 AAC. Advanced Audio Coding ( AAC) is a standardized lossy compression and encoding scheme for Digital audio. While AAC is more efficient than the previous MPEG audio standards, it is much more complex to implement and somewhat more powerful hardware is needed for encoding and decoding. Advanced Audio Coding ( AAC) is a standardized lossy compression and encoding scheme for Digital audio. Advanced Audio is also defined in Part 3 of the MPEG-4 standard. MPEG-4 is a collection of methods defining compression of audio and visual (AV digital data

History


Video coding (simplified)

Main article: Video compression

An HDTV camera generates a raw video stream of up to 233,280,000 bytes per second. Video compression refers to reducing the quantity of Data used to represent video images and is a straightforward combination of Image compression and Motion High-definition television (HDTV is a Digital television Broadcasting system with higher resolution than traditional television systems (standard-definition 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 and time. Video compression refers to reducing the quantity of Data used to represent video images and is a straightforward combination of Image compression and Motion 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 delete some data from video pictures with almost no noticeable degradation in image quality.

TV cameras used in broadcasting usually generate 50 pictures a second (in Europe) or 59.94 pictures a second (in North America). PAL, short for Phase Alternating Line, is a colour -encoding system used in Broadcast television systems in large parts of the world NTSC ( National Television System Committee) is the Analog television system used in the United States, Canada, Japan, Mexico Digital television requires that these pictures be digitized so that they can be processed by computer hardware. Each picture element (a pixel) is then represented by one luma number and two chrominance numbers. In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image As applied to video signals luma represents the brightness in an image (the "black and white" or achromatic portion of the image Chrominance ( chroma for short is the signal used in many Video systems to carry the color information of the picture separately from the accompanying luma These describe the brightness and the color of the pixel (see YCbCr). YCbCr or Y'CbCr is a family of Color spaces used as a part of the Color image pipeline in Video and Digital photography systems Thus, each digitized picture is initially represented by three rectangular arrays of numbers.

A common (and old) trick to reduce the amount of data is to separate the picture into two fields: the "top field," which is the odd numbered rows, and the "bottom field," which is the even numbered rows. The two fields are displayed alternately. This is called interlaced video. For the method of incrementally displaying Raster graphics, see Interlace (bitmaps. Two successive fields are called a frame. The typical frame rate is then 25 or 29. 97 frames per second. If the video is not interlaced, then it is called progressive video and each picture is a frame. Progressive or noninterlaced scanning is a method for displaying storing or transmitting Moving images in which all the lines of each frame are drawn in MPEG-2 supports both options.

Another trick to reduce the data rate is to thin out the two chrominance matrices. Chroma subsampling is the practice of encoding images by implementing less resolution for chroma Information than for luma information In effect, the remaining chrominance values represent the nearby values that are deleted. Thinning works because the eye is more responsive to brightness than to color. The 4:2:2 chrominance format indicates that half the chrominance values have been deleted. Chroma subsampling is the practice of encoding images by implementing less resolution for chroma Information than for luma information The 4:2:0 chrominance format indicates that three quarters of the chrominance values have been deleted. If no chrominance values have been deleted, the chrominance format is 4:4:4. MPEG-2 allows all three options.

MPEG-2 specifies that the raw frames be compressed into three kinds of frames: intra-coded frames (I-Frame), predictive-coded frames (P-frames), and bidirectionally-predictive-coded frames (B-frames). I-frame redirects here For the HTML-element see IFrame. The three major picture types found in typical Video compression designs are I-frame redirects here For the HTML-element see IFrame. The three major picture types found in typical Video compression designs are I-frame redirects here For the HTML-element see IFrame. The three major picture types found in typical Video compression designs are

An I-Frame is a compressed version of a single uncompressed (raw) frame. I-frame redirects here For the HTML-element see IFrame. The three major picture types found in typical Video compression designs are It takes advantage of spatial redundancy and of the inability of the eye to detect certain changes in the image. Unlike P-frames and B-frames, I-frames do not depend on data in the preceding or the following frames. Briefly, the raw frame is divided into 8 pixel by 8 pixel blocks. The data in each block is transformed by a discrete cosine transform. A discrete cosine transform ( DCT) expresses a sequence of finitely many data points in terms of a sum of Cosine functions oscillating at different frequencies The result is an 8 by 8 matrix of coefficients. The transform converts spatial variations into frequency variations, but it does not change the information in the block; the original block can be recreated exactly by applying the inverse cosine transform. The advantage of doing this is that the image can now be simplified by quantizing the coefficients. Quantization, involved in Image processing, is a Lossy compression technique achieved by compressing a range of values to a single quantum value Many of the coefficients, usually the higher frequency components, will then be zero. The penalty of this step is the loss of some subtle distinctions in brightness and color. If one applies the inverse transform to the matrix after it is quantized, one gets an image that looks very similar to the original image but that is not quite as nuanced. Next, the quantized coefficient matrix is itself compressed. Typically, one corner of the quantized matrix is filled with zeros. By starting in the opposite corner of the matrix, then zigzagging through the matrix to combine the coefficients into a string, then substituting run-length codes for consecutive zeros in that string, and then applying Huffman coding to that result, one reduces the matrix to a smaller array of numbers. Run-length encoding ( RLE) is a very simple form of Data compression in which runs of data (that is sequences in which the same data value occurs in many History In 1951 David A Huffman and his MIT information theory classmates were given It is this array that is broadcast or that is put on DVDs. In the receiver or the player, the whole process is reversed, enabling the receiver to reconstruct, to a close approximation, the original frame.

Typically, every 15th frame or so is made into an I-frame. P-frames and B-frames might follow an I-frame like this, IBBPBBPBBPBB(I), to form a Group Of Pictures (GOP); however, the standard is flexible about this. In MPEG encoding, a group of pictures, or GOP, specifies the order in which Intra-frames and Inter frames are arranged

Macroblocks

P-frames provide more compression than I-frames because they take advantage of the data in the previous I-frame or P-frame. I-frames and P-frames are called reference frames. Reference frames are frames of a compressed video that are used to define future frames To generate a P-frame, the previous reference frame is reconstructed, just as it would be in a TV receiver or DVD player. The frame being compressed is divided into 16 pixel by 16 pixel macroblocks. Macroblock is a term used in Video compression, which represents a block of 16 by 16 Pixels. Then, for each of those macroblocks, the reconstructed reference frame is searched to find that 16 by 16 macroblock that best matches the macroblock being compressed. The offset is encoded as a "motion vector. " Frequently, the offset is zero. But, if something in the picture is moving, the offset might be something like 23 pixels to the right and 4 pixels up. The match between the two macroblocks will often not be perfect. To correct for this, the encoder computes the strings of coefficient values as described above for both macroblocks and, then, subtracts one from the other. This "residual" is appended to the motion vector and the result sent to the receiver or stored on the DVD for each macroblock being compressed. Sometimes no suitable match is found. Then, the macroblock is treated like an I-frame macroblock.

The processing of B-frames is similar to that of P-frames except that B-frames use the picture in the following reference frame as well as the picture in the preceding reference frame. As a result, B-frames usually provide more compression than P-frames. B-frames are never reference frames.

While the above generally describes MPEG-2 video compression, there are many details that are not discussed including details involving fields, chrominance formats, responses to scene changes, special codes that label the parts of the bitstream, and other pieces of information.

Audio encoding

MPEG-2 also introduces new audio encoding methods. These are

Video profiles and levels

MPEG-2 video supports wide range of applications from mobile to high quality HD editing. Advanced Audio Coding ( AAC) is a standardized lossy compression and encoding scheme for Digital audio. For many applications, it's unrealistic and too expensive to support the entire standard. To allow such applications to support only subsets of it, the standard defines profile and level.

The profile defines the subset of features such as compression algorithm, chroma format, etc. The level defines the subset of quantitative capabilities such as maximum bit rate, maximum frame size, etc.

A MPEG application then specifies the capabilities in terms of profile and level. For example, a DVD player may say it supports up to main profile and main level (often written as MP@ML). It means the player can play back any MPEG stream encoded as MP@ML or less.

The tables below summarizes the limitations of each profile and level. There are many other constraints not listed here.

MPEG-2 Profiles
Abbr. Name Picture Coding Types Chroma Format Aspect Ratios Scalable modes
SP Simple profile I, P 4:2:0 square pixels, 4:3, or 16:9 none
MP Main profile I, P, B 4:2:0 square pixels, 4:3, or 16:9 none
SNR SNR Scalable profile I, P, B 4:2:0 square pixels, 4:3, or 16:9 SNR (signal-to-noise ratio) scalable
Spatial Spatially Scalable profile I, P, B 4:2:0 square pixels, 4:3, or 16:9 SNR- or spatial-scalable
HP High profile I, P, B 4:2:2 or 4:2:0 square pixels, 4:3, or 16:9 SNR- or spatial-scalable

Exempting scalability (a rarely used feature where one MPEG-2 stream augments another), the following are some of the constraints on levels:

MPEG-2 Levels
Abbr. Name Frame rates (Hz) Max horizontal resolution Max vertical resolution Max luminance samples per second (approximately height x width x framerate) Max bit rate in Main profile (Mbit/s)
LL Low Level 23. 976, 24, 25, 29. 97, 30 352 288 3,041,280 4
ML Main Level 23. 976, 24, 25, 29. 97, 30 720 576 10,368,000, except in High profile, where constraint is 14,475,600 for 4:2:0 and 11,059,200 for 4:2:2 15
H-14 High 1440 23. 976, 24, 25, 29. 97, 30, 50, 59. 94, 60 1440 1152 47,001,600, except that in High profile with 4:2:0, constraint is 62,668,800 60
HL High Level 23. 976, 24, 25, 29. 97, 30, 50, 59. 94, 60 1920 1152 62,668,800, except that in High profile with 4:2:0, constraint is 83,558,400 80

Applications

DVD

The DVD standard uses MPEG-2 video, but imposes some restrictions:

Note: By using a pattern of REPEAT_FIRST_FIELD flags on the headers of encoded pictures, pictures can be displayed for either two or three fields and almost any picture display rate (minimum ⅔ of the frame rate) can be achieved. This is most often used to display 23. 976 (approximately film rate) video on NTSC.

DVB

Application-specific restrictions on MPEG-2 video in the DVB standard:

Allowed resolutions for SDTV:

For HDTV:

ATSC and ISDB-T

Main article: ATSC Standards

The ATSC A/53 standard, used in the United States, uses MPEG-2 video at the Main Profile @ High Level, with additional restrictions:

Allowed video resolutions, aspect ratios, and frame/field rates:

Note that although the ATSC A/53 standard limits transmission to these 18 formats (and their 1000/1001-rate slowed-down versions), the U. S. Federal Communications Commission declined to mandate that television stations obey this part of the ATSC's standard. In theory, television stations in the U. S. are free to choose any resolution, aspect ratio, and frame/field rate, within the limits of Main Profile @ High Level. Many stations do go outside the bounds of the ATSC specification by using other resolutions – for example, 720 × 480.

Also note that the ATSC specification and MPEG-2 allow the use of progressive frames, even within an interlaced video sequence. For example, NBC stations transmit a 1080i30 video sequence – meaning the formal output of the MPEG-2 decoding process is sixty 540-line fields per second. But for prime-time television shows, those 60 fields can be coded with 24 progressive frames. Some NBC stations do this, meaning they actually transmit an 1080p24 video stream (a sequence of 24 progressive frames per second) with metadata instructing the decoder to interlace them (and repeat them in 3:2 pulldown) before display.

Thus, it would be incorrect to say that the ATSC standard doesn't contain 1080p video, or that broadcast HDTV doesn't use 1080p video. The ATSC specification allows 1080p30 and 1080p24 sequences – just not 1080p60 sequences. They aren't used in practice, because broadcasters want to be able to switch between 60 Hz (news, soap operas) and 24 Hz (prime-time) content without ending the MPEG-2 sequence. However, the ATSC specification also allows broadcasters to transmit progressive frames within an interlaced sequence, and some broadcasters actually do this in practice. Their transmissions could fairly be described as 1080p24, since they contain 24 progressively-coded frames per second. (This is the same mechanism used by HD-DVD to code 1080p24 content – progressive frames within an interlaced sequence. )

Note: The 1080-line formats are encoded with 1920 × 1088 pixel luma matrices and 960 × 540 chroma matrices, but the last 8 lines are discarded by the MPEG-2 decoding and display process.

MPEG-2 audio was a contender for the ATSC standard during the DTV "Grand Alliance" shootout, but lost out to Dolby AC-3. Digital television (DTV is the sending and receiving of moving images and sound by discrete ( digital) signals in contrast to the analog signals used by The Grand Alliance (GA was a Consortium created in 1993 at the behest of the Federal Communications Commission (FCC to develop the American HDTV specification Dolby Digital is the marketing name for a series of lossy audio compression technologies developed by Dolby

Note: All the text about Mpeg2 in ATSC is also valid for ISDB-T, except that in the main TS is aggregated a second program for mobile devices compressed in Mpeg-4 H. 264 AVC for video and AAC-LC for audio, mainly known as 1Seg.

ISO/IEC 13818

Part 1
Systems – describes synchronization and multiplexing of video and audio. Also known as ITU-T Rec. H. 222. 0. [2] See MPEG transport stream. Transport stream ( TS, TP, MPEG-TS, or M2T) is a Communications protocol for audio, video, and data
Part 2
Video – compression codec for interlaced and non-interlaced video signals. Also known as ITU-T Rec. H.262. H262 is an ITU-T Digital video coding standard It falls under the purview of the ITU-T Video Coding Experts Group (VCEG and is maintained jointly with
Part 3
Audio – compression codec for perceptual coding of audio signals. A multichannel-enabled extension of MPEG-1 audio.
Part 4
Describes procedures for testing compliance.
Part 5
Describes systems for Software simulation.
Part 6
Describes extensions for DSM-CC (Digital Storage Media Command and Control). Digital storage media command and control ( DSM-CC) is a toolkit for developing control channels associated with MPEG-1 and MPEG-2 streams
Part 7
Advanced Audio Coding (AAC). Advanced Audio Coding ( AAC) is a standardized lossy compression and encoding scheme for Digital audio.
Part 9
Extension for real time interfaces.
Part 10
Conformance extensions for DSM-CC.

(Part 8: 10-bit video extension. Primary application was studio video. Part 8 has been withdrawn due to lack of interest by industry. )

Patent holders

Approximately 640 patents worldwide make up the "essential" patents surrounding MPEG-2. A patent is a set of Exclusive rights granted by a State to an inventor or his assignee for a fixed period of time in exchange for a disclosure of an [4][5] These are held by over 20 corporations and one university. Where software patentability is upheld, the use of MPEG-2 requires the payment of licensing fees to the patent holders via the MPEG Licensing Association. Software patent does not have a universally accepted definition The patent pool is managed and administered by MPEG Licensing Authority, a private organization. In Patent law, a patent pool is a Consortium of at least two Companies agreeing to cross-license patents relating to a particular Technology MPEG LA LLC, is a firm which licenses Patent pools required for use of the MPEG-2, MPEG-4 Visual (Part 2 IEEE 1394, VC-1 Other patents are licensed by Audio MPEG, Inc. [6] The development of the standard itself took less time than the patent negotiations. [7][8]

MPEG-LA Patents

Non-MPEG-LA Patents

According to the MPEG-LA Licensing Agreement MPEG-LA, any use of MPEG-2 technology is subject to royalties. MPEG LA LLC, is a firm which licenses Patent pools required for use of the MPEG-2, MPEG-4 Visual (Part 2 IEEE 1394, VC-1 Royalties (sometimes running royalties) are usage-based payments made by one party (the "licensee" to another (the "licensor" for ongoing use of an

In the case of free software such as VLC media player (which uses the ffmpeg library) and in which the software is not sold, the end-user bears the royalty. Free software or software libre is Software that can be used studied and modified without restriction and which can be copied and redistributed in modified or unmodified FFmpeg is a computer program that can record convert and stream digital audio and Video in numerous formats

See also

References

  1. ^ ISO/IEC 13818 MPEG-2 at the ISO Store.
  2. ^ a b ITU-T Rec. H.222.0
  3. ^ ITU-T Rec. H.262
  4. ^ Mpeg La
  5. ^ audioMPEG.com - - - US Patents
  6. ^ audioMPEG.com - - - patent management and licensing company specializing in the licensing of audio technology
  7. ^ Richard M Stallman, Patents - Barriers to development Theora Video and Vorbis Audio
  8. ^ http://www.mpegla.com/m2/m2-att1.pdf
  9. ^ a b MPEG-2 PATENT PORTFOLIO LICENSE

External links

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