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aditya.s.hegde (1rv08cs009) Akhilesh kumar kc (1rv08cs010)

by. aditya.s.hegde (1rv08cs009) Akhilesh kumar kc (1rv08cs010). The Moving Picture Experts Group (MPEG) is a working group of ISO/IEC (formally ISO/IEC( International Electrotechnical Commission ) JTC1/SC29/WG11) in charge of

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aditya.s.hegde (1rv08cs009) Akhilesh kumar kc (1rv08cs010)

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  1. by aditya.s.hegde(1rv08cs009) Akhileshkumarkc(1rv08cs010)

  2. The Moving Picture Experts Group (MPEG) is a working group of ISO/IEC (formally ISO/IEC(International Electrotechnical Commission) JTC1/SC29/WG11) in charge of “development of international standards for compression, decompression, processing, and coded representation of moving pictures, audio, and their combination, in order to satisfy a wide variety of applications”. MPEG employs the term “generic standard” to convey this intention. • MPEG typically develops a standard through a sequence of steps: •  Identification of the need of a standard • Gathering of requirements • Call for proposals • Evaluation of proposals • Technical development MPEG

  3. . This makes it necessary to develop forms of audio-visual information representation that go beyond the simple waveform or sample-based, compression-based (such as MPEG-1 and MPEG-2) or even objects-based (such as MPEG-4) representations. • an image sensor may produce visual data not in the form of PCM samples (pixels values) but in the form of objects with associated physical measures and time information. • These could then be stored and processed to verify if certain programmed conditions are met. A PVR could receive descriptions of the audiovisual information associated to a program that would enable it to record, for example, only news with the exclusion of sport. Products from a company could be described in such a way that a machine could respond to unstructured queries from customers making inquiries. How is it important

  4. MPEG-3 is the designation for a group of audio and video coding standards agreed upon by the Moving Picture Experts Group (MPEG) designed to handle HDTV signals at 1080p in the range of 20 to 40 megabits per second.[ Mp3 is based on (Mpeg 1 audio layer 3) and(its not MPEG-3) Difference between Mpeg-3 and mp3

  5. MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to 1.5 Mbit/s (26:1 and 6:1 compression ratios respectively) [1] without excessive quality loss, making video CDs, digital cable/satellite TV and digital audio broadcasting (DAB) possible. MPEG-1 has become the most widely compatible lossy audio/video format in the world, and is used in a large number of products and technologies. Perhaps the best-known part of the MPEG-1 standard is the MP3 audio format it introduced. Filename extension .mpg, .mpeg, .mp1, .mp2, .mp3, .m1v, .m1a, .m2a, .mpa, .mpv Internet media type audio/mpeg, video/mpeg Developed by ISO, IEC Type of format audio, video, container Extended from JPEG, H.261 MPEG-1

  6. With some enhancements, MPEG-2 Video and Systems are also used in some HDTV transmission systems. • enhances MPEG-1's audio by allowing the coding of audio programs with more than two channels, up to 5.1 multichannel. This method is backwards-compatible(also known as MPEG-2 BC(the decoder)) • Video coding • An HDTV camera generates a raw video stream of 149,299,200 (=24*1920*1080*3)(142mbps) bytes per second for 24fps video. 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. • TV cameras used in broadcasting usually generate 25 pictures a second (in Europe) or 29.97 pictures a second (in North America MPEG-2

  7. Audio encoding MPEG-2 BC (backward compatible with MPEG-1 audio formats) low bitrate encoding with halved sampling rate (MPEG-1 Layer 1/2/3 LSF) multichannel encoding with up to 5.1 channels MPEG-2 NBC (Non-Backward Compatible) MPEG-2 AAC AAC is able to include 48 full-bandwidth (up to 96 kHz) audio channels in one stream plus 16 low frequency effects (LFE, limited to 120 Hz) channels, up to 16 "coupling" or dialog channels, and up to 16 data streams. AAC is also the default or standard audio format for: Apple's iPhone, iPod, iPad, Nintendo DSi, iTunes, DivX Plus Web Player, Sony's PlayStation 3 and is supported by Sony's PlayStation Portable, latest generation of Sony Walkman, phones from Sony Ericsson, the latest S40 and S60 models from Nokia, Android based phones, Nintendo's Wii (with the Photo Channel 1.1 update installed for Wii consoles purchased before late 2007), and the MPEG-4 video standard.

  8. AAC is a wideband audio coding algorithm that exploits two primary coding strategies to dramatically reduce the amount of data needed to represent high-quality digital audio. • Signal components that are perceptually irrelevant are discarded; • Redundancies in the coded audio signal are eliminated. • The actual encoding process consists of the following steps: • The signal is converted from time-domain to frequency-domain using forward modified discrete cosine transform (MDCT). This is done by using filter banks that take an appropriate number of time samples and convert them to frequency samples. • The frequency domain signal is quantized based on a psychoacoustic model and encoded. • Internal error correction codes are added; • The signal is stored or transmitted. • In order to prevent corrupt samples, a modern implementation of the Luhn mod N algorithm is applied to each frame Audio compression in mpeg-2

  9. Types of pictures • I (intra) frame • compressed using only intraframe coding • Moderate compression but faster random access • P (predicted) frame • Coded with motion compression using past I frames or P frames • Can be used as reference pictures for additional motion compensation • B (bidirectional) frame • Coded by motion compensation by either past or future I or P frames • D (DC) frame • Limited use: encodes only DC components of intraframe coding Basics of MPEG video coding

  10. MPEG and related codec employ a more complex frame-referencing method • intrapictures (I pictures) • predicted pictures (P pictures) • bidirectional pictures (B pictures) Temporal Video Compression

  11. An I-frame is a compressed version of a single uncompressed (raw) frame. • 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. • 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. 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 colour. • 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. Temporal Video Compression

  12. 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. • 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. Temporal Video Compression

  13. Temporal Video Compression • P-frames provide more compression than I-frames because they take advantage of the data in a previous I-frame or P-frame - a reference frame. • 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. 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.

  14. Temporal Video Compression • The match between the two macroblocks will often not be perfect. To correct for this, the encoder takes the difference of all corresponding pixels of the two macroblocks, and on that macroblock difference then computes the strings of coefficient values as described above. • 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 a subsequent reference frame as well as the picture in a preceding reference frame. • As a result, B-frames usually provide more compression than P-frames. B-frames are never reference frames.

  15. Adds new features such as (extended) VRML support for 3D rendering,. object-oriented composite files (including audio, video and VRML objects), support for externally-specified Digital Rights Management and various types of interactivity. AAC (Advanced Audio Coding) was standardized as an adjunct to MPEG-2 (as Part 7) before MPEG-4 was issued. AAC is more efficient than the previous MPEG audio standards. 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, and multiprogramming capabilities. MPEG-4 is efficient across a variety of bit-rates ranging from a few kilobits per second to tens of megabits per second. MPEG-4 provides the following functionalities: Improved coding efficiency over MPEG-2 Ability to encode mixed media data (video, audio, speech) Error resilience to enable robust transmission Ability to interact with the audio-visual scene generated at the receiver MPEG-4

  16. MPEG-7 is formally called Multimedia Content Description Interface. Thus, it is not a standard which deals with the actual encoding of moving pictures and audio, like MPEG-1, MPEG-2 and MPEG-4. • It uses XML to store metadata, and can be attached to timecode in order to tag particular events, or synchroniselyrics to a song, for example. Mpeg -7

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