Multimedia 1 2(Song Ngu)

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Cng ngh MultimediaKhi qut Gii thiu Chng 1: Nn tng k thut nn Chng 2: Cc k thut multimediaJpeg Mpeg-1/Mpeg-2 Audio&Video Mpeg-4 Mpeg-7 (Gii thiu vn tt) HDTV (Gii thiu vn tt) H261/H263 (Gii thiu vn tt) Model-Based coding (Gii thiu vn tt)

Chng 3: Mng multimedia9/14/2006 Nguyen Chan Hung Hanoi University of Technology 1

Multimedia TechnologyOverviewIntroduction Chapter 1: Background of compression techniques Chapter 2: Multimedia technologiesJPEG MPEG-1/MPEG-2 Audio & Video MPEG-4 MPEG-7 (brief introduction) HDTV (brief introduction) H261/H263 (brief introduction) Model base coding (MBC) (brief introduction)

Chapter 3: Multimedia Network9/14/2006 Nguyen Chan Hung Hanoi University of Technology 2

Gii thiuTm quan trng ca cc k thut Multimedia: -> Multimedia c khp niTrong PC:Real player, Quicktime, Media m nhc, hnh nh min ph trn internet (mp2, mp3, mp4, asf, ra, ram, mid, DIVX, v..v...) Hi tho trc tuyn m thanh, hnh nh Dch v qung co trn web, truyn s liu Gio dc t xa. Y hc t xa ........

Trong truyn hnh v cc thit b in t dn dng:DVB-T/DVB-C/DVB-S (Digital Video Broadcastsing-Terrestrial/Cable/Satellite _ Truyn hnh s mt t/cp/v tinh) -> biu din MPEG-2 cht lng cao hn hn truyn hnh tng t truyn thng. Truyn hnh tng tc -> Cc ng dng internet trn truyn hnh (Mail,Web, Ecommerce_thng mi in t) -> khng cn i PC khi ng, tt my. Cc u c CD/VCD/DVD/Mp3

ng thi xut hin trn cc thit b cm tay ( TD th h 3G, PDA khng dy)

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IntroductionThe importance of Multimedia technologies: Multimedia everywhere !! On PCs: Real Player, QuickTime, Windows Media. Music and Video are free on the INTERNET (mp2, mp3, mp4, asf, mpeg, mov, ra, ram, mid, DIVX, etc) Video/Audio Conferences. Webcast/ Streaming Applications Distance Learning (or Tele-Education) Tele-Medicine Tele-xxx (Lets imagine !!) On TVs and other home electronic devices: DVB-T/DVB-C/DVB-S (Digital Video Broadcasting Terrestrial/Cable/Satellite) shows MPEG-2 superior quality over traditional analog TV !! Interactive TV Internet applications (Mail, Web, E-commerce) on a TV !! No need to wait for a PC to startup and shutdown !! CD/VCD/DVD/Mp3 players Also appearing in Handheld devices (3G Mobile phones, wireless PDA) !!9/14/2006 Nguyen Chan Hung Hanoi University of Technology 4

Gii thiu (2)Mng MultimediaInternet c thit k vo nhng nm 60 cho cc mng tc thp vi nhng ng dng vn bn nhm chn. -> tr cao, jitter cao. -> Nhng ng dng multimedia yu cu c s bin i mnh m ca c s h tng internet. Nhiu c cu t chc c nghin cu v trin khai h tr cho th h multimedia internet tip theo. (VD: intServ, DiffServ) Trong tng lai, tt c mi tivi (v PC) s kt ni internet v bt sng min ph vi hng triu trm pht sng trn ton th gii. Hin ti, mng multimedia chy trn ATM ( c), IPv4, v tng lai l IPv6 -> nn s bo m c cht lng dch v QoS (Quality of Service)9/14/2006 Nguyen Chan Hung Hanoi University of Technology 5

Introduction (2)Multimedia networkThe Internet was designed in the 60s for low-speed internetworks with boring textual applications High delay, high jitter. Multimedia applications require drastic modifications of the INTERNET infrastructure. Many frameworks have been being investigated and deployed to support the next generation multimedia Internet. (e.g. IntServ, DiffServ) In the future, all TVs (and PCs) will be connected to the Internet and freely tuned to any of millions broadcast stations all over the World. At present, multimedia networks run over ATM (almost obsolete), IPv4, and in the future IPv6 should guarantee QoS (Quality of Service) !!

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Chng 1: Nn tng k thut nnTi sao phi nn ?Trong truyn thng: thu hp di thng trong cc ng dng mng multimedia nh streaming, video theo yu cu VOD (video on demand), internet phone. Cc vt cha k thut s (VCD, DVD, bng v..v..) -> gim kch c, gim gi c, tng dung lng v cht lng ct gi m thanh, hnh nh.

H s nn hay t l nnT l gia d liu ngun v d liu nn (VD: 10:1)

2 loi nn:Nn khng tn hao Nn tn hao

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Chapter 1: Background of compression techniquesWhy compression ?For communication: reduce bandwidth in multimedia network applications such as Streaming media, Video-onDemand (VOD), Internet Phone Digital storage (VCD, DVD, tape, etc) Reduce size & cost, increase media capacity & quality.

Compression factor or compression ratioRatio between the source data and the compressed data. (e.g. 10:1)

2 types of compression:Lossless compression Lossy compression9/14/2006 Nguyen Chan Hung Hanoi University of Technology 8

2.1. Ni dung thng tin v d thaNi dung thng tin:Entropy l i lng o ca ni dung thng tin. Entropy quy nh gii hn di ca tc bit hay dng d liu.-> Biu din bi bits/n v ngun u ra (nh bits/pixel)

Tn hiu cng nhiu thng tin th entropy cng cao Nn tn hao th lm gim entropy cn nn khng tn hao th khng

D tha thng tin:L s khc nhau gia tc thng tin v tc bit Thng thng tc thng tin thp hn tc bit rt nhiu

Nn l loi b s d tha9/14/2006 Nguyen Chan Hung Hanoi University of Technology 9

Information content and redundancyInformation rate Entropy is the measure of information content.Expressed in bits/source output unit (such as bits/pixel).

The more information in the signal, the higher the entropy. Lossy compression reduce entropy while lossless compression does not. Redundancy The difference between the information rate and bit rate. Usually the information rate is much less than the bit rate. Compression is to eliminate the redundancy.9/14/2006 Nguyen Chan Hung Hanoi University of Technology 10

2.2. Entropy (B sung 1)For a discrete source X with a finite alphabet of N symbols (x0, . . ., xN.1) and a probability mass function of p(x), the entropy of the source in bits/symbol is given by

and measures the average number of bits/symbol required to describe the source. Such a discrete source is encountered in image compression, in which the acquired digital image pixels can take on only a finite number of values as determined by the number of bits used to represent each pixel. It is easy to show (using the method of Lagrange multipliers) that the uniform distribution achieves maximum entropy, given by H(X) = log2 N. A uniformly distributed source can be considered to have maximum randomness when compared with sources having other distributions Combining this with the intuitive English text example mentioned previously, it is apparent that entropy provides a measure of the compressibility of a source. High entropy indicates more randomness; hence the source requires more bits on average to describe a symbol.9/14/2006 Nguyen Chan Hung Hanoi University of Technology 11

Entropy (b sung 2)Calculating EntropyAn Example An example illustrates the computation of entropy the difficulty in determining the entropy of a fixed-length signal. Consider the four-point signal [3/4 1/4 0 0]. There are three distinct values (or symbols) in this signal, with probabilities 1/4, 1/4, and 1/2 for the symbols 3/4, 1/4, and 0, respectively. The entropy of the signal is then computed as

This indicates that a variable length code requires 1.5 bits/symbol on average to represent this source. In fact, a variable-length code that achieves this entropy is [10 11 0] for the symbols [3/4 1/4 0].

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2.3. Nn khng tn haoD liu gii m ging ht d liu ngunVD: Cc file u ra ca cc chng trnh tin ch nh pkzip hay Gzip H s nn khong 2:1 5:1 (ty theo d tha thng tin)

Khng th bo m 1 t l truyn c nh -> v tc d liu u ra bin i -> ny sinh cc vn cho c cu ghi v truyn thng.

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Lossless CompressionThe data from the decoder is identical to the source data.Example: archives resulting from utilities such as pkzip or Gzip Compression factor is around 2:1.

Can not guarantee a fix compression ratio The output data rate is variable problems for recoding mechanisms or communication channel.

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2.4. Nn tn hao:D liu gii nn khc dliu ngun nhng s khc bit khng th phn bit c r rng bng tai hoc mt thng.Ph hp vi m thanh, hnh nh nn. H s nn cao hn so vi nn khng tn hao (ln ti 100:1)

Da trn nhng kin thc v s nhn thc v th gic v thnh gic C thn nh 1 h s nn c nh9/14/2006 Nguyen Chan Hung Hanoi University of Technology 15

Lossy CompressionThe data from the expander is not identical to the source data but the difference can not be distinguished auditorily or visually.Suitable for audio and video compression. Compression factor is much higher than that of lossless. (up to 100:1)

Based on the understanding of psychoacoustic and psychovisual perception. Can be forced to operate at a fixed compression factor.9/14/2006 Nguyen Chan Hung Hanoi University of Technology 16

2.5. Qu trnh nn:Truyn thng (gim chi ph kt ni d liu)D liu -> B nn (m ho) -> knh truyn dn -> b gin (gii m) -> d liu

C cu ghi (tng thi gian pht li: t l vi h s nn)D liu -> nn (m ho) -> thit b cha (bng, a, Ram ...) -> b gin (gii m) -> D liu

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Process of CompressionCommunication (reduce the cost of the data link)DataCompressor (coder)transmission channel Expander (decoder) Data'

Recording (extend playing time: in proportion to compression factorData Compressor (coder) Storage device (tape, disk, RAM, etc.) Expander (decoder) Data

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2.6. Ly mu v