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					Audio/Video compression
An introduction


Alain Bouffioux
December, 20, 2006
Agenda
 Introduction - The evolution of Audio/Video consumer products and
 the role of compression techniques.
 Audio & Video compression principles
 Audio demonstration
 Video demonstration




                                                                                           2
                                        AV Compression / Alain Bouffioux   December, 20, 2006
Agenda
 Introduction - The evolution of Audio/Video consumer products
 and the role of compression techniques.
 Audio & Video compression principles
 Audio demonstration
 Video demonstration




                                                                                           3
                                        AV Compression / Alain Bouffioux   December, 20, 2006
Moore’s law

 Number of
 transistors per
 square inch
 doubles every 18
 months




                                                                       4
                    AV Compression / Alain Bouffioux   December, 20, 2006
Moore’s law today




 Cost of a transistor divided by one million in 30 years

                                                                                             5
                                          AV Compression / Alain Bouffioux   December, 20, 2006
Moore’s law today (2)                                          Itanium 2 (2004,
                                                               592,000,000)




 “Self-fulfulling prophecy”
 = roadmap for the semiconductor industry

                                                                                          6
                                       AV Compression / Alain Bouffioux   December, 20, 2006
Moore’s law today (3)
 Roadmap for semiconductor industry
 = only certainty in the current undefined future
 Progress in semiconductors
  = fuels the innovation
  = fuels the software revolution
  = fuels the wireless revolution
     (WLAN, WPAN, WBAN, …)
 Examples:
  WBAN & sensors, RFID applications, camera to swallow, flexible display…
 New products & related needs motivate semiconductor industry
 ( Self-fulfilling prophecy)
 Moore’s law will continue to apply: 10 years, 20 years ?
  – Economical limitation ? Investment (fixed) cost / globalisation
  – Power consumption (Moore’s low in reverse direction)
  – Architectural gap between IP-blocks & application (middleware still more
    complex…)


                                                                                              7
                                           AV Compression / Alain Bouffioux   December, 20, 2006
The evolution of CE products (1)
 Past: every CE product was analogue
 ~1983: Music becomes digital (CD players)
 Early 90ies: microprocessor enters CE devices
 (Early DVD players incorporated processing power equivalent to their
 comtemporary PC)
 Late 90ies: Communication features incorporated within a CE devices.
                    Computer                                    Consumer
                                       DVD                CD



                                             Receiver Digital TV or
                                             Residential gateway


                                                         Communication

                                                                                            8
                                         AV Compression / Alain Bouffioux   December, 20, 2006
The evolution of CE products (2)


 The Residential Gateway (Set-Top-Box, ADSL modem?) as the
 link between the home and the world-wide information
 infrastructure.



          World-wide
        communication     RG      Home Network
         infrastructure




                                                                                     9
                                  AV Compression / Alain Bouffioux   December, 20, 2006
The evolution of CE products (3)
    The Residential gateway (in home) as the gateway to various
    services.
    Local Server provides 2 kind of services:
       – Broadcast
         Analogue & digital TV, NVOD, PPV
       – Point-to-point (Home to local server)
         Home shopping, VOD, e-mail, Web browsing, PC connection...


                                                                         About 1000 homes
                                    Local server


             Network



                                      Internet




  Local server




                                                                                                     10
                                                 AV Compression / Alain Bouffioux     December, 20, 2006
The evolution of CE products (4)

 The Residential gateway as a key element of the home network
  To telephone Network

                                                        Computer

                     Residential
  To satellite        Gateway
  Network



  To cable Network
                                                                                Television
                                     Home Network




                            Disk                                     DVD
                          Recorder                                  Jukebox


                                                                                               11
                                             AV Compression / Alain Bouffioux   December, 20, 2006
The evolution of CE products (5)


 Everything will become digital: audio, telephone, video, photography,
 newspaper…
 The question is not if a selected product will really become digital; the
 question is when?
 Consumer/Computer/Communication Convergence is progressive
 New products combine all 3 domains
 (e.g. New GSM devices – Television on mobile)
 Products always more and more complex
 Products have always new features
 Lifetime of products is always shorter




                                                                                             12
                                           AV Compression / Alain Bouffioux   December, 20, 2006
Factors enabling such evolution
Compression is one among the various factors (all powered by
 semiconductor progresses) that enable multimedia technologies.

        Audio/Video                         Disc capacity (DVD), communication
        Compression                         going digital (xDSL, DVB, IP......)
        (e.g. CCIR601 vs MPEG)



                              Multimedia


    Electronics                                        International cooperation
    (Memory capacity,                                  (interoperability &
    clock frequency,         Software (methodology,    economy of scale)
    µP architecture, ...     user interface ...)
    --> decoding at low cost




                                                                                                   13
                                                 AV Compression / Alain Bouffioux   December, 20, 2006
BUT !!

 Convergence of technologies (consumer, communication, computer)
 All products combine all three technologies


 BUT !


 Divergence of applications
  – Home consumer, Multimedia phone, Camera, PDA, Office
    computer, Automotive…
  – High number of potential products
    Technology push Market pull (user centric approach)




                                                                                      14
                                    AV Compression / Alain Bouffioux   December, 20, 2006
Agenda
 Introduction - The evolution of Audio/Video consumer products and
 the role of compression techniques.
 Audio & Video compression principles
 Audio demonstration
 Video demonstration




                                                                                          15
                                        AV Compression / Alain Bouffioux   December, 20, 2006
Compression in first A/V CE Products (1)

 First Audio/Video products made compression without knowing it was
 compression.
 How ?
 By removal of irrelevancies (sampling rate, quantization)
 Audio and Video characteristics


                               Audio                            Video
          Spectral             Good                              Bad
         Sensitivity
           Spatial                 Bad                           Good
         Sensitivity


                                                                                           16
                                         AV Compression / Alain Bouffioux   December, 20, 2006
Compression in first A/V CE Products (2)

 Audio products
 From 2 to 7.1 channels are enough to provide the spatial resolution.
 Video products
 Three colours (RGB) are enough to provide the spectral resolution.




                                                                                          17
                                        AV Compression / Alain Bouffioux   December, 20, 2006
The need for more compression (1/5)
 Audio: Compression needed in spectral domain
 Bitrate of a stereo audio source (CD-DA encoding)
        i        f r ti
   A ud o w a ve o m (m e )




                                     ti
                                     me
 Sampling frequency : 44.1 kHz
 Stereo
 16-bit per sample
 Bitrate = 44100 * 2 * 16 = 1.41 Mbit/sec

                                                                                              18
                                            AV Compression / Alain Bouffioux   December, 20, 2006
The need for more compression (2/5)
 Video: Compression needed in spatial domain
 Bitrate of a video source (CCIR 601 - 50 Hz countries)
           i   i
         V deo m age
                             m l
                       720 sa p e s



         576
           i
          lne s




 25 images per second
 YUV coding (Y: luminance - U,V : Chrominance)
 Y: 8 bit per pixel - U,V: 1 pixel on 2 coded, 8 bit per pixel
 Bitrate = (576*720)*25*16 = 166 Mbit/sec

                                                                                            19
                                          AV Compression / Alain Bouffioux   December, 20, 2006
The need for more compression (3/5)
 Channels availables for AV transmission
  – Analog television channel (compatibility)
    Cable (bandwidth = 8 MHz)
    Satellite (Bandwidth = 30-40 MHz)

     Capacity around 40 Mbit/sec

  – Compact disc (CD)
    For 74 min. play time : 1.41 Mbit/sec




                                                                                        20
                                      AV Compression / Alain Bouffioux   December, 20, 2006
The need for more compression (4/5)
 MPEG-1 target (Moving Picture Expert Group)
 (Video-CD : 74 min. constraints)


       i             s
     V deo :166M b it/ e c
                                                   .      s
                                                 1 4M b it/ e c
          i    .      s
     A ud o :1 4M b it/ e c

                                 m e i
                              C o p r ss on

 But quality was judged too poor (about VHS quality)




                                                                                         21
                                       AV Compression / Alain Bouffioux   December, 20, 2006
The need for more compression (5/5)
 MPEG-2 target
  – Program stream (DVD)

           o a
     1 p r g rm
         i
      (v d e o ,                               9       s             i l      t
                                            3 - M b it/ e c (va ra b e b itra e )
             i
     m u ltch a n n e l                      b     i               y t            1
                                            ( u th g h e r q u a lit h a nM PEG - )
            i
     a u d o , ....)
                                                          i i f t                 y
                                                 = m o tva to n o r h e ca p a c it
                             m e i
                          C o p r ss on           i              t         >
                                                 n c re a se o f h e C D (-- D VD )


  – Transport stream (DVB)

                 m
     n p ro g ra s
         i
      (v d e o ,                                                               a            e
                                            a b o u t 4 0 M b it /se c (co n s t n t b itra t )
             i
     m u lt cha nne l                       (        S e e                -
                                            D V B - a t llit & D VB C a b e )    l
            i
     a ud o , . . . .)

                             m        i
                          C o p re ss o n


                                                                                                             22
                                                      AV Compression / Alain Bouffioux        December, 20, 2006
Principles of compression (1/2)
 Compression (or source coding) is achieved by suppressing
 information :
   – redundant information
   – irrelevant information
 Suppression of redundant information
  lossless compression
 example: PCM to DPCM,DCT
 The original signal and the one obtained after encoding and
 decoding are identical


F c (x ,y ,t)
                                                                           F p (x ,y ,t) = F c (x ,y ,t)
                              i
                C om p re s s o n                               i
                                               D e com p re s s o n
R c kb p s                          R i< R c                               Rp =R c

                                                                                                               23
                                                      AV Compression / Alain Bouffioux          December, 20, 2006
Principles of compression (2/2)
   Suppression of irrelevant information
    lossy compression
   Example: bandwidth limitation, masking in audio




   The original signal and the one obtained after encoding and
   decoding are different but are perceived as identical


F c (x ,y ,t)
                                                                            F p (x ,y ,t) <> F c (x ,y ,t)
                              i
                C om p re s s o n                               i
                                               D e com p re s s o n
R c kb p s                          R i< R c                                Rp =R c

                                                                                                              24
                                                      AV Compression / Alain Bouffioux         December, 20, 2006
Agenda
 Introduction - The evolution of Audio/Video consumer products and
 the role of compression techniques.
 Audio & Video compression principles
 Audio demonstration
 Video demonstration




                                                                                          25
                                        AV Compression / Alain Bouffioux   December, 20, 2006
Audio Demonstration
 From “Borderline” Madonna - Stereo - 16 bit/channel
 Compression used AAC


                  Original     705 kbps


         Compression
                                128            64             32         16
                                kbps           kbps           kbps       kbps
        Decompression


              -

                                                                                      26
                                    AV Compression / Alain Bouffioux   December, 20, 2006
MOS scale (1/2)

 Signal distortion is not a good measure of the performance of a lossy
 compression method
  an other method is necessary: MOS scale (Mean Opinion Score)
 The five-grade CCIR impairment scale (Rec.562)
 1(Very annoying), 2(Annoying), 3(Slightly annoying), 4(Perceptible but
 not annoying), 5(Imperceptible)
 Example:Double blind test




                                                                                          27
                                        AV Compression / Alain Bouffioux   December, 20, 2006
MOS scale (2/2)
                 i i     i
             O r g na ls g n a l          m e          i
                                       C o p r sse d s g na l


                                         E xcha n g e b o x
                                          (
                                         R a nd o     f     i t
                                                 m o r ls en e r )

                                              l t
                                         S e ec o r
                                                 o l         i t
                                          (co n tr le d b y ls e n e r )



                                             i t             w     t
                                           L s e n e r a n s e rs o :
                                             .      i      i     i t   i i
                                           1 W h ch s g n a l s he o r g na l? 2 o r 3 ?
                                             G a         t     t
                                           2 . r d e h e o he r on e ?



   5   I      r
              i
       m pa m en t
            l
       s ca e                                                                  Co    e
                                                                                 m p r s se d

                                                                                  i i
                                                                               O rg n a l

                                                                                        l
                                                                               M a x va u e
   4
                                                                                          l
                                                                               M e a n va u e

                                                                               M      i    l
                                                                                      n va u e


   3

               1                   2             3         S e q ue n ce




                                                                                                          28
                                                   AV Compression / Alain Bouffioux        December, 20, 2006
Agenda
 Introduction - The evolution of Audio/Video consumer products and
 the role of compression techniques.
 Audio & Video compression principles
 Audio demonstration
 Video demonstration




                                                                                          29
                                        AV Compression / Alain Bouffioux   December, 20, 2006
Compression to VBR or to CBR
     B it
      r e
      a t                            t
                              C on s an t
                                   a t
                              b it r e
                                                         t
                                               C on s an t
                                                        y
                                               q u a l it



                                                                  m  l
                                                               C o p ex

                                                                 i   l
                                                                Sm p e


                                                                     i t s i
                                                                   D s o r on


 CBR (Constant Bit Rate) vs VBR (Variable Bit Rate)
 Scene more complex Higher bit rate for same quality
 CBR  variable quality (example : Video CD artefact)
 Constant quality  VBR necessary (e.g.: DVD-Video)


                                                                                              30
                                            AV Compression / Alain Bouffioux   December, 20, 2006
Video demonstration

 MPEG-1 Example
 Video CD standard
 (288*352)video – CBR 1.4 Mbps
 MPEG-2 Example
 DVD standard
 (576*720)video – VBR ~3Mbps




                                                                                   31
                                 AV Compression / Alain Bouffioux   December, 20, 2006
The compression trade-off
 Compression techniques are still making progress
 Trade-off Complexity/Quality/Bit Rate
 New technique may result in new trade-off
                                    Complexity
 Quality


                                                                       MPEG Layer 2

                                                              MPEG Layer 1



                                                MPEG Layer 3
                       Other Technique
                       Speech coding            MPEG AAC


                                                                            Bitrate

                                                                                            32
                                         AV Compression / Alain Bouffioux    December, 20, 2006
                                                  33
AV Compression / Alain Bouffioux   December, 20, 2006

				
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