Audio/Video compression An introduction

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Audio/Video compressionAn introduction

• Alain Bouffioux
• December, 20, 2006

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Agenda

• Introduction - The evolution of Audio/Video
  consumer products and the role of compression
  techniques.
• Audio Video compression principles
• Audio demonstration
• Video demonstration

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Agenda

• Introduction - The evolution of Audio/Video
  consumer products and the role of compression
  techniques.
• Audio Video compression principles
• Audio demonstration
• Video demonstration

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Moores law

• Number of transistors per square inch doubles
  every 18 months

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Moores law today

• Cost of a transistor divided by one million in
  30 years

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Moores law today (2)
Itanium 2 (2004, 592,000,000)

• Self-fulfulling prophecy roadmap for the
  semiconductor industry

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Moores 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)
• Moores law will continue to apply 10 years, 20
  years ?
• Economical limitation ? Investment (fixed) cost
  / globalisation
• Power consumption (Moores low in reverse
  direction)
• Architectural gap between IP-blocks application
  (middleware still more complex)

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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.

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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.

Home Network
World-wide communication infrastructure
RG
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The evolution of CE products (3)

• The Residential gateway (in home) as the gateway
  to various services. Local Server provides 2
  kind of services
• BroadcastAnalogue 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
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The evolution of CE products (4)

• The Residential gateway as a key element of the
  home network

To telephone Network
Computer
Residential Gateway
To satellite Network
Home Network
Television
To cable Network
Disk Recorder
DVD Jukebox
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The evolution of CE products (5)

• Everything will become digital audio, telephone,
  video, photography, newspaperThe 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

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Factors enabling such evolution

• Compression is one among the various factors (all
  powered by semiconductor progresses) that enable
  multimedia technologies.

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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 productsTechnology push
  ?Market pull (user centric approach)

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Agenda

• Introduction - The evolution of Audio/Video
  consumer products and the role of compression
  techniques.
• Audio Video compression principles
• Audio demonstration
• Video demonstration

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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

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Compression in first A/V CE Products (2)

• Audio productsFrom 2 to 7.1 channels are enough
  to provide the spatial resolution.
• Video productsThree colours (RGB) are enough to
  provide the spectral resolution.

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The need for more compression (1/5)

• Audio Compression needed in spectral domain
• Bitrate of a stereo audio source (CD-DA
  encoding) Sampling frequency
  44.1 kHzStereo16-bit per sampleBitrate 44100
  2 16 1.41 Mbit/sec

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The need for more compression (2/5)

• Video Compression needed in spatial domain
• Bitrate of a video source (CCIR 601 - 50 Hz
  countries) 25 images per secondYUV
  coding (Y luminance - U,V Chrominance)Y 8
  bit per pixel - U,V 1 pixel on 2 coded, 8 bit
  per pixelBitrate (576720)2516 166 Mbit/sec

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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

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The need for more compression (4/5)

• MPEG-1 target (Moving Picture Expert
  Group)(Video-CD 74 min. constraints)Bu
  t quality was judged too poor (about VHS quality)

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The need for more compression (5/5)

• MPEG-2 target
• Program stream (DVD)
• Transport stream (DVB)

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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,DCTThe
  original signal and the one obtained after
  encoding and decoding are identical

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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

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Agenda

• Introduction - The evolution of Audio/Video
  consumer products and the role of compression
  techniques.
• Audio Video compression principles
• Audio demonstration
• Video demonstration

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Audio Demonstration

• From Borderline Madonna - Stereo - 16
  bit/channel
• Compression used AAC

Original
705 kbps
Compression
32 kbps
128 kbps
64 kbps
16 kbps
Decompression
-
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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)
• ExampleDouble blind test

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MOS scale (2/2)
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Agenda

• Introduction - The evolution of Audio/Video
  consumer products and the role of compression
  techniques.
• Audio Video compression principles
• Audio demonstration
• Video demonstration

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Compression to VBR or to CBR

• 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)

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Video demonstration

• MPEG-1 Example Video CD standard(288352)video
  CBR 1.4 Mbps
• MPEG-2 ExampleDVD standard(576720)video VBR
  3Mbps

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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
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