Audio/Video compression An introduction
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Audio/Video compressionAn introduction
Alain Bouffioux
December, 20, 2006
December, 20, 2006AV Compression / Alain Bouffioux
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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
December, 20, 2006AV Compression / Alain Bouffioux
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Introduction - The evolution of Audio/Video consumer products and the role of compression techniques.
Audio & Video compression principles
Audio demonstration
Video demonstration
Agenda
December, 20, 2006AV Compression / Alain Bouffioux
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Moore’s law
Number of transistors per square inch doubles every 18 months
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Moore’s law today
Cost of a transistor divided by one million in 30 years
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Moore’s law today (2)
“Self-fulfulling prophecy” = roadmap for the semiconductor industry
Itanium 2 (2004, 592,000,000)
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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…)
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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.
ConsumerConsumerComputerComputer
CommunicationCommunication
CDCDDVDDVD
Receiver Digital TV orReceiver Digital TV orResidential gatewayResidential gateway
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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.
RG Home NetworkWorld-wide
communicationinfrastructure
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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...
Network
Local server
Internet
Local server
About 1000 homes
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The evolution of CE products (4)
The Residential gateway as a key element of the home network
Home Network
Residential Gateway
To telephone Network
To satelliteNetwork
To cable Network
Computer
DVD Jukebox
Television
DiskRecorder
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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
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Compression is one among the various factors (all powered by semiconductor progresses) that enable multimedia technologies.
Factors enabling such evolution
Software (methodology,user interface ...)
International cooperation(interoperability &economy of scale)
Disc capacity (DVD), communicationgoing digital (xDSL, DVB, IP......)
Multimedia
Electronics(Memory capacity,clock frequency,µP architecture, ...--> decoding at low cost
Audio/VideoCompression(e.g. CCIR601 vs MPEG)
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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 products
Technology push Market pull (user centric approach)
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Introduction - The evolution of Audio/Video consumer products and the role of compression techniques.
Audio & Video compression principles
Audio demonstration
Video demonstration
Agenda
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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
Audio VideoSpectral
SensitivityGood Bad
SpatialSensitivity
Bad Good
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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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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
Audio waveform (time)
time
The need for more compression (1/5)
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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 = (576*720)*25*16 = 166 Mbit/sec
The need for more compression (2/5)
720 samples
576lines
Video image
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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)
But quality was judged too poor (about VHS quality)
Compression
Video : 166 Mbit/sec
Audio : 1.4 Mbit/sec
1.4 Mbit/sec
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The need for more compression (5/5)
MPEG-2 target– Program stream (DVD)
– Transport stream (DVB)
Compression
1 program(video, multichannelaudio, ....)
= motivation for the capacityincrease of the CD (--> DVD)
3-9 Mbit/sec (variable bitrate)(but higher quality than MPEG-1)
Compression
n programs(video, multichannelaudio, ....)
about 40 Mbit/sec (constant bitrate)(DVB-Satellite & DVB-Cable)
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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,DCT
The original signal and the one obtained after encoding and decoding are identical
DecompressionCompressionFc(x,y,t)
Rc kbps Ri < Rc
Fp(x,y,t) = Fc(x,y,t)
Rp = Rc
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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
DecompressionCompressionFc(x,y,t)
Rc kbps Ri < Rc Rp = Rc
Fp(x,y,t) <> Fc(x,y,t)
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Introduction - The evolution of Audio/Video consumer products and the role of compression techniques.
Audio & Video compression principles
Audio demonstration
Video demonstration
Agenda
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Audio Demonstration
From “Borderline” Madonna - Stereo - 16 bit/channel
Compression used AAC
Compression
Decompression
Original
-
32kbps
128kbps
64kbps
16kbps
705 kbps
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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)
Example:Double blind test
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MOS scale (2/2)
Compressed
3
1
4
Impairmentscale5
Min value
Sequence2 3
Original
Mean value
Max value
Original signal
Listener answers to :1. Which signal is the original ? 2 or 3 ?2. Grade the other one ?
Exchange box(Random for listener)
Selector(controlled by listener)
Compressed signal
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Introduction - The evolution of Audio/Video consumer products and the role of compression techniques.
Audio & Video compression principles
Audio demonstration
Video demonstration
Agenda
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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)
Constantbit rate
Bitrate
Complex
Distorsion
Simple
Constant quality
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Video demonstration
MPEG-1 Example Video CD standard(288*352)video – CBR 1.4 Mbps
MPEG-2 ExampleDVD standard(576*720)video – VBR ~3Mbps
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The compression trade-offCompression techniques are still making progress
Trade-off Complexity/Quality/Bit Rate
New technique may result in new trade-off
Quality
Bitrate
Complexity
MPEG Layer 1
MPEG Layer 2
MPEG Layer 3
MPEG AAC
Other TechniqueSpeech coding
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