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Alain Bouffioux - Philips Hasselt 1 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Audio & Video Compressionand its Application inConsumer Products
Alain Bouffioux - Philips Hasselt 2 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Agendau Introduction - The evolution of Audio/Video consumer
products and the role of compression techniques.
u Audio & Video compression principles
u Audio compression
u Video compression
u Audio/Video synchronisation
u The MPEG model and its situation in a communication context
u Application to DVD (Digital Versatile Disc)
u Application to DVB (Digital Video Broadcasting)
u Conclusion
Alain Bouffioux - Philips Hasselt 3 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
u Introduction - The evolution of Audio/Video consumerproducts and the role of compression techniques.
u Audio & Video compression principles
u Audio compression
u Video compression
u Audio/Video synchronisation
u The MPEG model and its situation in a communication context
u Application to DVD (Digital Versatile Disc)
u Application to DVB (Digital Video Broadcasting)
u Conclusion
Agenda
Alain Bouffioux - Philips Hasselt 4 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The evolution of our products (1/5)
ConsumerConsumerComputerComputer
CommunicationCommunication
CDCDDCCDCC
CD-iCD-i
DVDDVD
STBSTB
Alain Bouffioux - Philips Hasselt 5 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The evolution of our products (2/5)u The STB (Set-Top-Box) as the link between the home and the
world-wide information infrastructure.
STB Home NetworkWorld-wide
communicationinfrastructure
Alain Bouffioux - Philips Hasselt 6 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The evolution of our products (3/5)u The STB (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
Up to 800 homes
Alain Bouffioux - Philips Hasselt 7 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The evolution of our products (4/5)u The STB as a key element of the home network
Home NetworkHome Network
Residential Residential GatewayGateway
To telephone NetworkTo telephone Network
To satelliteTo satelliteNetworkNetwork
To cable NetworkTo cable Network
ComputerComputer
DVD DVD JukeboxJukebox
TelevisionTelevision
DiskDiskRecorderRecorder
Alain Bouffioux - Philips Hasselt 8 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The evolution of our products (5/5)u 3C Convergence - Progressive
u New products combine all 3 functions
u Products always more and more complex
u Working in group becomes more and more important
u Philips international co-operation(avoiding to reinvent the wheel, concentration on corecompetencies)
u Products have always new features
u Lifetime of products is always shorter
u The DVD will also be provided with the communicationfeature (IEEE1394 bus) for home bus integration.
Alain Bouffioux - Philips Hasselt 9 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Compression is one among the various factors that enablemultimedia:
Software (methodology,user interface ...)
International cooperation(interoperability &economy of scale)
Disc capacity (DVD), communicationgoing digital (Modems, xDSL, ATM ...)
Multimedia
Electronics(Memory capacity,clock frequency,µP architecture, ...--> decoding at low cost
Audio/VideoCompression(e.g. CCIR601 vs MPEG)
Factors enabling such evolution
Alain Bouffioux - Philips Hasselt 10 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Agendau Introduction - The evolution of Audio/Video consumer
products and the role of compression techniques.
u Audio & Video compression principles
u Audio compression
u Video compression
u Audio/Video synchronisation
u The MPEG model and its situation in a communication context
u Application to DVD (Digital Versatile Disc)
u Application to DVB (Digital Video Broadcasting)
u Conclusion
Alain Bouffioux - Philips Hasselt 11 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Compression in first A/V Products (1)u First Audio/Video products make compression without
knowing it was compression.
u How ?By removal of irrelevancies
u Audio and Video characteristics
Audio VideoSpectral
SensitivityGood Bad
SpatialSensitivity
Bad Good
Alain Bouffioux - Philips Hasselt 12 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Compression in first A/V Products (2)u Audio products
From 2 to 7.1 channels are enough to provide the spatialresolution.
u Video productsThree colours (RGB) are enough to provide the spectralresolution.
Alain Bouffioux - Philips Hasselt 13 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
u Audio: Compression needed in spectral domain
u 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)
Alain Bouffioux - Philips Hasselt 14 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
u Video: Compression needed in spatial domain
u 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
Alain Bouffioux - Philips Hasselt 15 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The need for more compression (3/5)u 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
Alain Bouffioux - Philips Hasselt 16 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The need for more compression (4/5)u MPEG-1 target
(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
Alain Bouffioux - Philips Hasselt 17 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The need for more compression (5/5)u 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)
Alain Bouffioux - Philips Hasselt 18 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Principles of compression (1/2)u Compression (or source coding) is achieved by suppressing
information :
∗ redundant information∗ irrelevant information
u Suppression of redundant information ⇒ lossless compressionexample: PCM to DPCM,DCT
The original signal and the one obtained after encodingand decoding are identical
DecompressionCompressionFc(x,y,t)
Rc kbps Ri < Rc
Fp(x,y,t) = Fc(x,y,t)
Rp = Rc
Alain Bouffioux - Philips Hasselt 19 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Principles of compression (2/2)u Suppression of irrelevant information
⇒ lossy compressionExample: bandwidth limitation, masking in audio
The original signal and the one obtained after encodingand 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)
Alain Bouffioux - Philips Hasselt 20 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Audio DemonstrationFrom “Borderline” Madonna - Stereo - 16 bit/channel
Compression used AAC
Compression
Decompression
Original
-
32kbps
128kbps
64kbps
16kbps
705 kbps
Alain Bouffioux - Philips Hasselt 21 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
MOS scale (1/2)u Signal distorsion is not a good measure of the performance of a
loosy compression method⇒ an other method is necessary: MOS scale (Mean OpinionScore)
u The five-grade CCIR impairment scale (Rec.562)1(Very annoying), 2(Annoying), 3(Slightly annoying),4(Perceptible but not annoying), 5(Imperceptible)
u Example:Double blind test
Alain Bouffioux - Philips Hasselt 22 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
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
Alain Bouffioux - Philips Hasselt 23 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Compression to VBR or CBR
u CBR (Constant Bit Rate) vs VBR (Variable Bit Rate)
u Scene more complex ⇒ Higher bit rate for same qualityu CBR ⇒ variable quality (example : Video CD artefact)u Constant quality ⇒ VBR necessary (e.g.: DVD-Video)
Constantbit rate
Bitrate
Complex
Distorsion
Simple
Constant quality
Alain Bouffioux - Philips Hasselt 24 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Video demonstration
Alain Bouffioux - Philips Hasselt 25 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The compression trade-offu Compression techniques are still making progress
u Trade-off Complexity/Quality/Bit Rate
u New technique may result in new trade-off
QualityQuality
BitrateBitrate
ComplexityComplexity
MPEG Layer 1MPEG Layer 1
MPEG Layer 2MPEG Layer 2
MPEG Layer 3MPEG Layer 3
MPEG AACMPEG AACOther TechniqueOther TechniqueSpeech codingSpeech coding
Alain Bouffioux - Philips Hasselt 26 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Agendau Introduction - The evolution of Audio/Video consumer
products and the role of compression techniques.
u Audio & Video compression principles
u Audio compression
u Video compression
u Audio/Video synchronisation
u The MPEG model and its situation in a communication context
u Application to DVD (Digital Versatile Disc)
u Application to DVB (Digital Video Broadcasting)
u Conclusion
Alain Bouffioux - Philips Hasselt 27 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Audio compression in MPEG (1/5)u Based on psycho-acoustics
u Compress the bit rate without affecting the quality perceivedby the human ears (based on the imperfection of human ears)
u Removal of irrelevancies
u 4 main principles :∗ Threshold of audibility∗ Frequency masking∗ Critical bands∗ Temporal masking
Alain Bouffioux - Philips Hasselt 28 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Audio compression in MPEG (2/5)u Principle 1: Threshold of audibility
⇒ Not all frequency components need to be encoded with thesame resolution. Nr_bit(f) = (signal/threshold)db/6
0.2
Frequency (kHz)
20
0
0.02 0.10.05
100
80
60
40
Sound level(db)
50.5 1 2 2010
Alain Bouffioux - Philips Hasselt 29 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Audio compression in MPEG (3/5)u Principle 2: Frequency masking
⇒ Analysis of the incoming signal
0.2
Frequency (kHz)
0
20
0.050.02 0.1
60
40
80
Sound level(db) 100
Masked signal
0.5 1 2 5 10 20
New threshold of audibilitydue to masker signal
Masker signal
Alain Bouffioux - Philips Hasselt 30 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Audio compression in MPEG (4/5)u Principle 3: Critical bands
∗ Human ear may be modelled as a collection of narrow band filters∗ Bandwidth of these filters = critical band∗ critical band
(
Alain Bouffioux - Philips Hasselt 31 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Audio compression in MPEG (5/5)u Principle 4: temporal masking
⇒ selection of the frame duration for frequency analysis andencoding.
0~(-10msec) 0
Envelope of masker
Pre masking
Level(db)
Post masking
Simultaneous masking
Time~100msec
Alain Bouffioux - Philips Hasselt 32 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
An enabling tool : the filter bank (1/2)
Digital audio signal, Fs
ENCODING / DECODING
Reconstructed signal, Fs
Synthesis
INTERPOLATION
Analysis
DECIMATION
n subband signals, Fs
Filter bank
n subband signals, Fs
n subband signals, Fs/n
n subband signals, Fs/n
Filter bank
Alain Bouffioux - Philips Hasselt 33 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
An enabling tool : the filter bank (2/2)u After decimation, same bit rate as original signal, but signal
decomposed in various frequency ranges ⇒ possibility of frequency based compression
u Filter-bank:Aliasing occurs due to decimation
u It exists a class of filter-bank such that aliasing is compensatedin synthesis filter : QMF (Quadrature Mirror Filter) but highcomplexity
u Pseudo-QMF (Polyphase filter bank) is used. Has goodcompromise between computation cost and performances
u Remark : Aliasing may occur if signal in a adjacent band is notreconstructed with an adequate resolution.
Alain Bouffioux - Philips Hasselt 34 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The MPEG encoder
Signal to mask level for each subband(quantisation information)
Psychoacousticmodel.
Digital audioinput
Subbandsamples
FilterBank
Ancillary data
Quantisedsamples
Bitallocation
Bitstreamformatting
Encodedbitstream
Alain Bouffioux - Philips Hasselt 35 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The MPEG filter banku In MPEG, 32 equal-width subbands are used
u For each subband, necessity to define the maximum signallevel and the minimum mask level.
u BUT, at low frequencies : bandwidth of subbands > critical bands
u ⇒ Necessity to rely on an FFT in order to compensate thelack of frequency selectivity of filterbank at low frequencies
Alain Bouffioux - Philips Hasselt 36 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Psychoacoustic model & Bit allocation(1/2)
u An FFT compensates the lack of frequency selectivity offilterbank at low frequencies
u FFT : 512 samples (layer 1) & 1024 samples (layer 2)resolution for layer 1 : Fs/512 < 100 Hz
u A psychoacoustic model based on the FFT computes the signalto mask ratio for each subband (1 bit = 6db)
u Ideally, after allocation, quantisation noise < masking level
u The scale factors are computed for each subband from thefilterbank output (floating point representation of samples)
u The bit allocator adjust the bit allocation in order to meet thebitrate requirement.
u The bitstream syntax is dependent of the MPEG layer (See later)
Alain Bouffioux - Philips Hasselt 37 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Psychoacoustic model & Bit allocation(2/2)
Frequency
Signal/MaskLevel(db)
Level(db)
Signal level
Bit allocation= 1 bit
Frequency
Mask level
Alain Bouffioux - Philips Hasselt 38 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The MPEG decoderu Decoder is simple (Complexity is at encoder side)
u Remark 1: DCC is MPEG-1 but DCC encoder has no FFT,relies only on power in the 32 subbands ⇒ Higher bit rate (320 kbps) to reach transparent quality
u Remark 2: MPEG specifies bitstream syntax only. Encoderare given for information. Possibility of improvement.
SubbandSamplesrecons- truction
Bitstreamunpacking
Encodedbitstream
Ancillarydata
Subbandsamples
Filterbank
Decoded audio signal
Alain Bouffioux - Philips Hasselt 39 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Audio features in MPEGu MPEG1 :
∗ Mono/stereo/dual/joint stereo (Possibility Dolby surround)∗ Sampling frequencies : 32, 44.1 & 48 kHz∗ 3 layers : trade-off complexity/delay versus coding
efficiency of compression
∗ Various bit rate : trade-off quality versus bitrate
u MPEG2 :∗ 5.1 channels∗ Sampling frequencies extended to 16, 22.05 & 24 kHz
Alain Bouffioux - Philips Hasselt 40 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Dolby surround principles (1/5)u 4 channels carried by stereo pair ⇒ same tools as for stereou Compatible with stereo installation
+90°
-90°
Phaseshifter
Lt
RtSurround Surround
Left
Configuration
Center Right
Center(C)
- 3 dB- 3 dB
Right (R)
Surround(S) 100 Hz -
7000 Hz
BP
- 3 dB- 3 dB
From 4 channels to 2 channels
Left (L)
Alain Bouffioux - Philips Hasselt 41 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Dolby surround principles (2/5)
Encoding equations Simple decoder
Lt L .1
2
C ..j1
2
S L Lt ⇒ Ld L .1
2
C ..j1
2
S
Rt R .1
2
C ..j1
2
S R Rt ⇒ Rd R .1
2
C ..j1
2
S
CRt Lt
2⇒ Cd .
1
2
L .1
2
R C
SLt Rt
.2 j⇒ Sd ..j 1
2
L ..j1
2
R S
Alain Bouffioux - Philips Hasselt 42 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Dolby surround principles (3/5)
3 dBS
3 dB
3 dB
L C
3 dB
R
u Simple decoder provides only 3 dB channel separation(See previous equations) ⇒ Need for improvement ⇒ Dolby Surround pro-logic decoder (next slide)
Alain Bouffioux - Philips Hasselt 43 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Dolby surround principles (4/5)Dolby surround pro-logic decoder
BP
C'
S'
R'
L'
Rt
-3 dB
Lt
-3 dB Direc-tionCom-pen-sation-90°
Rd
Sd
VCA
VCA
Cd
Ld
VCA
VCA
Alain Bouffioux - Philips Hasselt 44 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Dolby surround principles (5/5)Performance of Dolby pro-logic decoder
Channel separation larger than 35 dB
> 35 dB
S
> 35 dB
> 35 dB
L
> 40 dB
C
> 35 dB
> 40 dB
R
Alain Bouffioux - Philips Hasselt 45 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
5.1 surround soundMPEG-2 surround configurations (front/back)
u 3/2
u 3/0 + 2/0
u 3/1
u 2/2
u 2/0 + 2/0
u 3/0
u 2/1
u 2/0
u 1/0
+ LFE (opt.)(Fs/96)15-120Hz
SurroundLeft
SurroundRight
(+LFE)
CenterLeft Right
Alain Bouffioux - Philips Hasselt 46 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Virtualisationu Virtualisation has no direct relation with the MPEG standard.
It is considered here only because it may be implemented insome of the future audio products (DVD, STB ...)
u Virtualisation is a product feature.
u It allows reproduction of surround information (5.1, 3/1) on astereo installation.
Alain Bouffioux - Philips Hasselt 47 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Virtualisation principle
u Virtualisation = processing of the signal in such a way thesource of the signal is perceived at a selected position outsidethe loudspeaker axis (virtual loudspeaker).
u Drawback : very sensitive to listener position (stability)
u Remark : a mono signal coded in normal stereo is perceivedbetween the two loudspeakers
Listener
Real loudspeakerProcessing
Mono signal
Virtualloudspeaker
Alain Bouffioux - Philips Hasselt 48 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Stereo widening
u Also called Q-sound , incredible sound, azimuth positionning...
u The stereo sources are positionned at virtual locations forimproving the stereo effect (cheap analog solution exists)
u Real sound comes from real loudspeakers. Perceived sound isas if stereo signals were coming from virtual loudspeakers
Listener
Real loudspeakerProcessing
Stereo signal
Virtualloudspeaker
Alain Bouffioux - Philips Hasselt 49 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Virtual surroundu Virtual surround gives on a stereo installation the subjective
effect of a multichannel configuration.
u Each channels is virtually positionned at a location around thelistener.The stereo installation performs the addition of the processedsignals for each audio channel.
u Real sound comes from a stereo installation. Perceived soundis as if the various surround signals were coming from somevirtually located loudspeakers.
Alain Bouffioux - Philips Hasselt 50 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Summary of surround aspects
Remarks about Dolby surround pro-logic :
Only carrier is stereo, source & presentation are multichannel
Compatible with stereo installation (no surround effect except in the case ofsurround virtualisation)
Stereo receiver Multichannel receiver
Stereo source Stereo widening(incredible sound,azimuth positioning)
3-D special effects(hall, theatre, stadium)
multichannel source Virtual surround Multichannel output
Alain Bouffioux - Philips Hasselt 51 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Agendau Introduction - The evolution of Audio/Video consumer
products and the role of compression techniques.
u Audio & Video compression principles
u Audio compression
u Video compression
u Audio/Video synchronisation
u The MPEG model and its situation in a communication context
u Application to DVD (Digital Versatile Disc)
u Application to DVB (Digital Video Broadcasting)
u Conclusion
Alain Bouffioux - Philips Hasselt 52 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Video compression in MPEG (1/6)u Principles
∗ removal of intrapicture redundancy :Image is decomposed in 8*8 pixels subimages.Each subimage contains redundant informationDCT transfomation (in frequency domain) decorrelates theinput signal.( most energy in low spatial frequencies)
∗ removal of interpicture redundancy :coding of difference with an interpolated picture (movingvectors)
∗ high frequent spatial frequencies quantized with lowerresolution than low ones(remove irrelevancy)
∗ zig-zag scan and VLC (remove redundancy)
Alain Bouffioux - Philips Hasselt 53 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Video compression in MPEG (2/6)u Result
∗ 4:2:2 CCIR 601 resolution : 166 Mbps(=25images/sec *576lines* 720pixels* 2(lum & chrom)*8bits)⇒ ± 3-4 Mbps (mean) in MPEG2
∗ 4:2:0 SIF resolution : 30 Mbps(=25 images/sec *288 lines *352pixels* 1.5(lum & chrom)*8bits)⇒ ±1.2 Mbps (CBR) in video CD (MPEG1)
Alain Bouffioux - Philips Hasselt 54 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Video compression in MPEG (3/6)u Spatial redundancy reduction (DCT example)
158 0 -1 0 0 0 0 0 -1 -1 0 0 0 0 0 0 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
139 144 149 153 155 155 155 155144 151 153 156 159 156 156 156150 155 160 163 158 156 156 156159 161 162 160 160 159 159 159159 160 161 162 162 155 155 155161 161 161 161 160 157 157 157162 162 161 163 162 157 157 157162 162 161 161 163 158 158 158
158 0 -1 -1 -1 -1 EOBzig-zag scan
1260 -1 -12 -5 2 -2 -3 1 -23 -17 -6 -3 -3 0 0 -1 -11 -9 -2 2 0 -1 -1 0 -7 -2 0 1 1 0 0 0 -1 -1 1 2 0 -1 1 1 2 0 2 0 -1 1 1 -1 -1 0 0 -1 0 2 1 -1 -3 2 -4 -2 2 1 -1 0
DCT
Quantisation
Alain Bouffioux - Philips Hasselt 55 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Video compression in MPEG (4/6)u Temporal redundancy reduction
B
5
Bi-directional prediction
I : Intra-coded pictureP: Predicted pictureB: Bi-directionally interpolated picture
4
B
Order ofpresentation
Order oftransmission
BI P
0 3
B P
1 2 6
B
Prediction
I B P B
Increase of compressionrate
0 1 2 3 4
7
B P B
5 9
B I P
8
P B B P I B
86 7 9
Alain Bouffioux - Philips Hasselt 56 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Video compression in MPEG (5/6)u Model of a possible encoder
Buffer
Data
Regulator
Motion estimation
Motionvectorsand modes
Format conversion and picture reorder
Inputpictures
Picturestore andprediction
1/DCT
DCT VLC
1/Q
Q Multi-plex
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Video compression in MPEG (6/6)u MPEG1 en MPEG2 video features
∗ MPEG1F sequential picture
F resolution : SIF format 288(240)*356*24,25 or 30 Hz
∗ MPEG2F sequential or interlaced
F various levels : low level (SIF: 288*356), main level (CCIR601: 576* 720), high 1440 level (HDTV: 1152*1440), high level (EQTV:1152*1920)
F various profiles (toolboxes) : simple profile (No B picture), mainprofile (=MPEG1+interlaced), SNR scalable profile (allows gracefuldegradation (noise improvement at same resolution), spatial scalableprofile (hierarchical coding : improvement at higher resolution), highprofile.
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Agendau Introduction - The evolution of Audio/Video consumer
products and the role of compression techniques.
u Audio & Video compression principles
u Audio compression
u Video compression
u Audio/Video synchronisation
u The MPEG model and its situation in a communication context
u Application to DVD (Digital Versatile Disc)
u Application to DVB (Digital Video Broadcasting)
u Conclusion
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Synchronisation
Synchronisation in the multimedia context
refers to the mechanism that ensures a temporal
consistent presentation of the audio-visual
information to the user
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Intramedia synchronisation
∆T between capture & presentation = Constant ≡ Same clock frequency & Data on time ⇒ Need for corresponding tools
Network
∆
∆ T1T2 = ∆
T1
Capture time
Audio signal Encoder
∆T = Constant
Decoder
Presentation time
Audio signal
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Intermedia synchronisation
∆T_Audio = ∆T_Video ≡ (Sampled at the same time ⇒ Presented at the same time) ⇒ Possible tools : common time base and presentation control (media
synchronisation with the common time base)
Ex.: Lip_sync (requirement: |delay_difference| < 80msec)
Network
T_audio = Constant
T_video = Constant = Capture time
∆
Video signal
Audio signal
Encoder
Capture time∆
T_Audio ∆Presentation time
Decoder
Video signal
Audio signal
Presentation time
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Recovery of clock in CBRu CBR = Constant Bit Rate
u if the clock to recover is synchronous with transport clock ⇒Recovery of clock but not of common time base
u Remark : possibility to slave DSM to local clock
Filter
CBR stream
Phaseerror
Filling level
50%
Time Information carriedby each sample
VCO
Processing
Recoveredclock
time
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Recovery of clock and time base in VBRu VBR = Variable Bit Rate
u Need for insertion of time stamps (OUTPUT TIME)Output time stamp says for example : “It is now 16h25”Receiver adjusts its own horloge to the received time stamp
u Recovery of clock & of common time baseTime information carriedonly by time stamps
Time stamp extraction
Time counter
Recovery of clock & time
First time stamp
Others
Clock
Data stream
Data stream
Time stamps
Counter
Recovered clock
Error Filter VCO
VBR Stream
Counter sample(=Time stamps)
Channel
Time stamps
Alain Bouffioux - Philips Hasselt 64 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Synchronisation with common time baseu Insertion of time stamp (=INPUT TIME)
Input time stamp says : “Sample has been sampled at 16h29”.Receiver presents the sample at (its input time stamp + maximum encodingand decoding delay).Alternative: transmission of presentation time stamp (input time+delay)
Buffering
Mediaoutput
Media input
Time clock(Recovered)
Comparison of time clockwith sampled time clock
Sample "Time clock"Assemble frame
Time clock
Timestamp
Processing
Processing
Channel
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Getting data on timeu “On time” ⇒ Not too late, not too early
No buffer over- or underflow
u Flow control : not applicable in broadcasting
u Common time base andDefinition of a standard target decoder that describes the dataconsumption pattern of the receiver.
u Remark: Direct MPEG (microsoft) does not use timeinformation for clock recovery but relies on flow control
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Streamsu Idea of continuity (pipelining)
u Carry time information for clock recovery
u No flow control (allows broadcasting)The emitter must have a precise knowledge of the receiver dataconsumption pattern (explicit in MPEG STD)
u Just-in-timeShorter delay and smaller buffer size than with flow control
u Two aspects in synchronisation :Clock recovery & timing control (model & buffering)
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Requirement on the channel for streamtransport
Data information ⇒ BER (Bit Error Rate) requirementNo repetition of frame possible ⇒ FEC (Forward ErrorCorrection)
Time information ⇒ No jitter
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Agendau Introduction - The evolution of Audio/Video consumer
products and the role of compression techniques.
u Audio & Video compression principles
u Audio compression
u Video compression
u Audio/Video synchronisation
u The MPEG model and its situation in a communicationcontext
u Application to DVD (Digital Versatile Disc)
u Application to DVB (Digital Video Broadcasting)
u Conclusion
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What is MPEG ? (1/2)
u Moving Picture Expert Group
u International standard (ISO/IEC)⇒ Interoperability & economy of scale
u Compression of audio and video and multiplexing in a singlestream
u Definition of the interface not of the codecs⇒ room for improvement
u MPEG-1 : until 1.5 Mbps, for DSMProgressive picture, stereo (Dolby surround)
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What is MPEG ? (2/2)u MPEG-2 : Various bit rates (CBR & VBR)
Program stream for DSM, transport stream for networkInterlaced picture, 5.1 audio channelsDefinition of various video levels (e.g. CCIR601 resolution: 4-9 Mbps, HDTV:15-25 Mbps) and profiles
u MPEG-3 : Cancelled, integrated in MPEG-2(Initially : for HDTV)
u MPEG-4 : standard for audio, video and graphics in interactive2D and 3D multimedia communication.(Initially : low bit rate for real-time personal communication)
u MPEG-7 : Multimedia contents description interface
u MPEG-21 : Focus on multimedia distribution and on DRMaspects.
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The MPEG model (1/2)
Audiodecoder
Audio signal
Videosignal
Presented signals
Multiplexer
Videodecoder
Captured signals
Audioencoder
Videoencoder
Audio signal
Videosignal Digital storage medium
orNetwork
Transmission channel
Demulti-plexer
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The MPEG model (2/2)u Compression of audio & video and multiplexing in a single
stream
u Guarantees intramedia and intermedia synchronisation.
u MPEG defines an interface∗ bitstream syntax∗ timing of the bitstream ⇒ STD specifying timing requirement (ideal
model)
u Consequences:∗ Decoder should compensate deviations from STD∗ Network should correct jitter introduced by the channel (RTD-LJ)
u MPEG stream must be adapted to transmission channelformatting, error correction, channel coding (b.v.video-CD)
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Components of the MPEG standardu The MPEG standard is composed of 3 main parts :
∗ Audio : Specifies the compression of audio signals∗ Video : Specifies the compression of video signals∗ System : specifies how the compressed audio and video signals are
combined in the multiplexed stream (program stream or transportstream).
u Each part specifies :∗ The bitstream syntax∗ The timing requirement and the related information (bit rate, buffer
needs)
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Synchronisation Mechanism (1/2)
System decoderanddemultiplexer
Multiplexer and systemencoder
Audiodecoder
Videodecoder
ComparisonPTS and STCand presentation
Videooutput
ComparisonPTS and STCand presentation
Audiooutput
Extractionof PCR (SCR)
STC
Audioencoder
Videoencoder
Assemble pictures,Sample STC for PTS
Videoinput
Assembleaudio frames,Sample STCfor PTS
Audioinput
Sample STCfor PCR(SCR)
STC
Transmission channel
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Synchronisation Mechanism (2/2)u PCR for TS & SCR for PS (but same concept)
u Clock & time base recovery: Time-stamping at OUTPUT(PCR included in TS multiplex, SCR in pack header)
u Audio & video clock locked to STC ⇒ easy recovery (see nextslide)
u Synchronisation of audio & video to common time base (Timestamping at Input)
u STD is defined (because of the absence of flow control)streams are such that STD buffers never over- or underflow
u In TS, many program in a single stream but unique clock perprogram.
u Time information ⇒ No Jitter for transport
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Clock recovery in receiver
VCO Audio clockdivider
Video clockdivider Video
clock
Audioclock
Audiooutput
STC
ComparisonPTS and STCandPresentationDecoded
audio
PTS
STC(Counter)
PCR
STC
Error Low Pass Filter(Integrator)
Load first PCR
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MPEG program & transport streamsu Program streams:
∗ Relatively error free environment∗ program stream packet may have variable and great length∗ Single time base
u Transport streams:∗ environment where errors are likely∗ many programs (independent time base)∗ Transport stream packet : fixed, 188 bytes∗ Contains tables
Alain Bouffioux - Philips Hasselt 78 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
MPEG in a communication context (1)“Typical” communication system
Channelencode
Channeldecode
Bit-stream
Sourcedecode
Informationsink
Digitaloutput
Format Decrypt
SourceencodeFormat
Informationsource
Digitalinput
Encrypt
Synchro-nisation
Digitalwaveform
Otherdestination
Demodu-late
Demulti-plex
Multipleaccess
Modu-late
Multi-plex
Channelbits
Othersources
Multipleaccess
Channel
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MPEG in a communication context (2)u MPEG : Source coding only (bit rate reduction) + multiplexing
u The MPEG stream must be adapted to the channel in whatconcern its physical characteristics and in order to get therequired QoS (Quality of Service) & Security∗ Encryption∗ Channel coding (forward error correction, interleaving, modulation
codes)
∗ multiplexing & formatting∗ modulation (frequency allocation)∗ multiple access method
u Some channels : CD/DVD - satellite - cable - ATM - 1394
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MPEG in a communication context (3)u A simple view of MPEG in the communication context
VideoEncoder
MPEG2 compression layer
Audioencoder
Audio,videosources
ES(ElementaryStream)
Adap-tationto thechannel
PS(1 pro-gram)
MPEG2 system layer
PSMulti-plexing
Adap-tationto thechannel
DVB, DVD ...
Disc
Satellite
TSMulti-plexing
TS(n pro-grams)
Adap-tationto thechannel Cable
TS (Transport Stream)orPS (Program Stream)
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u Introduction - The evolution of Audio/Video consumerproducts and the role of compression techniques.
u Audio & Video compression principles
u Audio compression
u Video compression
u Audio/Video synchronisation
u The MPEG model and its situation in a communication context
u Application to DVD (Digital Versatile Disc)
u Application to DVB (Digital Video Broadcasting)
u Conclusion
Agenda
CD : Some conceptsu Hard disk vs compact disc : more differences than just storage
technique.HD developed for data storage and recording, CD developed forstream storage (CD-DA) ⇒ their basic differences
u Questions∗ track form?∗ read direction? Why?∗ CAV or CLV? Why?∗ Access time : CD-ROM vs HD?∗ Data storage: on which face?∗ Production method?∗ Capacity?∗ Sensitivity to error? Diameter of a possible hole?∗ Standard = Interface definition : CD vs HD ?
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CD-DA: Encoder model (1/3)
Modulation
6 samples = 24 bytes= 1 frame
EFM + 3 merging bits
Synchronisation pattern27 bit/frame
561 bits / frame
CD-ROM1 sector = 98 frames75 sectors/sec.
588 channel bit/frame
Right
LeftA/D conversion
PCM 44.1 kHz16 bit/sample/channel
Subcode(1 byte / frame)
Physical layer
Error correctionencoding
32 bytes/frame
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CD-DA: Encoder model (2/3)u The CD-DA physical layer adapts the input stream (audio) to
the requirements of the channel
∗ Modulation : EFM (Eight to fourteen modulation + 3merging bits)Pit & land length (number of successive 0 or 1 as written todisc): between 3 and 11 channel bitsDC free codefor adaptation to the channel bandwidth & for clockrecovery considerations.
∗ Error correction (Cross-interleaved Reed-Solomon code)Interleave placed between C1 & C2 ECC.Next slide presents only principles and not real CDimplementattion.
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CD-DA: Encoder model (3/3)∗ Error correction : addition of redundancy in order to be able
to correct errors (e.g. RS(28,24,5)*RS(32,28,5))Principle :
∗ Interleaving : time diversity in order to deal with errorburst.Successive errored channel bits (burst error) do not damagethe same Reed-Solomon table.
4 bytesC2 codewords
24 bytes
28 bytes
Data
4 bytes
C1code-words
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CD-ROM encoder model
2336 bytes
Mode 1
Mode 2
Mode 1
2336 bytes
Additionalerror detection &error correctionencoding
Optional EDC 4 bytes
User data 2324 bytes
Subheader 8 bytes
Subheader 8 bytes
User data 2048 bytes
Sync Pattern 12 bytes
Additionalerror detection &error correctionencoding
User data 2048 bytes
Zeroes 8 bytes
Header 4 bytes
Header 4 bytes
2340 bytes
For EDC only
Video-CD uses CD-ROM mode 2 sectors
OR
12 bytes
2340 bytesScramblingOR1 CD-ROM sector= 2352 bytes
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The CD standards
CD-BGMVideo-CD93
CD-RW96
CD-ROM1984
Photo-CD
CD-ROM-XA
CD-bridge
CD-i1987
CD-DA1982
CD-WO90
CD-i Ready
CD-MIDI
CD-G
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From CD to DVD : the motivationu Motivation = increase the capacity
u Why ? - Requirement of the motion picture industry
∗ Playback time : more than 135 min. (duration of 90% offilms)
∗ Picture quality : superior to laser disc∗ Audio quality : 5.1 channels surround∗ Language/subtitles : 3 languages minimum.⇒ capacity needs : more than 4.7 Gbytes
u Where ? - In physical layer
u DVD : developed specifically for audio/video( ≠ video CD).
Alain Bouffioux - Philips Hasselt 89 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The DVD physical layer (1/2)
Recorded sectors
2366 bytes(13 *182 bytes)
8/16modu-lation
37856 channel bits
Synchronisation(2*13)*32 channel bits
38688 channel bits(eqv. to 2418 bytes)
EDC : Error Detection CodeECC : Error Correction CodeCPR-MAI : CoPyRight MAnagement Information
CPR-MAI - 6 bytes
ID (incl. sector#)4 bytes
Data2048 bytes
+EDC
Scrambling
EDC4 bytes
6 bytes
ECC(per group of 16 sectors)
Data sector
2064 bytes(12 * 172 bytes)
RowInter-lea-ving
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The DVD physical layer (2/2)u Objective was the storage of 2K sectors
u Error Correction Code (Reed-Solomon) - add redundancy
u Modulation - time diversity(Number of consecutive 0 : between 2 and 10)Pit and land length : between 3 and 11 (Idem CD)
u Synchronisation : for sector reconstruction.
16 bytesPO (Outer Parity)
172 bytes
192 bytes
16 data sectors
(12 * 172 bytes)*16
10 bytes
PI(InnerParity)
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DVD: the capacity improvement (1/4)u Increase of channel bit density ( gain = 4.50)
Min pit length : (0.83µ ⇒ 0.4µ)Track pitch : (1.6µ ⇒ 0.74µ)Diameter of laser spot (÷ wavelength/NA)Wavelength (780nm ⇒ 640 nm) ⇒ gain = 1.5NA (0.45⇒ 0.60) ⇒ gain = 1.78reduced margin ⇒ gain = 1.68
u Modulation:EFM (8 to 17 bit) ⇒ 8 to 16 ⇒ gain = 1.06
u Error correctionRS(32,28,5)*RS(28,24,5) ⇒ RS(182,172,11)*RS(208,192,17)
⇒gain = 1,16
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DVD: the capacity improvement (2/4)u No subcode ⇒gain = 1.03u Sync pattern ⇒gain = 1.03u Better sector formatting
sector length (2352 bytes ⇒ 2064) ⇒gain = 1.14u Other (e.g. recorded area) ⇒gain = 1.07
Total gain : 7.2
Capacity per side : 650 MBytes (mode 1) ⇒ 4.7 Gbytes
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DVD: the capacity improvement (3/4)
0.6 mm
0.6 mm
0.6 mm
0.6 mm
For layers 0 and 1
A side
Single-layer double-sided disc
Single-layer single-sided disc
0.6 mm
0.6 mm
B side
Dual-layer double-sided disc
0.6 mm
0.6 mm
Dual-layer single-sided disc
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DVD: the capacity improvement (4/4)u Capacity of the various types
Single-layer single-side 4.7 GbytesDual-layer single-side 8.5 GbytesSingle-layer double-side 9.4 GbytesDual-layer double-side 17 Gbytes
Alain Bouffioux - Philips Hasselt 95 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
The 3 components of the DVD-V standard
DVD = DVD (Not “Digital Video Disc”, Not “Digital VersatileDisc”)
DVD-V = DVD - Video
Part 1 : Physical specification
Part 2 : File system specification
Part 3 : Video specification
How blocks may be retrieved. Definition of the file andvolume structure.
How blocks of 2048 bytesare stored on the disc
Contents of the data block.How audio and video are mapped to the block, file and volume structure
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Some DVD-V features (1/2)Presentation data = MPEG program stream, VBR, max peak bitrate = 10.08 Mbps)
Video data 1 stream Mpeg1Mpeg2 (ML@MP)
Audio data max 8 streams Mpeg2 + 7.1 ext.DolbyAC-3Linear PCM (incl. 96 kHz- 24 bits)
Sub picture data max 32 streams Run length encoded(subtitles) Bit map
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Some DVD-V features (2/2)u Seamless playback
Languageparental lockMulti-angle camera
u System menuAudio stream selectionSubtitle selectionAngle
u EncryptionDecryption key hidden on the disc.
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UDF & ISO9660
Part 3:Application Videospecification
Part 2:File system
Part 1:Physical
UDF
Read only
DVD-ROM DVD-Video
Audiospecification
Write-once
UDF | (UDF & ISO9660)
Rewritable
DVD-Audio DVD-R DVD-RAM
The DVD family of products
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Recording on disk - principleu Products: CD-R, CD-RW, DVD-R, DVD-RAM
u CD principle: reflectivity of pits & lands are different.Pits and lands are used to store 0 and 1.
u CD-RW principle: reflectivity of the two phases of therecording material (amorphous, crystalline) are different.Controlling the phase allows storage of 0 or 1.
u To Amorphous state (low reflectivity):T above melting point (600°C) & fast cooling
u To Crystalline state (high reflectivity):T above 200°C for a sufficient time
u Recording: by the laser heating the recording layer
u Reading: by laser as for CD (-> compatibility)
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Agendau Introduction - The evolution of Audio/Video consumer
products and the role of compression techniques.
u Audio & Video compression principles
u Audio compression
u Video compression
u Audio/Video synchronisation
u The MPEG model and its situation in a communicationcontext
u Application to DVD (Digital Versatile Disc)
u Application to DVB (Digital Video Broadcasting)
u Conclusion
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Adaptation to the DVB channel
u Channel coding : transforms the TS in an other sequence ofbits containing the same information than the input stream butmore robust against the imperfections of the transmission onthe physical channelcost : a higher bit rate
u Modulation : transforms an input sequence to an analogwaveform for transmission over the physical channel
Sequence of bits
(Encrypted) TS Channelcoding
Analog waveform
Modulation Physicalchannel
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Channel coding (1/3)u Unlike source coding that removes redundancy,
channel coding adds redundancy in a structured way sothat the decoder be able to detect and/or correct the errorsintroduced by the physical channel.
Channeldecoding
Source decoding
Sink
Source coding
Source Channelcoding
Quasi-error-freechannel (e.g.BER
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Channel coding (2/3)u Channel coding may include :
∗ Spectral modification of the signalfor adaptation to the channel (e.g. remove DC, spectrum shaping likeuniform distribution in the frequency space ...)
∗ FEC : Forward Error CorrectionAddition of redundancy in order to allow error detection and/orcorrection (example : The total of bought articles is similar to a paritybyte)
188 bytes
188 bytes
Allows correction of 8 erroneous bytes
After error correctionencoding
Original sequence
Message Parity bytes
16 bytes
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Channel coding (3/3)∗ Interleaving
Time diversity in order to deal with error bursts.The successive bytes of information are dispersed in time on thetransmission channel in such a way that an error burst does not affectneighbouring bytes.Interleaving is often combined with FEC so that error bursts could becorrected by the FEC.
Example :
AEIMBFJNCGKODHLPQ.....
AEIMBFJ&&&KODHLPQ.....
----> A burst of errors affects bytes belonging to different error correction blocks
Channel
Deinterleaving
AB&DEF&HIJKLM&OPQ.......|---|---|---|---|
Interleaving
ABCDEFGHIJKLMNOPQ.......
& : Erroneous byte| : Beginning of an error correcting block- : Element of an error correcting block
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Modulation in DVB (1/3)u Different modulation techniques :
∗ Cable : QAM∗ Satellite : QPSK∗ Terrestrial : OFDM
u Why ?Modulation technique depends on :
∗ Physical characteristics of the channel∗ Compatibility constraints with actual analog transmission
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Modulation in DVB (2/3)
u Example : influence of SNR on modulation technique selected⇒ QPSK for satellite and QAM for cable
14
1E-7
4
1E-5
1E-6
6 8 10 12
QPSK
BER
0.001
1E-4
0.01
1.0
0.1
16 18
16QAM
20 22
32-QAM 64-QAM
24 26 28 SNR
Alain Bouffioux - Philips Hasselt 107 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Modulation in DVB (3/3)u Satellite
Bandwidth : generally 27-36 MHzSNR low : about 10 db (power transmitted by satellite)direct path
u CableBandwidth : 8 MHz (50Hz countries) - 6 MHz (60Hzcountries)SNR strong (about 25 db)Echoes from impedance mismatch in the network
u TerrestrialBandwidth : idem as cableMultipath interference, signal level variation, ...
Alain Bouffioux - Philips Hasselt 108 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
From TS to the DVB channel
u Some blocks are identical for all standards (Cable, Satellite & Terrestrial)
u Inner & outer : terminology is derived from the view of the quasi-error-freechannel composed of a transmitter and a receiver.
u Satellite & Terrestrial : More sensitive to error ⇒ inner coder is added
QAMmodulation
QPSKmodulation
OFDMmodulation
DVB-C
DVB-S
DVB-T
Spectrumshaping
TS Outercoding
Inner inter-leaver
Innercoding
Inter-leaving
Alain Bouffioux - Philips Hasselt 109 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Agendau Introduction - The evolution of Audio/Video consumer
products and the role of compression techniques.
u Audio & Video compression principles
u Audio compression
u Video compression
u Audio/Video synchronisation
u The MPEG model and its situation in a communicationcontext
u Application to DVD (Digital Versatile Disc)
u Application to DVB (Digital Video Broadcasting)
u Conclusion
Alain Bouffioux - Philips Hasselt 110 A/V compression applied to Consumer Products - ULGDigital Video System - Products & services, Product Innovation AHR-AB00069 - 13/12/00
Questions
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