Introduction to Digital Video Technology Dr' Edward Chow

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Introduction to Digital Video TechnologyDr.
Edward Chow
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Agenda

• Applications
• Image Compression Technology
• Basic Network Planning
• Implementation Examples
• Source CISCO, Microsoft, C-CUBE, WWW.mpeg.org

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Video Applications
Distance Learning Video Conferencing Tele
Medicine Surveillance Broadcast TV
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ConferencingRoom to Room
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ConferencingDesktop
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ConferencingMultipoint
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BroadcastLive
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BroadcastPre-Recorded
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BroadcastVideo Distribution
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Video on Demand
VideoServer
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Video Application Matrix
Point-to- Multipoint
Point-to-Point
Unidirectional

• Considerations
• Video Quality
• Bandwidth
• Latency

Bidirectional
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Agenda

• Applications
• Image Compression Technology
• Basic Network Planning
• Implementation Examples

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Technology
Bandwidth
QoS
ATM
PAL
RSVP
Standards
MPEG-2
H.320
H.323
NTSC
Lossless
Motion JPEG
Lossy
T.120
Latency
H.261
Ethernet
Multicast
ISDN
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Video Quality and Bandwidth
Narrowband ISDN
Broadband Ethernet, ATM
Business Quality
Video ConferenceQuality
VHS/BroadcastQuality
1M
128K
10M
Bits Per Second
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Video Data Requirements
3 Colors x 30 Frames/second 27 MBps 221
Mbps
640
480
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Video Compression Standards
Video Quality
Motion JPEG MPEG-2 MPEG-1 H.261/H.263 MPEG-4
Broadcast Broadcast/HDTV VCR/Business Video
Conf Video Phone
Refer Mercury Technologies for revised bandwidth
requirements
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Video Compression Standards
CompressionRatio
Bandwidth (bits/sec)
Motion JPEG MPEG-2 MPEG-1 H.261/H.263 MPEG-4
10 26 M 3 16 M .5 4 M 128 K 1 M 4.8 K
64 K
727 1 30100 1 25100 1
24200 1 501000 1
Refer Mercury Technologies for revised bandwidth
requirements
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Video Compression Basics

• The basic compression scheme can be summarized as
  follows
• 1. Divide the picture into 8x8 blocks
• 2. Determine relevant picture information
• 3. Discard redundant or insignificant information
• 4. Encode relevant picture information with the
  least number of bits.
• Common functions are
• DCT
• Zig-Zag Scanning
• Quantization
• Entropy Coding
• Motion Estimation

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Discrete Cosine Transform (DCT)

• Two dimensional (2D) DCT maps a picture or a
  picture segment into its 2D frequency components.
• For video compression applications, since the
  variations in the block tend to be low, the great
  majority of these transformations result in a
  more compact representation of the block.
• The block energy is packed into the corresponding
  lower frequency bins.

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Zig-Zag Scanning

• Since the mapping is from lower to higher
  frequencies in the horizontal and vertical
  directions, zig-zag scanning of the resulting 2D
  frequency bins clusters packets of picture
  information from low to high frequencies into a
  1D stream of bins.

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Quantization

• Represent the frequency bins by converting
  amplitudes that fall in certain ranges to one in
  a set of quantization levels.
• Frequency quantization has no "contour"
  distortion effect

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Entropy Coding

• Statistically encoding the most frequently
  occurring patterns with the least number of
  bits.
• A two step process
• Zero Run-Length Coding (RLC)
• Representation of the quantized bins which
  utilizes a pair of numbers.The first number
  represents the number of consecutive zeros while
  the second number represents the value between
  zero-run lengths.
• Huffman Coding
• Assigns a variable length code to the RLC data.
  Huffman tables are computed based on statistical
  properties of the image.

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Motion Estimation

• Compression ratios for motion video sequences may
  be increased byencoding the arithmetic difference
  between two or more successive frames.
• Motion estimation is the process by which
  elements in a picture are best correlated to
  elements in other pictures (ahead or behind) by
  the estimated amount of motion. The amount of
  motion is encapsulated in the motion vector.
• Forward motion vectors refer to correlation with
  previous pictures.
• Backward motion vectors refer to correlation with
  future pictures.
• Motion estimation is an extremely computationally
  intensive operation difficult to implement in
  real-time.

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JPEG Compression

• Encoding
• Decoding

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Motion JPEG
Spatial Compression
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Video Compression
Video Sequence
Group of Pictures


Picture
Block
Macroblock
Slice
8Pixels
8Pixels
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H.261 Compression

• H.261 Encoding
• 8x8 block, 16x16 macroblock
• motion vector is used as a displacement vector to
  fetch a macroblock from the preceding frame to be
  used as a prediction.

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MPEG-1 Compression

• Motion estimation is also allowed over a greater
  range (up to /- 1023). Result in significant
  higher quality.
• Forward predicted frames (called P frames) allow
  macroblocks predicted from past P frames or I
  frames or macroblocks coded from scratch.
• I frames and P frames are used as past and future
  frames for Bi-directional predicted frames
  (called B frames).

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MPEG Simplified
Delta
Key
Delta
Temporal Compression
Delta
Key
Motion Picture Experts Group
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MPEG Sequence
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MPEG Sequence
I Frames
10
1
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MPEG Sequence
P Frames
10
7
4
1
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MPEG Sequence
B Frames
10
9
8
7
6
5
4
3
2
1
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MPEG Sequence
10
9
8
7
6
5
4
3
2
1
Sequence 1 x x 4 2 3 7 5 6 10
8 9
25
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Video Traffic Pattern
KeyFrame
KeyFrame
Delta Frames
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Video Effect of Delay
KeyFrame
KeyFrame
Delta Frames
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Video Playback Point
Typical Delivery
Playback Point
Transmission Time
Unless Its Too Late
Application Buffers Data to Ensure Consistency
Distribution of Deliveries in Time
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Compression Latency
lt45ms 200ms to 400ms 200ms to 500ms 400ms to
850ms
Motion JPEG MPEG-2 I Frame MPEG-2 I, P
Frames MPEG-2 I, B, P Frames

• Varies by vendor
• Network delay not included
• Low speed network can increase delay significantly

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Video Quality and Compression Data Rates
D1
MPEG-2 (IBP)
MPEG-2 (I)
Broadcast
Laser Disk
Motion JPEG
MPEG-2 (IP)
VHS
2
4
6
8
10
12
20
30
Bit Rate (Mbps)
27
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Another Look from Mpeg.org
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Motion JPEG vs. MPEG-2 Video Codecs
30K
25K
20K
MPEG-2
15K
Motion JPEG
10K
encoder/decoder2 ATM OC-3
encoder/decoder2 ATM OC-3
5K
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Video Conferencing Standards
H.320 Room Systems
ISDN
WAN
H.323 LAN Systems
IP
LAN
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Video Conferencing Standards
H.261
Video
G.711 G.722 G.728
Audio
ISDN H.320
T.120
Data
H.263 H.261
Video
G.711 G.723 G.722 G.728
LAN H.323
Audio
T.120
Data
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H.261/H.263 Compression

• Video conferencing specific
• Lower resolution picture
• Bandwidth optimization
• Similar to MPEG

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Audio Compression Standards
CompressRatio
BandwidthRequirement
Source BW
Method
G.721 G.722 CELP MPEG
2 1 3.54.6 1 13 1 311 1
32 Kbps 4864 Kbps 16 Kbps 64256 Kbps
64 Kbps 224 Kbps 64 Kbps 706 Kbps
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T.120 Data Conferencing

• File transfer
• Image transfer
• Applications plug in

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ISDN and LAN Conferencing Gateway
Switched ISDN
GW
H.320/H.323 Gateway
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Multipoint Conferencing
Switched ISDN
GW
MCU
Multipoint Control Unit
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Adding Conferencing over a WAN Data Network
Intranet Internet
Switched ISDN
Gatekeeper and Proxy
Gatekeeper and Proxy
GW
MCU
Multimedia Conference Manager
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Agenda

• Applications
• Technology
• Network Planning
• Examples

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Network Planning

• IP or ATM
• Quality of Service
• Bandwidth
• Delay and Jitter
• Multicast

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IP Frames or ATM Cells?
IP
ATM
Ethernet(s) FDDI ATM
Transport
ATM Only
RSVP IP Precedence
VBR, CBR
QoS
Assured thru Routers
Guaranteed by Switches
Bandwidth
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Bandwidth
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Bandwidth and Load
Video ConferencingMPEG-1/MPEG-2 Video on
Demand
128 Kbps 384 Kbps 1 Mbps 6 Mbps 128 Kbps 512
Kbps 1 Mbps
100 pps 100 pps 85 pps 500 pps 11 pps 44 pps 88
pps
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Delay and Jitter
Id like to talk about your proposal
What??!! I cant understand you!
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Multicast
IGMP
Video Server
IGMP
IGMP
IGMP
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Multicast with Pruning
IGMP
Video Server
IGMP
IGMP
IGMP
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Agenda

• Applications
• Technology
• Network Planning
• Examples

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Jefferson County Public Schools
IP/TV
IP/TV
IP/TV
IP/TV
IP/TV
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Broadcast VideoBT MediaNet
Content Servers
Web Control
Cisco 7513 Headend Router
Management
FDDI
Video Feed
Cisco 4700 Headend Router
Cisco LS1010 ATM Switch
PC-Based MPEG-1 Encoding
Ethernet
622 Mbps ATM
155 Mbps ATM
Client PCs with MPEG-1 Decoding
Cisco 4500 Client Routers
Ethernet
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Virginia Community College System
LS1010
ATM WAN
Cisco 7000
LS1010
Cisco 4700
Cell Mux
Cell Mux
LS1010
VTel
VTel
Cisco 4700
OC3c
Cell Mux
DS3
VTel
DS1
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Scottish Metropolitan Videoconferencing Network
St. Andrews
ATM Network
Aberdeen
Edinburgh
MCU
Glasgow
Motion JPEG
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Cisco Multimedia Training Network
H323 Station
P/GK
Proxy Gatekeeper
MCU
San Jose
384K
256K
1536K
Proxy Gatekeeper
Proxy Gatekeeper
Proxy Gatekeeper
P/GK
P/GK
P/GK
H323 Station
H323 Station
H323 Station
Irving
Salt Lake City
Denver
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Summary

• Applications
• Technology
• Video and Audio Compression
• Conferencing Standards
• Network Planning
• Example Networks