Transcript Document 7371806

Digital Video Class
Spring 2006 Internet2
Member Meeting
Larry Amiot
Northwestern University
[email protected]
And
Dave Devereaux-Weber
University of Wisconsin at Madison
[email protected]
Agenda
• Analog/Digital Video
• Digital Video ABCs
• Digital Video Applications
• Break
• Digital Academic Television Network
• Program Guide
• Question and Answer
• Demonstrations
Video – Analog and Digital
• Analog
• Original broadcast television was black &
white
• 262 ½ odd and 262 ½ even lines (fields)
are interlaced to conserve bandwidth
• 60 fields per second
• 15,750 lines per second
National Television System
Committee (NTSC)
• A committee appointed by the Federal
Communications Commission
• Set standards for US television
Composite Video
• Video and synchronizing pulses on the
same wire
• 1 volt peak-to-peak
• 100 IRE (Institute of Radio Engineers) units of video
• 40 IRE units of sync
NTSC does Color
• Backwards compatible with B&W
• Color information added with a subcarrier
• Saturation represented by subcarrier
amplitude
• Hue represented by subcarrier phase
RGB
• 3 connections: red, green & blue
• Full bandwidth, full resolution, full detail
Digital Video
• Over the air in the US, the standards body
for digital is the Advanced Television
Systems Committee http://www.atsc.org/
• One family of digital video encoders &
decoders (codecs) is MPEG
• Named from the Moving Pictures Experts
Group
• http://www.mpeg.org/
Digital Video
• DVB is a standard for digital vide
broadcasting
• Originally European, now used around the
world
• http://www.dvb.org
Digital Video
• DV
• Standard used by Sony, Avid, Apple
Microsoft, others
• (Doesn’t use MPEG)
IP, Codecs & Business Model
• Codecs include Intellectual Property (IP)
• IP often protected by patents
• Need to license patented IP
IP, Codecs & Business Model
• Windows Media (Microsoft), user cost is free,
•
•
subsidized by sale of Microsoft software
Quicktime (Apple Computer), user cost is
free, subsidized by sale of Apple Computers
Real Media player is free, server is paid, no
hardware or software to subsidize
IP, Codecs & Business Model
• License for MPEG-2 Player is $2.50 each
• MPEG-2 codec not included with Windows
Media or Quicktime
• MPEG-4 codec included in Windows Media
& Quicktime
IP, Codecs & Business Model
• VideoLAN http://videolan.org/ is free,
open source
• Has codecs with IP issues (MPEG-2)
• Does not pay a license fee for IP
• Use of VideoLAN may carry IP risk.
Digital Video ABCs
Understanding Digital Video Quality
• Three important factors
– Image resolution
– Compression
– Bit rate of the compressed video stream
Image Resolution
Image Resolution
• What is a pixel?
– Tiny square or rectangular, colored picture
elements on a LCD, plasma, DLP, or projection
LCD monitor
– Tiny round, color phosphor dots on a CRT
– A value (e.g. 8 bit or 24 bit) defining color
and luminescence
Image Resolution
• What is resolution?
– The number of pixels on an image or on a
frame of a video
– The more pixels, the better the resolution
– Usually expressed as the horizontal pixels
times the vertical resolution
• E.g. 720x480
Image Resolution
• Interlaced Scan
– Draw odd lines first, then the even lines
– Full motion video requires frames every 1/60
of a second
– The way NTSC does it
• Progressive scan
– Drawn top to bottom
– Full motion video is 30 frames per second
Image Resolution
• Standard Definition Television (SDTV)
– A set of digital television standards with 480
lines of resolution
– At least as good if not better than NTSC
– A subset of the Digital TeleVision standards
(DTV)
– All SDTV formats are interlaced
Image Resolution
• DTV standards
– ATCS is the standard in North America
– All use MPEG2 compression
– 18 digital formats covering:
• Standard definition
• Enhanced definition
• High definition
DTV Formats
High Definition TV
1. 1920 x 1080 16:9 24p
2. 1920 x 1080 16:9 30p
3. 1920 x 1080 16:9 30i*
4. 1280 x 720 16:9 24p
5. 1280 x 720 16:9 30p
6. 1280 x 720 16:9 60p*
Square
Square
Square
Square
Square
Square
10.
11.
12.
13.
14.
15.
704
704
704
640
640
640
x
x
x
x
x
x
480
480
480
480
480
480
4:3
4:3
4:3
4:3
4:3
4:3
24p
30p
60p*
24p
30p
60p
Rectangle
Rectangle
Rectangle
Square
Square
Square
Standard Definition TV- 480i
Enhanced Definition TV - 480p
16. 704 x 480 16:9 30i Rectangle
7. 704 x 480 16:9 24p Rectangle 17. 704 x 480 4:3 30i*Rectangle
8. 704 x 480 16:9 30p Rectangle 18. 640 x 480 4:3 30i Square
9. 704 x 480 16:9 60p* Rectangle
* most popular formats
Image Resolution
• CIF
– A video format widely used in
videoconferencing
– Common Intermediate Format (CIF)
QCIF - Quarter CIF (resolution 176x144)
SQCIF - Sub quarter CIF (resolution 128x96)
CIFFull CIF (resolution (352x288)
4CIF - 4 x CIF (resolution 704x576)
16CIF - 16 x CIF (resolution 1408x1152)
Compression
Compression
• Spatial Redundancy
– Takes advantage of identical picture elements within a
video frame
• Temporal Redundancy
– Takes advantage of identical picture elements
between frames
– Takes advantage of the movement of identical picture
elements between frames (motion vector)
• Psychovisual Redundancy
– Takes advantage of human eyes limited response to
fine spatial detail
Compression
• Lossless compression
– You can take the compressed data and uncompress it
to obtain an identical copy of the original
uncompressed data
– E.g. TIFF image
• Lossy compression
– You can not get the original data by uncompressing
– Allows much greater compression than lossless
compression
– E.g. MPEG
JPEG Compression
• A standard of the Joint Photographic Experts
•
•
•
•
Group
A lossy compression technique
Handles still images
The degree of lossiness can be varied by
adjusting compression parameters- trade quality
for file size
You can also trade off decoding speed against
image quality
JPEG Compression
• A 24 bit per pixel color scheme as compared to
•
•
GIF which is 8 bit
Can easily provide 20:1 compression of full-color
data (about four times better than GIF but
slower to decode)
Motion JPEG (M-JPEG) provides a video stream
– but it is not a standard
– Does not use inter frame compression
MPEG Compression
• MPEG is recognized standard for motion
picture compression
– Uses many of the same techniques as JPEG,
but adds inter-frame compression
– Compresses by about a factor of 3 better than
M-JPEG except at very low frame rates
– Takes more computation than JPEG to
compress
– Difficult to edit on a frame by frame basis
Intra Frame EncodingI Frames
• Every frame is encoded separately
• Easy to edit
• Fast to decode
• Lost frame produces small artifact
I I I I I
I I
I
Inter Frame EncodingI and P Frames
• Forward predicted from the last I-frame or P•
•
•
•
•
•
frame
Better compression
A little harder to decode
More difficult to edit
More artifacts if a frame is lost
Buffering of previous frame required
Frames sent in order
Inter Frame EncodingI, P, and B Frames
• B-frames are both, forward predicted and
•
•
•
•
•
•
backward predicted from the last/next I-frame
or P-frame
Best compression
Hardest to decode
Most difficult to edit
More artifacts with lost frames
More buffering required
Frames not sent in order
Sent IPBBBPBBB
So what’s a GOP?
• A set of frames, typically between 4 and
20, is called a Group Of Pictures
• At most one frame in the GOP can contain
a reference to a frame in another GOP
• Some GOPs do not reference any other
GOP
– E.g. IBBPBBP
MPEG Compression
• Three defined standards
– MPEG1
– MPEG2
– MPEG4
MPEG1
• Optimized to work at video resolutions of
352x240 pixels at 30 frames/sec and 1.5
Mbps
• May go as high as 4095x4095 at 60
frames/sec
• Progressive scan only
MPEG2
• Target bit-rate was raised to between 4 and 9
•
•
•
Mbps
Commonly used at 720x480 resolution video at
30 frames/sec, at bit-rates up to 15 Mbps
Also used for HDTV resolution of 1920x1080
pixels at 30 frame/sec, at a bit-rate of up to 80
Mbps
Can do interlaced
MPEG4
• Originally optimized for very low bit rate
communication at rates less than 64 Kbps
• Currently used in videoconferencing for
HD at speeds up to 4 Mbps
Videoconferencing Video
H.323-based Videoconferencing
• An International Telecommunications
Union (ITU) umbrella standard for
videoconferencing across IP networks
• Includes protocols for:
– Video (i.e. H.261, H.263, and H.264)
– Audio (G711, G722, etc)
– Control (H.245, etc)
H.261 Compression
• Part of the H.323 videoconferencing set of
•
•
•
standards
Originally for two way communication over ISDN
lines- now over the Internet
Supports intra and inter frame compression
Resolutions supported
– QCIF(144x176 pixels)
– CIF(288x352)
H.263 Compression
• Part of the H.323 videoconferencing set of
•
•
standards
Based on H.261 but with enhancements to
improve video quality
Resolutions supported
–
–
–
–
–
QCIF(144x176)
CIF(288x352)
SQCIF (128x96)
4CIF (704x576)
16CIF(1408x1152)
H.264 Compression
• Part of the H.323 videoconferencing set of standards
• H.264, MPEG4, & AVC (Advanced Video Coding) are
•
•
•
related codecs for achieving very high compression
Adds B frames to compression
Ultra-efficient technology that gives you excellent
results across a broad range of bandwidths, from 3G for
mobile devices to iChat AV for video conferencing to HD
for broadcast and DVD
Used in QuickTime 7
H.264 Compression
• H.264 delivers the same quality as MPEG-2 at a
•
•
third to half the data rate
H.264 Part 10 delivers up to four times the
frame size of MPEG-4 Part 2 at the same data
rate
Resolutions supported
– SQCIF (128x96)
– 720p HD (1280x720)
– 1080 HD (1920x1088)
DV and MiniDV
• A format developed by several manufacturers for
•
•
•
•
•
recording on cassettes
500 line horizontal resolution
Utilizes the IEEE 1394 digital interface (Firewire)
Bit rate of 25 Mbps
The sampled video is compressed using a
Discrete Cosine Transform (DCT), the same sort
of compression used in motion-JPEG
5:1 intraframe compression only
Bit Rate of Stream
Bit Rate
• The quality of the video is directly related
to the bit rate of the stream
• Low compression streams require more
bandwidth
• Many codecs dynamically adjust the
quality (compression) according to the
amount of bits that are produced
Bit Rate
• Variable bit rate
– Number of bits produced by the codec and sent varies
according to the redundancy and motion being
compressed at any moment
• Fixed bit rate
– Bits to be transferred are buffered
– If the codec starts producing information faster than
the buffering can handle, feedback to the codec
reduces the quality (compression) and thus the
number of bits produced
Bit Rate
• The quantization (Q) level of an MPEG stream is
•
•
•
•
a measure of the amount of data the encoder
throws away to bring the bit rate down
Higher Q values mean the encoder threw away a
lot of data, implying a low bit rate, but also low
visual quality
A low Q level implies a high bit rate, and high
visual fidelity
You can keep a constant bit rate by varying the
Q level
Alternatively, you can keep a constant Q level
and allow the bit rate to vary
Compression Trade Offs
High Compression
Less video quality
More buffering required
More latency
Less bandwidth required
More complex hardware
Less storage required
More susceptible to
packet loss
More difficult to edit
Low Compression
Better video quality
Less buffering required
Less latency
More bandwidth required
Less complex hardware
More storage required
Less susceptible to packet
loss
Less difficult to edit
High Definition Video
Broadcast High Definition TV
• Breathtaking quality on home monitors
– Plasma
– LCD and projection LCD
– Projection DLP
• Several carrier types
– Through the air
– Cable
– Satellite dish
• More and more HD programming becoming
•
available
Downside- watch too much television!
High Definition Video
• Two High Definition Formats
– 720p
• 1280x720
• Progressive scan
• Equivalent to 9CIF
– 1080i
• 1920x1080
• Interlaced scan
– Both 16x9 aspect ration compared to 4x3 of
SDTV
High Definition Video
• Uncompressed 1080i HD
•
1920x1080x24x30 ~ 1.5 Gbps
HDV
– Defined by four companies, Canon Inc., Sharp
Corporation, Sony Corporation, and Victor Company
of Japan, Limited (JVC)
– Idea is to store high-def MPEG-2 video on standard
DV media (DV or Mini DV cassette tape), and stream
it across standard FireWire / IEEE 1394 interfaces
High Definition Video
• HDV
– The format supports MPEG-2 compressed
video at two 16:9 resolutions:
• 720p (1280 x 720, progressive), at approximately
19 Mbps data rate
• 1080i (1440 x 1080, interlaced), at approximately
25 Mbps data rate- assumes a pixel aspect ratio of
1.33
High Definition Videoconferencing
H.323-based Videoconferencing
• Compression/decompression architectures
– Initially blurred and murky H.261 codecs
– Major use today is H.263
– Beginning to see H.264 (MPEG4)
• Bandwidth requirements have been low
(typically 1 Mbps or less)
H.323-based Videoconferencing
• Resolutions have been limited
– Typically CIF (352x288)
– Recent use of 4CIF (704x576 )- e.g. the
Gigaconference requiring bandwidths of 1 to 4
Mbps
• Aspect ratio of 4x3
• Several audio algorithms, but typically low
quality at 64 Kbps
High Definition H.323-based
Videoconferencing
• High definition videoconferencing is
becoming available
• H.323-based high definition video and
audio provides the quality necessary for
media rich collaboration
• Being standards-based, it offers
– User simplicity
– Promise of interoperability with other nonhigh definition H.323 systems
LifeSize H.323-Based Room Unit
• Produces 720p high definition video
• Utilizing H.264 codec
• 16x9 aspect ratio
• 9CIF quality
• 1 Mbps bandwidth (can go at 2 Mbps
point to point)
LifeSize H.323-Based Room Unit
• Built-in 4 port MCU
• Good acoustical quality
– omni-directional architecture
– circular array of 16 microphones
– 100 Hz up to 22 kHz bandwidth
• High definition camera with 70 degree
field of view
What Are The HD Driving Forces?
•
•
•
•
•
•
•
Do you need high definition resolution?
How important is audio quality?
Is aspect ratio important
Do you have sufficient bandwidth?
Do you need two way interaction
(conferencing)?
Is H.323 interoperability important?
What can you afford?
Other High Quality Video Options
• MPEG2
– VBrick, StarValley, etc
– High quality video in the 7 to 16 Mbps range
– Used at Northwestern for remote venues
• DVTS
– Lot of work being done in the Big Video
project
– Transports digital video over IP at 30 Mbps
– HDV over DVTS becoming available
Other High Quality Video Options
• Access Grid high definition experiments
• Microsoft ConferenceXP
– MPEG4 compressed high definition
DV Guide
Demonstrations
Composite
Video
Capture Card
DVD
Player
Speaker
MPEG2 stream
Display
VideoLAN
Client
VideoLAN
Client
VideoLAN MPEG2 Stream
Speaker
MPEG2 stream
DVD
Display
VideoLAN
Client
VideoLAN
Client
VideoLAN MPEG2 Stream
Speaker
Composite
Video/Audio
DVD
Player
7 Mbps (max)
MPEG2 stream
StarValley
Encoder
Display
VideoLAN
Client
StarValley MPEG2 Stream
Speaker
Firewire Stream
30 Mbps DVTS
stream
DV
Camera
Display
DVTS Client
(encode)
DVTS Client
(decode)
DVTS Stream
Speaker
Firewire
Camera
30 Mbps DVTS
stream
Canopus
A/D
Composite Video
Display
DVTS Client
(encode)
DVTS Client
(decode)
DVTS Stream
Speaker
Firewire
Audio/video
MPEG2 stream
HDV
Camera
Display
VideoLAN
Client
VideoLAN
Client
VideoLAN MPEG2 Stream
URLs
• DV Guide
http://db.arts.usf.edu/dvguide/default.asp
• VideoLAN
http://www.videolan.org/
• DVTS
http://www.sfc.wide.ad.jp/DVTS/