Video and DVD
08/03/02000 David Bown MSc CBLT/Multimedia 1
What is DVD?
DVD was the first distribution medium
designed for digital video.
Hence it originally stood for Digital Video
Disc.
Digital offers dramatic improvements in
transmission efficiency compared to
analogue video.
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Studio Quality Images
DVD now stands for Digital Versatile Disc.
It offers an optical (and audio) storage
medium with enormous capacity and
bandwidth compared to CD-ROM.
Standard specifications include MPEG-2
video which gives studio quality 740X480
pixel images (VHS tape: 320X240).
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Recordable DVD
DVD-R Recordable once, read on DVD-ROM.
DVD-RAM read and write to 2.6 GB DVD-
RAM Disc and read and write once to 3.9
GB DVD-R Discs.
DVD-Ram discs readable on DVD-R and
DVD-ROM drives.
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High Capacity
Full length films 133 minutes of MPEG-2.
Single layer discs: 4.7 Gbyte.
Dual-layer discs: 8.5 Gbyte.
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Double-sided DVDs
Double-sided dual layer discs with back to
back bonding.
By combining with Dual layer a massive
capacity of 17 Gbytes can be obtained.
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Data Storage on DVD
Like CD-ROMs data is recorded in spiral of tiny
pits.
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Capacity Gains over CD-ROM
DVDs obtain significantly more capacity by:
Shorter wavelength laser;
Smaller pits (0.4 micrometers v 1.1 on CD-
ROMS)
Denser track pitch (0.74 micrometers v 1.6 on
CD-ROMS)
Increased efficiency in channel encoding.
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Construction of DVD
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Variable Bit Rate
Average bit rate for
DVD is 4.7 mbs.
But the rate varies
between >3 to
10.07mbs.
This enables high
quality images to be
generated from
complex scenes.
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MPEGs
(Moving Pictures Expert Group)
Video standard for DVD, MPEG uses three types of
video frame:
I-Frames contains all spatial info of video frame.
These are used as the “hooks”, every scene
change requires a new I-Frame.
B-Frames (Highest compression).
P-Frames.
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MPEG Advantages
Universal compatibility: MPEG files are
system independent.
Greater compression ratios than any other
format (up to 200:1).
Highest quality compression does not lead
to sacrifice in quality.
MPEG delivers broadcast quality video.
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Advantages of DVD
Added features over Video tape.
Immediate scene access.
There are more than 5,600 movie and
music videos currently available.
Same size as CD but can store an entire
film.
DVD offers superior picture and sound.
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Future of DVD?
DVD or Sony‟s Phase-Change Rewritables
(PCR) disc or NEC (Betamax v VHS).
Hitachi propose a DVD-RAM disc with
phase-change technology that will be
retrospective to CD-ROM and DVD-ROM.
Blue lasers developed in Japan mean a laser
footprint even smaller than DVD can be
obtained.
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History of Video on the Web
Multimedia became commonplace back in
1992 with CD-ROMS.
But the Web has low bandwidth and cannot
cope easily with moving pictures.
TV uses “fat” cable infrastructure, Web uses
“thin” telephone infrastructure.
Moving images on the Web like “sucking a
bowling ball through a garden hose”.
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Video Compression
Temporal compression: frame by frame.
Spatial compression: deletes information
common to entire file and defines „areas‟
rather than pixels.
In addition, file size can be reduced by
cutting:
Colours
frame rate
audio quality.
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Hardware v Software Codecs
Hardware codecs are faster and require
fewer CPU resources.
Delivers high-quality results.
But are more expensive.
Software codecs are less expensive, e.g.
freeware versions.
Take long time to analyse and compress.
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DV Filmmaking
Digital Video (DV) was introduced to U.S.
consumers in 1994.
Digital Video is a high resolution video
format that stores, manipulates and relays
data like any other computer data.
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Benefits of DV
Excellent images, being digital the copy
quality is identical to the original.
Three separate signals for each colour
offering good colour reproduction.
Ability to use “Firewires” high speed
connections in and out of computers.
Portable and relatively inexpensive
cameras.
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„FireWire‟ - Wired for Speed
A high-speed serial bus cable designed by Apple
to provide cheap digital interface.
Based on the port found on Nintendo Gameboy.
Provides a transfer rate of 50 megabytes/sec
(Broadcast quality needs just 3.6)
It can link up to 63 devices.
Unlike SCSI no device IDs need to be set.
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Webmonkey Hints
Use a tripod.
Use tight close-ups.
Use quality resources.
Do not shoot very dark or light
backgrounds.
Capture rate no bigger than 320 x 240
pixels at 10 frames per second.
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The End
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