08/03/02000 david bown msc cblt/multimedia 1 video and dvd
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08/03/02000David Bown MSc CBLT/Multimedia 1
Video and DVD
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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:Universal compatibility: MPEG files are
system independent. Greater compression ratiosGreater compression ratios than any
other format (up to 200:1). Highest qualityHighest 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