Transcript Lecture 3: Video

LECTURE 8
Lecture 3: Video
THE USES OF DIGITAL VIDEO IN
MULTIMEDIA
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Objective
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Analogue video
What is digital video?
Calculating the size of digital video
Compression techniques
Digital video formats
Video capture hardware
Digital video editing
Consumer desktop video
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Analogue video
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Video information that is stored using television video
signals, film, videotape or other non-computer media
Each frame is represented by a fluctuating voltage signal
known as an analogue wave form or composite video.
Composite analogue video has all the video
components: brightness, colour and synchronization
Then, combined into one signal for delivery
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Analog video
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Usage : television
Problems: colour blending, low clarity, high generation
lost, difficult to edit
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Type of Analogue Video Signal
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There are two main analogue video formats
 PAL and NTSC
PAL (Phase Alternate Line)
 standard television format used in the European, UK,
Australia and South Africa
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Consist 625 scan lines drawn every 1/25 second
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Type of Analogue Video Signal
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NTSC is the American and Japanese standard
 Consist of 525 scan lines drawn every 1/30 second
Television usually has a 4:3 aspect ratio
 For every 1 pixel down there are 1.333 pixels across
Aspect ration is the comparison of width to height for a
viewing area
Digital TV has an aspect ratio of 16:9 (wide screen)
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What is digital video?
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Digital video is the digitisation of analogue video signals
into numerical format
It creates the illusion of full motion by displaying a rapid
sequence of changing images on a display device.
Conversion from analogue to digital format requires the
use on an ADC (Analogue to Digital Converter)
A Digital to Analogue Converter (DAC) can be used to
output digital video on analogue equipment
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Video capture Technology and
Playback Systems
The lecture for this part please refer note
that will be given later…..
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Digital Video Software
The lecture for this part please refer note
that will be given later…..
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File Size Considerations
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Several elements determine the file size, in additional to
the length of the video. These including:
Frame rate
 Number of images displayed within a specified
amount of time to convey a sense of motion
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Usually measured in frames per second
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Standard video movie  30 fps, movie film  24 fps
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Video digital  at least 15 fps
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File Size Considerations
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Frame or Image size
 the width and height of each individual frae or image
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Determines the quality of the image displayed and the
processing involved to display that image
Standard full screen resolution is 640x480 pixels
Video screen display is one fourth the size of the full
window screen (320x240)
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File Size Considerations
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Color depth/Resolution
 Number of colors displayed on the screen at one time
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Ranging from 1 bit to 8 bit, 16 or 24 bit per pixel
Quality directly related to frame size, image size and
color depth.
Qualitiy also depends on content. Motion picture needs
higher frame rate
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Calculating the size
of digital video
File size = frame size * frame rate * Color Depth * time
Where:
• Frame size = image size ( width * height in pixels)
• Frame rate = frames per second
• Color depth = measured in bytes
• time = time in seconds
This does not include any sound data !
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Compression techniques
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Since the size of raw digital video is so prohibitively large
we need some means to compress the information
Video compression and decompression program, known
as Codecs
Lossy compression techniques cause some
information to be lost from the original image
 Redundant information
 Example: Image and video
 JPEG and MPEG
 Intraframe and Interframe
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Compression techniques
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Lossless compression techniques do not lose
information throughout the compression and
decompression process
 Example use in text images
 Exactly same before and after compression
 Technique is identify repeating words and assign
them a code.
 Decompression, the code would be changed back to
the actual word.
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Digital video formats
MPEG / MJPEG
Files with a .mpg extension
Apple QuickTime
Files with a .mov or .qt extension
Microsoft AVI
Files with a .avi extension
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MPEG video
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Named after the Moving Picture Experts Group who
devised the compression and file formats
There are a number of MPEG formats:
 MPEG-2 is used for digital TV broadcasts and DVDs
 MPEG-1 is a format used for low quality video
(generally displayed on computers)
 MPEG-1 Layer 3 is the popular encoding
mechanism for MP3 audio files (more on this later
in this course)
 MPEG-4 is a new format for multimedia presentations
Can require separate hardware to decode higher quality
MPEG video data
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MPEG compression example
A simple scene showing a car moving
across a desert landscape
Only the difference
between the current
and next frame needs
to be stored
This is called intraframe coding
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QuickTime
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Developed by Apple, Inc.
Primarily for playback
without any hardware
assistance
Can achieve compression
ratios of 25 to 200:1
The QuickTime format can
also store audio, graphics,
3D and text making it more
much versatile for
multimedia applications
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Microsoft AVI
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Audio Video Interleave format
Interleaving is a technique used to embed two or more
things into the same stream of information
In every chunk of information you will find some video
data and some audio data
8, 16
or 24
bits
001001010010010101010011110101...
001001010010010101010011110101...
...
001001010010010101010011110101...
001001010010010101010011110101...
Video
information
Audio
information
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Digital video editing
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Analogue tape editing is a linear process
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To find the section you want, you may have to forward
or rewind the video tape
To move a section to another place in the sequence
you have to either re-record the section onto another
tape or physically cut and splice the video tape
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Digital video editing
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Digital video editing can be non-linear process
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You can move sections around inside the computer
and play those sections back in any order
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Consumer desktop video
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Typified by the Apple iMac
DV computer
IEEE 1394 or FireWire
interface
Digital camcorders
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How audio can be used effectively
Example of uses for video
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Showing physical procedures. Some uses are:
 Installing a board in a PC
 Adjusting engine timing
Attracting and holding attention. Some uses are:
 Advertising products and services
 Teaching new skills to busy employees
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How audio can be used effectively
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Presenting scenarios. Some uses are:
 Training technicians to respond to equipment
malfunctions
 Demonstrating possible uses for a product
Analyzing motion . Some uses are:
 Body motion to improve athletic performance
 Traffic patterns for transportation planning
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Advantages and Disadvantages
of using video
Video adds visual impact to multimedia applications:
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Advantages
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Captures interest
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Increase retention
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Clarifies complex physical actions and relationships
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Can incorporate other media
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Advantages and Disadvantages
of using video
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Disadvantages
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Is expensive to produce
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Requires extensive memory and storage
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Requires special equipment
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Does not effectively illustrate abstract concepts and
static situations
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Summary
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Today we have seen how analogue video formats
are composed and how digital video can be used to
store these electronically
Digital video demands huge file sizes
• even before sound is added on!
Compression techniques help to reduce the file
sizes to more manageable levels
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Next lecture...
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We will look at how Animation can be
used in multimedia applications
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