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Lecture 3: VideoLECTURE 8LECTURE 8
THE USES OF DIGITAL VIDEO IN THE USES OF DIGITAL VIDEO IN MULTIMEDIAMULTIMEDIA
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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
Objective
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Analogue video
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
Usage : television
Problems: colour blending, low clarity, high generation lost, difficult to edit
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Type of Analogue Video Signal
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
Consist 625 scan lines drawn every 1/25 second
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Type of Analogue Video Signal
NTSC is the American and Japanese standardConsist 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? 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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File Size Considerations 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
Usually measured in frames per second
Standard video movie 30 fps, movie film 24 fps
Video digital at least 15 fps
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File Size Considerations Frame or Image size
the width and height of each individual frae or image
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 Color depth/Resolution
Number of colors displayed on the screen at one time
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 sizeof digital video
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 !This does not include any sound data !
File size = frame size * frame rate * Color Depth * time
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Compression techniques 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 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 / MJPEGFiles with a .mpg extension
Apple QuickTimeFiles with a .mov or .qt extension
Microsoft AVIFiles with a .avi extension
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MPEG video
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 DVDsMPEG-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
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 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
001001010010010101010011110101...001001010010010101010011110101...
...001001010010010101010011110101...001001010010010101010011110101...
Videoinformation
Audioinformation
8, 16 or 24
bits
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Digital video editing
Analogue tape editing is a linear process
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
Digital video editing can be non-linear process
You can move sections around inside the computer and play those sections back in any order
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Consumer desktop video
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
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
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:
Advantages
Captures interest
Increase retention
Clarifies complex physical actions and relationships
Can incorporate other media
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Advantages and Disadvantages of using video
Disadvantages
Is expensive to produce
Requires extensive memory and storage
Requires special equipment
Does not effectively illustrate abstract concepts and static situations
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Summary
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