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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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Digital Video Software

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

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Next lecture...

We will look at how Animation can be used in multimedia applications