1. SCA3103 - Introduction to Multimedia
Semester 2 02/03
LECTURE 8 THE USES OF DIGITAL VIDEO IN MULTIMEDIA
Lecture 3: Video
Lecture 3

2. Objective 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

3. 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

4. Analog video Usage : television
Problems: colour blending, low clarity, high generation lost, difficult to edit

5. 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

6. Type of Analogue Video Signal
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 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)

7. 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

8. Video capture Technology and Playback Systems
The lecture for this part please refer note that will be given later…..

9. Digital Video Software
The lecture for this part please refer note that will be given later…..

10. 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

11. 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)

12. 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

13. 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 !

14. 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

15. 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.

16. 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

17. 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 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

18. 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

19. 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

20. 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
...
8, 16 or 24 bits
Video
information
Audio
information

21. SCA3103 - Introduction to Multimedia
Digital video editing
SCA Introduction to Multimedia
Semester 2 02/03
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
Lecture 3

22. SCA3103 - Introduction to Multimedia
Digital video editing
SCA Introduction to Multimedia
Semester 2 02/03
Digital video editing can be non-linear process
You can move sections around inside the computer and play those sections back in any order
Lecture 3

23. Consumer desktop video
Typified by the Apple iMac DV computer
IEEE 1394 or FireWire interface
Digital camcorders

24. 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

25. 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

26. 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

27. Advantages and Disadvantages of using video
Is expensive to produce
Requires extensive memory and storage
Requires special equipment
Does not effectively illustrate abstract concepts and static situations

28. 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

29. Next lecture...
We will look at how Animation can be used in multimedia applications