What is Multimedia?

Multimedia can have a many definitions these include:
Multimedia means that computer information can be represented through audio, video, and animation in addition to traditional media (i.e., text, graphics/drawings, and images).

General Definition
A good general working definition for this module is:
Multimedia is the field concerned with the computer controlled integration of text, graphics, drawings, still and moving images (Video), animation, audio, and any other media where every type of information can be represented, stored, transmitted and processed digitally.

Hypertext is a text which contains links to other texts.
The term was invented by Ted Nelson around 1965.

HyperMedia is not constrained to be text-based. It can include other media, e.g., graphics, images, and especially the continuous media – sound and video.

Example Hypermedia Applications
• The World Wide Web (WWW) is the best example of a hypermedia application.
• Powerpoint
• Adobe Acrobat
• Many Others

Multimedia Applications
• Examples of Multimedia Applications include:
• World Wide Web
• Multimedia Authoring, e.g. Adobe/Macromedia Director
• Hypermedia courseware
• Video-on-demand
• Interactive TV
• Computer Games
• Virtual reality
• Digital video editing and production systems
• Multimedia Database systems

Multimedia Application Definition
A Multimedia Application is an application which uses a collection of multiple media sources e.g. text, graphics, images, sound/audio, animation and/or video.

Multimedia Systems
A Multimedia System is a system capable of processing multimedia data and applications.
A Multimedia System is characterized by the processing, storage, generation, manipulation and rendition of Multimedia information.

Characteristics of a Multimedia System
A Multimedia system has four basic characteristics:
• Multimedia systems must be computer controlled.
• Multimedia systems are integrated.
• The information they handle must be represented digitally.
• The interface to the final presentation of media is usually interactive.


Challenges for Multimedia Systems
• Distributed Networks
• Temporal relationship between data
• Render different data at same time — continuously.
• Sequencing within the media – playing  frames in correct order/time frame in video
• Synchronisation — inter-media scheduling. E.g. Video and Audio — Lip synchronisation is clearly important for humans to watch playback of video and audio and even animation and audio.

Key Issues for Multimedia Systems
The key issues multimedia systems need to deal with here are:
• How to represent and store temporal information.
• How to strictly maintain the temporal relationships on play back/retrieval
• What processes are involved in the above.
• Data has to be represented digitally — Analog–Digital Conversion, Sampling etc.
• Large Data Requirements — bandwidth, storage, Data compression is usually mandatory.

Desirable Features for a Multimedia System
Given the above challenges the following feature a desirable (if not a prerequisite) for a Multimedia System:
• Very High Processing Power — needed to deal with large data processing and real time delivery of media.
• Multimedia Capable File System —needed to deliver real-time media — e.g. Video/Audio Streaming.
• Special Hardware/Software needed – e.g. RAID technology.
• Data Representations — File Formats that support multimedia should be easy to handle yet allow for compression/decompression in real-time.

Components of a Multimedia System
Now let us consider the Components (Hardware and Software) required for a multimedia system:
• Capture devices — Video Camera, Video Recorder, Audio Microphone, Keyboards, mice, graphics tablets, 3D input devices, tactile sensors, VR devices. Digitizing Hardware
• Storage Devices — Hard disks, CD-ROMs, DVD-ROM, etc
• Communication Networks — Local Networks, Intranets, Internet, Multimedia or other special high speed networks.
• Computer Systems — Multimedia Desktop machines,
• Workstations, MPEG/VIDEO/DSP Hardware
• Display Devices — CD-quality speakers, HDTV, SVGA, Hi-Resolution monitors, Colour printers etc.

Applications
Examples of Multimedia Applications include:
• World Wide Web
• Hypermedia courseware
• Video conferencing
• Video-on-demand
• Interactive TV
• Groupware
• Home shopping
• Games
• Virtual reality
• Digital video editing and production systems

A Brief Look at Multimedia Data:

Input and Format
Text and Static Data
• Source: keyboard, speech input, optical character recognition, data stored on disk.
• Stored and input character by character:
Storage of text is 1 byte per character (text or format character).
For other forms of data (e.g. Spreadsheet files). May store format as text (with formatting) others may use binary encoding.
• Format: Raw text or formatted text e.g HTML, Rich Text Format (RTF), Word or a program language source (C, Pascal, etc..
• Not temporal — BUT may have natural implied sequence e.g. HTML format sequence, Sequence of C program statements.
• Size Not significant w.r.t. other Multimedia data.
Graphics
• Format: constructed by the composition of primitive objects such as lines, polygons, circles, curves and arcs.
• Input: Graphics are usually generated by a graphics editor program (e.g. Illustrator) or automatically by a program (e.g. Postscript).
• Graphics are usually editable or revisable (unlike Images).
• Graphics input devices: keyboard (for text and cursor control), mouse, trackball or graphics tablet.
• Graphics standards : OpenGL, PHIGS, GKS
• Graphics files usually store the primitive assembly
• Do not take up a very high storage overhead.
Images
• Still pictures which (uncompressed) are represented as a bitmap (a grid of pixels).
• Input: digitally scanned photographs/pictures or direct from a digital camera.
• Input: May also be generated by programs “similar” to graphics or animation programs.
• Stored at 1 bit per pixel (Black and White), 8 Bits per pixel (Grey Scale, Colour Map) or 24 Bits per pixel (True Colour)
• Size: a 512x512 Grey scale image takes up 1/4 Mb, a 512x512 24 bit image takes 3/4 Mb with no compression.
• This overhead soon increases with image size — modern high digital camera 10+ Megapixels _ 29Mb uncompressed!
• Compression is commonly applied.
Audio
• Audio signals are continuous analog signals.
• Input: microphones and then digitised and stored
• CD Quality Audio requires 16-bit sampling at 44.1 KHz Even higher audiophile rates (e.g. 24-bit, 96 KHz)
• 1 Minute of Mono CD quality (uncompressed) audio requires 5 Mb.
• 1 Minute of Stereo CD quality (uncompressed) audio requires 10 Mb.
• Usually compressed (E.g. MP3, AAC, Flac, Ogg Vorbis).
Video
• Input: Analog Video is usually captured by a video camera and then digitised.
• There are a variety of video (analog and digital) formats
• Raw video can be regarded as being a series of single images. There are typically 25, 30 or 50 frames per second.
• E.g. A 512 × 512 size monochrome video images take 25 × 0.25 = 6.25Mb for a minute to store uncompressed.
• Typical PAL digital video (720 × 576 pixels per colour frame) ≈1.2 × 25 = 30Mb for a minute to store uncompressed.
• High Definition DVD (1440 ×1080 = 1.5 Megapixels per frame) ≈4:5 _ 25 = 112.5Mb for a minute to store uncompressed. (There are higher possible frame rates!)
• Digital video clearly needs to be compressed for most times