CGMB324: multimedia system design

CGMB324: MULTIMEDIA SYSTEM DESIGN

Chapter 10: Multimedia Hardware, Storage Devices, Software & Applications

Objectives

Upon completing this chapter, you should be able to:

understand the important requirements of a multimedia workstation

identify the common input and output technologies related to multimedia

discuss the concept related to optical storage media

identify important characteristics of a multimedia operating system

identify the common types of multimedia software and applications

Multimedia Hardware

Multimedia Workstation Requirements Processor – distribute the work among

different processors Bus – must have dedicated, synchronized

bus for continuous multimedia data Multimedia devices – for I/O of

multimedia data

Multimedia Hardware

Primary storage – for copying operation Secondary storage – to balance between

high storage density, low access time Operating system – distinguish between

processes for continuous and discrete computation

Multimedia Hardware

Input / output technologies Pen input Video and image display systems Print output Image scanners Digital voice and audio capture Video images and animation Digital camera

Multimedia Storage Requirements

MM systems require storage for large capacity objects such as video, audio, animation and images.

Depending on the compression scheme, video bandwidth requirements range from 1.5 Mbit/s (MPEG-1) to 10 Mbit/s (MPEG-2) and up to 1 Gbit/s (HDTV)!!

Depending on the fidelity and compression, audio may consume from 8 Kb/s all the way up to 384 Kb/s.

In applications that require multiple multimedia streams, these numbers increase accordingly.


Some of the major distinguishing characteristics of multimedia objects are:

multimedia objects are large (large file sizes),

multimedia streams have stringent real-time requirements,

multimedia streams represent long and fairly constant (predictable) loads,

multimedia streams usually have high bandwidth requirements,

multimedia objects tend to exhibit sequential access patterns within a given medium.


Multimedia objects have real-time playback and, in many cases, similar recording requirements.

Video is somewhat scalable in the sense that its frame rate, and to a certain extent, its window size, may be varied to compensate for response time fluctuations without significantly perceptible adverse effects.

Audio on the other hand, has stringent timing requirements and needs virtually constant playback speed for acceptable quality.


The file systems of earlier operating systems were designed to handle bursty traffic with no real-time requirements, and they usually have rather poor throughput for continuous load.

Indexing and retrieval of multimedia objects poses some very different and demanding requirements for navigation on database systems;

e.g. multimedia databases need to support searches by media content, such as video clips and image attributes, on top of processing the traditional text-based queries.

There is still much work being done on this.


Mass storage devices are required to overcome the high demand for storage space for multimedia systems.

Among the mass storage devices, optical and magnetic media technology are some of the cheapest solutions as compared to internal storage devices like DRAM, SDRAM etc.

Usage of Magnetic Media In Multimedia

Multimedia Objects Volatile Objects – audio and video input.

They are sometimes not retrieved from storage but directly captured from the source.

Nonvolatile Objects – stored in a storage device. Two issues arises: Capacity Transfer Speed / Bandwidth

Object TypeStorage Size /

Bandwidth per sec

Text 2.5KB per page

Binary Image Compressed G31D 50KB-100 KB

Fax G3 1D Image 50KB-100 KB

Binary Image Uncompressed 500K-1MBVideo at 320 X 240 resolution, 16 bit colour, 5 fps 768 KBVideo at 320 X 240 resolution, 8 bit colour, 30 fps 2-3MBVideo at 320 X 240 resolution, 16 bit colour, 20 fps 3.1MBVideo at 640 X 480 resolution, 24 bit colour, 30 fps 27.64MB

Audio at 8KHz, 8 bits sample, mono 8KB

Audio at 8KHz, 8 bits sample, stereo 16KB

Audio at 44.1KHz, 16 bits sample, stereo 176KB

Note the difference between the requirements of various multimedia objects



A/V (Audio/Video) Ready Magnetic Drive Temporal requirements of some

multimedia objects for sustained delivery had created a need for a device with guaranteed delivery.

The A/V ready drive was developed to address this need.


Features of A/V ready drive: Multi Segmented Caching – different

cache for different objects Write Behind Caching and Write

Coalescing – data to be written is buffered in cache first, and coalesces (blends) multiple write requests in a single disk revolution.

Tagged Command Queuing – tagging I/O request and queue them to reduce latencies.


Fast ECC (Error Correcting Codes) – auto-correcting soft errors.

Guaranteed minimum sustained rate: 3 Mbytes/sec

Fast Drive Speed (at least 5400 rpm) Synchronized Spindles – Supports RAID

Configurations

Optical Storage Media

General Concepts of Optical Storage Media

The optical technology is based on a light source A sharply focused laser beam is directed onto

the surface of a spinning disk Physical variations in the surface (pits and

landings) are arranged in concentric tracks of the disk

The pits and landings deflect the focused beam toward an optical receiver to signify a 1 or disperse the beam away to signify a 0

Optical storage is normally read-only

General Concepts of Optical Storage Media

Locating a specific address involves moving the head to a general area adjusting the rotation speed reading the address making minor adjustment to find and

access the specific sector

Review of Optical Storage Media CD-DA - Compact Disk Digital Audio

Stores digitized audio information (1982) CD-ROM - Compact Disk Read-Only Memory

Stores computer data (1985) Later became the High Sierra format (ISO9660)

CD-I - Compact Disk Interactive Stores audio, video, graphics, text and machine code on

CD-ROM (1986) DVI - Digital Video Interactive

Stores digitized, compressed representation of audio/video information on CD (1987)

CD-XA – CD eXtended Architecture Contains Multiple tracks differentiated by mode (1988)

WORM - Write-Once Read-Many A disk which is more easily written than CD (1990s)

Review of Optical Storage Media Erasable Optical Disk

Optical disk that can be easily erased and rewritten (1990s) DVD – Digital Video/Versatile Disk (1996)

A single-layer DVD can store 4.7 GB (4.38 GiB), which is around seven times as much as a standard CD-ROM.

BD – Blu-ray disc (Blu-ray Disc Association BDA) next-generation format for high-definition video and high-density

data. A single-layer disc can fit 23.3, 25, or 27 GB (enough for

approximately four hours of high-definition video with audio) supports 25GB for one layer, 50GB for two and 100GB for four,

HD-DVD (Toshiba) A single layer capacity of 15 GB and a dual-layer capacity of 30 GB Triple-layer disc is in development, which would offer 45GB of

storage.

Optical Storage Media CD-ROM Based on laser beam (780nm) reflection, focused at 1m

area 120mm diameter, 1.2mm thickness, 15 mm hole track-to-track spacing 1.6 microns Record-able width 32.55 mm number of tracks 32,550/1.6 = 20,344 tracks are arranged in a spiral storage capacity about 774.57 MBytes (unformatted) Some CD-ROMs have a formatted storage capacity of up to

870 MB, due to writing in the ‘lead-in’ / ‘lead out’ area of the disc

Optical Storage Media CD-ROM The CD-ROM is derived from the original CD audio music

disc. Because audio has a constant data rate, e.g. 44100

samples per second, the datarate you get when reading the disc has to be constant as well.

A typical audio CD spins at about 500 rpm when the laser is at the middle (center) of the disc and slows to about 250 rpm when reading the outer area of the disc.

This is because the laser reads a fixed number of centimetres of data track each second (CLV – Constant Linear Velocity), and this data is packed the same way whether at the middle or edge of the disc.

A CD audio disc delivers about 150 KB/s (1x speed). CLV is used for drives under 12x usually.

Optical Storage Media CD-ROM Now, with fast CD-ROM speeds these days (e.g. 40x, 50x),

reading data using CLV would require changing speeds between 20,000 rpm at the center of the disc and 10,000 rpm at the edge.

This requires too much power when searching back and forth on a disc for a file.

So, since it isn’t really crucial what speed data (unlike music) is read from a CD these days, CD-ROMs use CAV (Constant Angular Velocity).

This means the disc spins at a fixed rate and the reading data rate varies. So, if the speed was fixed at 10,000 rpm, it would only deliver 40x speed at the outer edge (more data there) and 20x near the center (less data).

This is why data that is regularly accessed (like in certain games) is usually placed at the edge of the disc, to ensure it’s read as fast as possible.

Optical Storage Media CD-ROM

Three major advantages Information storage capacity is large It can be mass-replicated cheaply It is removable

Disadvantages Read-only and cannot be updated Longer access time, typically half a second

Optical Storage Media Erasable Optical Disk Can be repeatedly written and overwritten Uses magneto-optical technology

A laser beam and magnetic field is used to record and erase information

Laser beam heats a spot on the medium While it is still hot, a magnetic field changes the

orientation of that spot Uses constant angular velocity (CAV) Principal advantages

High capacity - 650 Mbytes Portability - Removable Reliability

Optical Storage Media Digital Video Disk (DVD) made from a 0.6 mm thick disc of polycarbonate plastic

coated with a much thinner reflective layer of aluminium or gold.

Two such discs are glued together to form a 1.2 mm disc that can be designed to be read from one side (single sided) or both sides (double sided).

can be used for data storage, including movies with high video and sound quality.

DVDs resemble compact discs as their physical dimensions are the same (12 cm or occasionally 8 cm in diameter) but they are encoded in a different format and at a much higher density.

A single-layer DVD can store 4.7 GB (4.38 GiB), which is around seven times as much as a standard CD-ROM.

DVD format is 47 % more efficient with respect to CD-ROM

Multimedia Operating Systems

Multimedia Operating Systems Notion of real time

Real Time process = process which delivers the results of the processing in a given time span.

Dead lines Divided into soft deadline and hard deadline. Soft deadline can be violated without any adverse effect

but not hard deadlines!! Real time features:

Predictably fast response to critical events High degree of resource utilization Stability under transient (temporary) load


MM systems have a different set of real-time requirements: Fault tolerance requirements are less strict Some multimedia applications can afford to

miss a deadline without any severe failure All time critical processing are periodic

rather than sporadic (irregular instances)


Resource Management1. Resources

Can be active or passive Exclusive or shared Single or multiple instance

2. Multimedia requirements Throughput determined by the needed data rate Local and global (end-to-end) delay Jitter – maximum variance Reliability – error detection and correction (QoS –

quality of service)


Resource Management3. Components and phases

Client makes a reservation request to the resource manager component.

Resource manager will see whether the request can be guaranteed or not

4. Allocation schemes Pessimistic approach (reservations for worst case) Optimistic approach (for average workload)


Process Management Real time processing requirements for scheduling

multimedia tasks two conflicting goals must be satisfied

Uncritical process should not starve Time critical process should never be subject to priority

inversion.

File System Management MM systems tends to have more continuous data than

discrete data, which are different in terms of: Real time characteristics (time dependent delivery) Large file size Multiple data streams


Other OS issues IPC (inter-process

communication) and synchronization

Memory management Device management

Multimedia Software & Applications

Multimedia Software

Software for Media Composition Text and Graphics Editors Image Editors Animation Editors Sound Editors Video Editors Editors often allow you create media as

well, but not always. If not, you will need a separate application to create media, like for video capture.

Multimedia Software

Software for Media Integration Multimedia Editors Hypermedia / Hypertext Editors Authoring Tools

Multimedia Applications

Interactive Conversational – video conferencing, video

phone, Computer supported cooperative work (CSCW).

Messaging Service. E.g. MIME (Multipurpose Internet Mail Extensions) – send/receive multimedia files via e-mail

Retrieval Service – Video Server, WWW, Gopher Tele-action Service – Tele-robotics with

kinesthetic feedback Tele-operation Service –remote education,

Tele-office, Tele-collaboration, telemedicine


Distribution Pay-per-view – similar to cable service Near Video on Demand (Near VoD) –

multichannel broadcast + deferred airing True Video on Demand (VoD) – e.g.

interactive TV, Cyber Vision


Media Consumption Viewing Multimedia Documents –browsing

or detailed media consumption Electronic Books, Proceedings and

Newspapers Info Kiosks Tele-shopping


Media Entertainment Virtual Reality (VR) Interactive Video - interactive TV, VoD. Interactive Audio - CD on Demand Games – Tele-games


Trends From reengineering to establishing new

application domains From single PC user to multi-user or

personalized environment Application becomes less local, more distributed Media Consumption mode from passive to

active interaction From unidirectional to bi-directional information

flow Technical improvements improve productivity

through better collaboration and visualization.

List of References

http://en.wikipedia.org/wiki/Blu-ray_Disc