SWE 423: Multimedia Systems

Chapter 2: Media and Data Streams

The Term Multimedia

• Multi– Prefix– From Latin “Multus” meaning numerous

• Media– Root– Plural form of the Latin word “Medium”.– “Medium” is a noun meaning middle or center.

The Term Media

• Media: A means to distribute and present information– Text– Graphics– Pictures– Voice– Sound– Music

Attributes of Media

• Perception Media• Representation Media• Presentation Media• Storage Media• Transmission Media• Information Exchange Media• Presentation Spaces and Presentation Values• Presentation Dimensions

Key Properties of a Multimedia System

• Discrete and continuous media– Support of one type does not constitute

multimedia (according to authors)

• Independent media– Unlike video, one can have more than one type.

• Computer-controlled systems– Video recorder is not sufficient

• Integration

Characterizing Data Streams

• Distributed networked multimedia systems transmit continuous and discrete data

• Data transmission characteristics: – Asynchronous– Synchronous– Isochronous

Asynchronous Transmission

• The sender and the receiver do not need to coordinate before data can be transmitted.– Two independent clocks (one at the sender and

the other at the receiver) determine the start of each bit (bit synchronization)

Synchronous Transmission

• The beginning of transmission may only take place at well-defined times, matching a clocking signal that runs the synchronism with that of the receiver.

Isochronous Transmission

• The time interval separating any two corresponding transitions is equal to the unit interval or to a multiple of the unit interval.– Transmission rate “guaranteed” and jitter is

minimized.

• Significant instants of two or more sequential signals have a constant phase relationship.

Characterizing Continuous Data Streams

• This is in relation to audio and video transmission– Strongly and Weakly Periodic Data Streams– Variation of the data volume of consecutive

information units.– Interrelationship of consecutive packets.

Strongly Periodic Data Stream

• Constant time interval

• Minimum jitter

• e.g. PCM encoded voice in telephone systems

Weakly Periodic Data Stream

• Duration of time intervals between neighboring packets is a function with finite period duration.

• Time intervals between neighboring packets is not constant.

Non-Periodic Data Streams

• Other possibilities– e.g. mouse movement on white boards of the screen in

video conferences

Variation of the Data Volume of Consecutive Information Units.

Strongly Regulare.g. uncompressedaudio/video

Periodically Regulare.g. MPEG

Variation of the Data Volume of Consecutive Information Units.

Irregulare.g. JPEG

Connection between consecutive packets: Interrelated

• No gaps in between

• Maximal throughput and use of resources– e.g. ISDN channel transmitting audio

Connection between consecutive packets: Non-Interrelated

• Gaps between some packets– e.g. DVI-PLV encoded streams over FDDI

Comparison

Information Units

• Logical Data Units– E.g. Video Data

• Clips

• Scenes

• Images

• Regions

• Pixels