SWE 423: Multimedia Systems Chapter 2: Media and Data Streams

The Term Multimedia Multi Media Prefix From Latin “Multus” meaning numerous Media Root Plural form of the Latin word “Medium”. “Medium” is a noun meaning middle or center. Objective: Introduction to the terminology

The Term Media Media: A means to distribute and present information Text Graphics Pictures Voice Sound Music

Attributes of Media Perception Media Representation Media Storage Media Transmission Media Information Exchange Media Presentation Spaces and Presentation Values Presentation Dimensions Perception Media: Q: How do we perceive the data? What we see vs. what we hear Representation Media: Q: How do we encode the data? Text: ASCII. Picture: CEPT or CAPTAIN standard or the GKS graphics standard Audio: PCM Encoding (Pulse Code Modulation) & Linear quantization of 16bits per sampling value Image: JPEG Format Moving Picture: TV Standard, MPEG Presentation Media: Q: Which medium is used for output/input? Output: paper, computer monitors, speakers. Input: Keyboards, Cameras, Microphones Storage Media: Where is the media stored? Magnetic Tapes/disks or digital optical disks. Transmission Media: Q: Which medium is used to transmit data? Cables, radio towers, satellites, ether. Information Exchange Media: Q: Which data medium is used to exchange information between different locations? Paper, floppy disks, flash mem Presentation Spaces and Presentation Values: Visual vs. acoustic presentation space Presentation Dimensions: 2D: Monitors, 3D: Holography, stereophony, Time is another dimension. Discrete Media vs. Continuous Media (Correctness of data depends on a time condition.

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 Integration: Way different media will interact in a meaningful way.

Characterizing Data Streams Distributed networked multimedia systems transmit continuous and discrete data Data transmission characteristics: Asynchronous Synchronous Isochronous Source, Sink, packets Transmission modes available for an end to end delay in the transmission of a single packet. FDDI: Fiber Distributed Data Interface [up to 100MBPS)(FDDI2:Video and Audio in addition to data, FFDT: FDDI Full Duplex Technology (up to 200MBPS).

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. Periodically Regular e.g. MPEG Strongly Regular e.g. uncompressed audio/video

Variation of the Data Volume of Consecutive Information Units. Irregular e.g. JPEG

Connection between consecutive packets: Interrelated No gaps in between Maximal throughput and use of resources e.g. ISDN channel transmitting audio ISDN (Integrated Services Digital Network)

Connection between consecutive packets: Non-Interrelated Gaps between some packets e.g. DVI-PLV encoded streams over FDDI DVI-PLV (Production-level video) FDDI: Fiber Distributed Data Inetrface

Comparison

Information Units Logical Data Units E.g. Video Data Clips Scenes Images Regions Pixels