Multimedia Systems. Lehrstuhl für Informatik IV RWTH Aachen. Prof. Dr. Otto Spaniol Dr. rer. nat. Dirk Thißen

Transcription

1 Multimedia Systems Lehrstuhl für Informatik IV RWTH Aachen Prof. Dr. Otto Spaniol Dr. rer. nat. Dirk Thißen Page 1

2 Organization Lehrstuhl für Informatik 4 Lecture Lecture takes place on Thursday, 10:00 11:30 and 13:15-14:45 The lecture is planned with 3 hours / week Not each date is needed, some are skipped First lecture dates are planned, the further dates are announced in time Exercises In principle, every 14 days Exercise is given on Tuesday Frontal exercise Exact dates depend upon the lecture dates Exercise sheets are provided on the web page two weeks before an exercise date April 21 st 2005 April 28 th 2005 May 12 th 2005 June 2 nd 2005 June 9 th 2005 June 16 th 2005 May 10 th 2005 June 7 th 2005 June 21 st 2005 Page 2

3 Organization Lehrstuhl für Informatik 4 Slide Copies Copies to the lecture slides as well as exercise sheets are placed on the web page to the lecture: Written Exam At the end of summer term Contact Information for questions regarding lecture/exercises Prof. Dr. Otto Spaniol, Dr. Dirk Thißen Lehrstuhl für Informatik IV, RWTH Aachen Ahornstraße 55, Aachen Phone: 0241 / / {spaniol, thissen}@informatik.rwth-aachen.de Page 3

4 Literature Lehrstuhl für Informatik 4 Books Steinmetz, R,; Nahrstedt, K.: Media Coding and Content Processing. Prentice Hall, 2002 Steinmetz, R.; Nahrstedt, K.: Multimedia Systems. Springer Verlag, 2004 Steinmetz, R.; Nahrstedt, K.: Multimedia Applications. Springer Verlag, 2004 Froitzheim: Multimedia Kommunikation. dpunkt, 1997 Magazines Multimedia Systems, ACM/Springer Multimedia Magazine, IEEE Page 4

5 What is Multimedia? Simple definition of Multimedia: Multi - Media Any kind of system that supports more than one kind of medium Is Television Multimedia? Definition: Multimedia means the integration of continuous media (e.g., audio, video) and discrete media (e.g., text, graphics, images) through which the digital information can be conveyed to the user in an appropriate way. Multi: Medium: many, much, multiple A means to distribute and represent information Page 5

6 Facets of Medium 1. Perception Medium - How do humans perceive information in a computer environment? (by seeing, by hearing,...) 2. Representation Medium - How is the information encoded in the computer? (ASCII, PCM, MPEG,...) 3. Presentation Medium - Which medium is used to output information from the computer or to bring it into the computer? Output: paper, loudspeaker, monitor,... Input: keyboard, microphone, camera, Storage Medium - Where is the information stored? 5. Transmission Medium - Which kind of medium is used to transmit the information? (copper cable, radio,...) 6. Information Exchange Medium (combination of storage and transmission media) - Which information carrier will be used for information exchange between different locations? Page 6

7 Classification of Media Each medium defines Representation values Representation space Representation values determine the information representation of different media: continuous representation values (e.g. electro-magnetic waves) discrete representation values (e.g. characters of a text in digital form) Representation space determines the technique to output the media information, usually visually (e.g., paper, slideshow) or acoustically (e.g., speakers) Spatial dimensions: Two dimensional (2D graphics) Three dimensional (holography) Temporal dimensions: Time independent (document) - discrete media (e.g. text of a book) Time dependent (movie) - continuous media (e.g. sound, video) Page 7

8 Data Streams Lehrstuhl für Informatik 4 When transmitted or played out, continuous media need a changing set of data in terms of time, i.e. data streams. How to deal with such streams? Asynchronous Transmission Suitable for communication with no time restrictions (discrete media) E.g. electronic mail Synchronous Transmission Beginning of transmission may only take place at well-defined times A clock signal runs the synchronization between a sender and a receiver Isochronous Transmission Periodic transmissions, time separation between subsequent transmissions is a multiple of a certain unit interval A maximum and a minimum end-to-end delay for each packet of a data stream (limited jitter) is required An end-to-end network connection is isochronous if it has a guaranteed bit rate and if the jitter also is guaranteed and small Page 8

9 Data Stream Characteristics Strongly periodic data streams Identical intervals T No jitter (optimally) Example: uncompressed audio T t Weakly periodic data streams Periodic intervals T Timing variations in the intervals Example: segmented transmission T 1 T 2 T 3 T 1 T 2 T 3 T T t Aperiodic data streams Arbitrary intervals Example: transmission of mouse control signals T 1 T 2 T 3 T 4 T 5 T 6 t Page 9

10 Data Stream Characteristics Strongly regular data streams Quantity remains constant during the entire lifetime of the stream Typical for uncompressed video/audio T D 1 D 1 D 1 D 1 D 1 t Weakly regular data streams T Quantity varies periodically Can result from some compression techniques E.g. videos coded with MPEG D 1 D 2 D 3 D 1 D 2 D 3 t Irregular data streams Quantity is neither constant nor periodically changing Typical for compressed audio/video Harder to transmit/process... D 1 D 2 D 3 D n t Page 10

11 Data Stream Characteristics Continuous media consist of a time-dependent sequence of individual information units: Logical Data Units (LDUs) Example: Symphony A symphony consists of independent movements, movements consists of scores Using e.g. PCM, samples are made per second. On a CD, samples are grouped into units with a duration of 1/75 second Possible LDUs with different granularity: movements, scores, groups, samples. Used in digital signal processing: sampling values as LDUs Example: Movie Consists of scenes represented by clips, clips consist of single frames, frames consist of blocks of e.g. 16x16 pixels. Pixels can consist of chrominance and luminance values Using e.g. MPEG, inter-frame coding is used, thus image sequences are the smallest sufficient LDUs Movie Clips Frames Blocks Pixels Page 11

12 Fields of the Lecture Usage Applications Learning Design User Interfaces Services Content Analysis Documents Security Synchronization Group Communication Databases Programming Systems Media Server Operating Systems Communication Optical Storage Quality of Service Networks Basics Computer Architecture Graphics & Images Compression Animation Video Audio Page 12

13 Content Lehrstuhl für Informatik 4 Chapter 2: Basics Audio Technology Images and Graphics Video and Animation Chapter 3: Multimedia Systems - Communication Aspects and Services Voice over IP, Video conferencing Group Communication, Synchronization Quality of Service and Resource Management Chapter 4: Multimedia Systems Storage Aspects Optical storage media Multimedia file systems, Multimedia databases Chapter 5: Multimedia Usage Design and User Interfaces, Abstractions for Programming Page 13