The MPEG Standard. MPEG-1 (1992) actually a video player. plays out audio/video streams same type of access as home VCR

Transcription

1 The MPEG Standard MPEG-1 (1992) actually a video player plays out audio/video streams same type of access as home VCR MPEG-2 (1995) introduced for compression and transmission of digital TV signals still limited interactivity MPEG-4 (1999) is completely different high level of interactivity MPEG-7 (2002) for the description of metadata only E.G.M. Petrakis The MPEG Standard 1

2 MPEG-4 MPEG-4 addresses the need towards Mixing of natural and synthetic audiovisual information High interactivity in the presentation of multimedia content Deployment of communication systems for realtime or broadcast delivery of coded data streams A new approach for describing, coding and presenting a scene MPEG-4 combines different coding tools for Audio/video Synthetic objects and graphics E.G.M. Petrakis The MPEG Standard 2

3 MPEG-4 Objects The audio/video components of MPEG-4 Objects are coded, transmitted separately and composed at the decoder site They can exist independently Multiple objects can be grouped together to form complex objects Video and audio can be easily manipulated Permits choosing appropriate coding tools for audio, video and graphics objects E.G.M. Petrakis The MPEG Standard 3

4 MPEG-4 Object Based Coding E.G.M. Petrakis The MPEG Standard 4

5 MPEG-4 Coding The scene is composed and rendered at the sender site video frames, audio are coded, multiplexed and transmitted tools for coding arbitrarily shaped objects At the receiver the stream is demultiplexed video and audio are decoded, composed, synchronized and presented as defined at the senders site E.G.M. Petrakis The MPEG Standard 5

6 Object Coding Objects are described mathematically (e.g. by their positions) similarly for audio and graphics objects an object need only be defined once the viewer can change their position transmit calculations to update the scene at the receiver this is a critical feature when the response has to be fast and bit-rate is limited E.G.M. Petrakis The MPEG Standard 6

7 Binary Format for Scenes (BIFS) MPEG-4 s language for describing and dynamically changing a scene Borrows concepts from VRML Both define representations of the same data VRML defines objects and actions in text BIFS code is binary (10-15 times shorter) Unlike VRML, MPEG-4 uses BIFS for realtime streaming: a scene can be built-up and played on the fly VRML and BIFS evolve consistently E.G.M. Petrakis The MPEG Standard 7

8 scene graph E.G.M. Petrakis The MPEG Standard 8

9 The Scene Graph Represents a scene as independent or compound objects e.g., father and child the audio track of his voice floor and walls (sprites: for backgrounds) the web site the synthetic image of the furniture a synthetic HDTV set playing a movie from the families DVD library E.G.M. Petrakis The MPEG Standard 9

10 Elementary Streams (ES) The scheme for preparing content for transmission, storage and decoding Objects are placed in ESs Probably two or more ESs per object A sound track or a video may have a single ES Scalable objects way have one ES for basic quality information + one or more enhancement layers for improved quality (e.g., finer detail, faster motion) ESs are split into packets and sent along with timing information for proper synchronization E.G.M. Petrakis The MPEG Standard 10

11 Object Descriptors (OD) MPEG-4s mechanism that informs the system which ES belongs to a certain object OD contain Elementary Stream Descriptors (ESD) which tell the system which decoders to use ODs are sent in their own stream which allows them to be added or deleted as the scene changes E.G.M. Petrakis The MPEG Standard 11

12 Profiles and Levels MPEG-4 provides a set of tools for coding multimedia contents an application may use only subsets of these tools Profiles: MPEG-4s definitions of these subsets for audio, visual, graphics information Levels: define the computational complexity of the profile s tool subset Certain combinations of profiles fit well together E.G.M. Petrakis The MPEG Standard 12

13 MPEG-4 Profiles E.G.M. Petrakis The MPEG Standard 13

14 MPEG-4 Visual Objects Arbitrarily shaped objects are coded apart from their background Binary shape coding: a pixel is or is not part of an object simple, crude technique, suitable for low-bit rates, suffers from aliasing Alpha shape (gray scale) coding: each pixel is assigned a value for its transparency objects can be smoothly blended into a background or with other objects E.G.M. Petrakis The MPEG Standard 14

15 Visual Objects Rectangular natural images and scenes are coded using MPEG-1, 2 Texture is coded separately by a DCT, block based coding scheme or wavelets E.g., weather reports: the weatherman s image seems to be standing in front of a map which is actually generated elsewhere E.G.M. Petrakis The MPEG Standard 15

16 Object Segmentation MPEG does not specify how objects are extracted video object segmentation is difficult e.g., record weatherman s image in front of a color background MPEG-4 specifies decoding implementation of encoding is left to the industry to decide E.G.M. Petrakis The MPEG Standard 16

17 MPEG-4 Applications MPEG-4 makes video possible even at very low bit-rates (e.g., 10 kb/s) mobile devices, internet Scalable objects for low bit-rates a base layer conveys all the information in some basic quality one of more enhancement layers can be sent to get better quality send only the most important objects E.G.M. Petrakis The MPEG Standard 17

18 Sprites For coding unchanged backgrounds The background is defined and coded only once Must be updated for each change (e.g., when the viewing angles changes) The sprite is sent only once New views are created by sending the new positions E.G.M. Petrakis The MPEG Standard 18

19 Advanced Features Map images into computer generated shapes a 2D or 3D mesh may have an image mapped onto it a few parameters to deform the mesh generate the impression of a moving picture rather than sending new images for each change, send commands and parameters to the viewer pre-defined faces are particularly interesting meshes the appearance of a face may be left to the decoder (e.g., custom facial models can be downloaded) E.G.M. Petrakis The MPEG Standard 19

20 MPEG-4 Faces Images laid over a wire-frame face Send wire-frame plus parameters Image reconstruction at receivers site Speech is generated from text in steps with motions of the mouth, eyes and lips E.G.M. Petrakis The MPEG Standard 20

21 MPEG-7 MPEG-7 (2002) focuses on description of multimedia content modalities: image, speech, video, graphics and their combinations MPEG-7 complements existing MPEG standards and is applicable even to non-mpeg formats (compressed or uncompressed) MPEG-7 is driven by trends in technology, market and user needs Applications: VideoOnDemand, NewsOnDemand, InteractiveTV, multimedia information systems etc. E.G.M. Petrakis The MPEG Standard 21

22 Scope of the Standard Provides the means for indexing, searching, filtering and managing audiovisual content broadcast media selection (e.g., personalized TV) multimedia editing (e.g., personalized news service) MPEG-7 interoperable interface defines syntax and semantics tools may be designed for specific modalities, aspects or applications E.G.M. Petrakis The MPEG Standard 22

23 Interoperable Services and Applications E.G.M. Petrakis The MPEG Standard 23

24 MPEG-7 Main Tasks Multimedia: generate customized program guides or summaries of broadcast audio-visual content Archive: generate descriptions of audiovisual content (or elements) Adaptation: filter and transform multimedia streams in low bit-rate environments (e.g., mobile users) E.G.M. Petrakis The MPEG Standard 24

25 MPEG-7 Specific Tasks Music/audio: play a few notes and return music with similar music/audio Images/graphics: draw a sketch and return images with similar graphics Movement: describe movements and return video clips with the specified temporal and spatial relations Scenario: describe actions and return scenarios where similar actions take place E.G.M. Petrakis The MPEG Standard 25

26 MPEG-7 Elements 1. Descriptors (D) : define syntax and semantics of features of audio-visual content Application independent Low level: shape, motion, color, camera motion, harmonicity, timbre for audio... Semantic level: events, concepts... E.G.M. Petrakis The MPEG Standard 26

27 MPEG-7 Elements (cont.d) 2. Description Schemes (DS): specify the structure and semantics of the relationships among the constituent Ds or DSs e.g., Video DS specify syntax and semantics for segment decomposition, attributes, their relationships DS related to creation, production, and access of content (e.g., property rights, parental rating, etc.) E.G.M. Petrakis The MPEG Standard 27

28 MPEG-7 Elements (cont.d) 3. Description Definition Language (DDL): allows flexible definition of Ds and DSs based on XML schema Ds and DSs are application independent DLLs to define specialized tools E.G.M. Petrakis The MPEG Standard 28

29 MPEG-7 Descriptions MPEG-7 allows descriptions at different levels of abstractions low level features extracted automatically semantic features with human interaction or textual annotation MPEG-7 does not specify how features are extracted or used (e.g., filtering, retrieval) their representation must conform to the MPEG-7 standard E.G.M. Petrakis The MPEG Standard 29

30 MPEG-7 Parts Systems: specifies functionality at system level Preparation of descriptions for efficient transport and storage synchronization of content and descriptors development of decoders Description Definition Language (DDL): language for specifying new Ds and DSs extension of XML schema E.G.M. Petrakis The MPEG Standard 30

31 MPEG-7 Visual Specifies a set of standardized visual Ds and DSs Color descriptors: color space, quantization Texture descriptors: homogeneous texture, texture browsing, edge histogram... Shape descriptors: for regions or contours Motion descriptors: camera motion, trajectories, motion activity... Face recognition E.G.M. Petrakis The MPEG Standard 31

32 MPEG-7 Audio Specifies standardized audio descriptors and descriptor schemes for pure music, pure speech, sound effects, soundtracks silence descriptor spoken content descriptors sound effects descriptors melody contour descriptors E.G.M. Petrakis The MPEG Standard 32

33 Multimedia Description Schemes Specify a framework that allows generic description of all kinds of multimedia data basic elements: data types, structures, Ds content management: content from several viewpoints (creation, usage etc.) organization of content by collections, classification navigation and access user interaction E.G.M. Petrakis The MPEG Standard 33

34 Multimedia Description Schemes E.G.M. Petrakis The MPEG Standard 34

35 MPEG-7 Reference Software Reference implementation of the relevant parts of the MPEG-7 standard The focus is on creating bit-streams of descriptors and description schemes (DDL parser, DDL validation, multimedia description schemes) Some software for extracting descriptors is also included (visual, audio descriptors) E.G.M. Petrakis The MPEG Standard 35

36 References 1. MPEG-4 Multimedia for our Time R. Koenen, IEEE Spectrum, Feb. 1999, pp Applying and Implementing the MPEG-4 Multimedia Standard, J. Kneip et.al. IEEE Micro, Nov-Dec 1999, pp Overview of the MPEG-7 Standard, S.-Fu Chang, T. Sikora and A. Puri, IEEE Transactions on Circuits and Systems for Video Technology, special issue on MPEG-7, June Everything You Wanted to Know about MPEG-7 F. Nack and A.T. Lindsay, Part I, II, IEEE Multimedia, Aug-Dec1999 E.G.M. Petrakis The MPEG Standard 36