MPEG-7 Audio Overview Beinan Li MUMT 611 Week 2 2005. 1. 20

Content MPEG-7 overview MPEG-7 Audio What is… Why? Objectives and scope Main elements and organization. MPEG-7 Audio Low-level features High-level tools

What is MPEG-7 "Multimedia Content Description Interface“ ISO/IEC standard by MPEG (Moving Picture Experts Group) Providing meta-data for multimedia MPEG-1, -2, -4: make content available; MPEG-7: makes content accessible, retrievable, filterable, manageable (via device / computer). Multi-degrees of interpretation of information’s meaning Support as broad a range of applications as possible. A compatible (with existing tech) and extensible standard.

Why MPEG-7 “The value of information often depends on how easy it can be found, retrieved, accessed, filtered and managed. ” Past: poverty of the digital multimedia sources -> Simplicity of the access mechanisms Now: growing amount of audiovisual information -> Identifying and managing them efficiently is becoming more difficult. e.g. “record only news about sport.”

Why MPEG-7 For future multimedia services, content representation and description may have to be addressed jointly. Many services dealing with content representation will have to deal first with content description “a non-described content may be useless” Need for access only to the content description: New original services (e.g. optimizing personal time) Adaptation to networks and terminal capabilities

Application’s domains (incomplete) Broadcast media selection (e.g., radio channel, TV channel). Digital libraries (e.g., film, video, audio and radio archives). E-Commerce (e.g., personalized advertising). Education (e.g., repositories of multimedia courses, multimedia search for support material). Home Entertainment (e.g., management of personal multimedia collections, including manipulation of content, e.g. karaoke). Journalism (e.g. searching speeches of a certain politician using his name, his voice or his face). Multimedia directory services (e.g. yellow pages, G.I.S). Surveillance and remote sensing.

MPEG-7 Objectives Standardize content-based description for various types of audiovisual information Independent from media support (encoding and storage) Different granularity Low-level features: shape, size, key, tempo changes, High-level semantic info: “scene with a barking brown dog on the left and with the sound of passing cars in the background.” Meaningful in the context of the application Same material -> different types of features and combinations e.g. timbre v.s. loudness

MPEG-7 Objectives Information about the content The form: e.g. the coding format used Conditions for accessing the material: e.g. Intellectual property rights / price Classification: e.g. parental rating Links to other relevant materials The context: “e.g. Olympic Games 1996, final of 200 meter hurdles, men)” Information present in the content: Combination of low-level and high-level descriptors

Scope of the Standard processing chain:

An example of architecture Pull: (Client Queries -> Descriptions repository -> Matched Ds) Push: (Filter descriptions -> Programmed actions)

Workplan

Where are the descriptions from? Preservation of existing descriptive data (e.g. scripts) through the production/delivery Generated automatically by capture devices (e.g. time or GPS location in a camera) Extracted automatically & semi-automatically (i.e. with some human assistance) Manually produced (e.g. for legacy material such as existing film archives)

Main Elements of MPEG-7 Description Tools: ( textual / binary ) Descriptors (D): define the syntax and the semantics of each feature (metadata element) Description Schemes (DS): relationships between components Description Definition Language (DDL): Define the syntax of the MPEG-7 Description Tools Creation , extension and modification of DSs System tools: Storage and transmission, synchronization of descriptions with content, multiplexing of descriptions, etc.

Main Elements of MPEG-7 Relationship among elements introduced above.

Description Tools Creation and production processes: (director, title) Usage: (broadcast schedule) Storage features. Structural information: (spatial-temporal components) Segmentations Low level features: (sound timbres, melody description) Conceptual information: (objects and events, interactions) Navigation and access: (summaries, variations) Collections of objects. User-content interactions: (user preferences, usage history)

Organization of Description Tools

Descriptions (further) MPEG-7 approaches the description of content from several viewpoints. A set of methods and tools for the different viewpoints of the description (not a monolithic system) Interrelated and can be combined in many ways. Associated with the content itself: (searching, filtering) Location: (document V.S. stream) physically located with the material somewhere else on the globe (maybe not) Interoperability with other metadata standards: (XML)

Use of Description Tools The description tools are presented on the basis of the functionality they provide. In practice, they are combined into meaningful sets of description units. Furthermore, each application will have to select a sub-set of descriptors and DSs. Library of tools! DDL can be used to handle specific needs of the application. (like scripting in many current applications)

Major Functionalities MPEG-7 Systems MPEG-7 Description Definition Language MPEG-7 Visual MPEG-7 Audio MPEG-7 Multimedia Description Schemes (D.T.) Reference Software: the eXperimentation Model (test) MPEG-7 Conformance (syntax checking) MPEG-7 Extraction and use of descriptions (technical report)

MPEG-7 Audio Audio provides structures—building upon some basic structures from the MDS—for describing audio content. Low-level Descriptors: audio features that cut across many applications High-level Description Tools: more specific to a set of applications.

Low-level Features “MPEG-7 Audio Framework”: Two low-level descriptor types: (for sample and segment) Scalar : (e.g. power or fundamental frequency) Vector : (e.g. spectra) Hierarchical, consistent interface Any descriptor inheriting from these types can be instantiated, describing a segment with a single summary value or a series of sampled values, as the application requires. Scalable Series: (hierarchical re-sampling) Progressively down-sample the data contained in a series (Application-oriented)

Low-level Features (types) Basic Basic Spectral Signal Parameters Timbral Temporal Timbral Spectral Spectral Basis MPEG-7 Silence Descriptor

Low-level Features (graph)

Low-level Features (details) Basic: (temporally sampled scalar values for general use) AudioWaveform Descriptor waveform envelope: (for display purposes). AudioPower Descriptor temporally-smoothed instantaneous power: (quick summary of a signal) Applicable to all kinds of signals

Low-level Features (details) Basic Spectral: (single time-frequency analysis of signal) AudioSpectrumEnvelope: (Base class) the short-term power spectrum: (display, synthesize, general-purpose search) AudioSpectrumCentroid: dominated by high or low frequencies ? AudioSpectrumSpread: the power spectrum centered near the spectral centroid, or spread out over the spectrum? pure-tone and noise-like sounds AudioSpectrumFlatness: (the presence of tonal components)

Low-level Features (details) Signal Parameters: (periodic or quasi-periodic signals) AudioFundamentalFrequency: “confidence measure”, replacing “pitch-tracking” AudioHarmonicity: distinction between sounds with a harmonic / inharmonic / non-harmonic spectrum

Low-level Features (details) Timbral Temporal: (temporal characteristics of segments of sounds, musical timbre) LogAttackTime TemporalCentroid where in time the energy of a signal is focused. Useful when attack times are identical

Low-level Features (details) Timbral Spectral: (spectral features in a linear-frequency space) SpectralCentroid: power-weighted average of the frequency of the bins in the linear power spectrum. distinguishing musical instrument timbres 4 Ds for harmonic regularly-spaced components of signals: HarmonicSpectralCentroid HarmonicSpectralDeviation HarmonicSpectralSpread HarmonicSpectralVariation

Low-level Features (details) Spectral Basis: (low-dimensional projections of a spectral space to aid compactness and recognition) AudioSpectrumBasis: a series of (time-varying / statistically independent) basis functions derived from the singular value decomposition of a normalized power spectrum. AudioSpectrumProjection: low-d features of a spectrum after projection upon a reduced rank basis. independent subspaces of a spectra correlate strongly with different sound sources. Provide more salience using less space. With Sound Classification and Indexing Description Tools.

Low-level Features (details) Silence segment: (no significant sound) aid further segmentation of the audio stream, or as a hint not to process a segment

High-level audio Description Tools (Ds and DSs) Exchange some generality for descriptive richness: a smaller set of audio features (as compared to visual features) that may canonically represent a sound without domain-specific knowledge. Audio Signature (DS) Musical Instrument Timbre Melody General Sound Recognition and Indexing Spoken Content

High-level audio Description Tools (details) Audio Signature Description Scheme SpectralFlatness Ds a unique content identifier for the purpose of robust automatic identification e.g. audio fingerprinting

High-level audio Description Tools (details) Musical Instrument Timbre Description Tools HarmonicInstrumentTimbre Ds: LogAttackTime Descriptor PercussiveIinstrumentTimbre Ds: SpectralCentroid Descriptor

High-level audio Description Tools (details) Melody Description Tools: efficient, robust, and expressive melodic similarity matching. MelodyContour Description Scheme: terse, efficient melody contour / rhythm MelodySequence Description Scheme: verbose, complete, expressive melody / rhythm. Interval encoding

High-level audio Description Tools (details) General Sound Recognition and Indexing Description Tools: SoundModel Description Scheme SoundClassificationModel Description Scheme a set of SoundModel DS -> multi-way classifier SoundModelStatePath Descriptor indices to states generated by a SoundModel of a segment immediately applied to sound effects automatically index and segment sound tracks. Low -> mid -> high level analyses

High-level audio Description Tools (details) Spoken Content Description Tools: detailed description of words spoken within an audio stream. indexing into and retrieval of an audio stream indexing of multimedia objects annotated with speech. Recall of audio/video data by memorable spoken events. a character or person spoke a particular word Spoken Document Retrieval separate spoken documents Annotated Media Retrieval photograph retrieved using a spoken annotation

Development Currently under development: MPEG-7 Audio COR.1 (currently at DCOR1) MPEG-7 Amendment 1 (currently at FPDAM1) New Audio Description Tools specified (MPEG-7 version 2): Spoken Content: Audio Signal Quality: Audio Tempo: Currently Proposed tools: Low Level Descriptor for Audio Intensity Low Level Descriptor for Audio Spectrum Envelope Evolution Generic mechanism for data representation based on ‘modulation decomposition’ MPEG-7 Audio-specific binary representation of descriptors

MPEG-7 version 1 Schedule Call for Proposals October 1998 Evaluation February 1999 First version of Working Draft (WD) December 1999 Committee Draft (CD) October 2000 Final Committee Draft (FCD) February 2001 Final Draft International Standard (FDIS) July 2001 International Standard (IS) September 2001

MPEG-7 work plan: See : Annex A of MPEG-7 Overview (version 9) http://www.chiariglione.org/mpeg/standards/mpeg-7/mpeg-7.htm

Annotated Link Page / References http://www.music.mcgill.ca/~damonli/611/611_w2.htm All pictures taken from: P. Salembier and O. Avaro, “MPEG-7: Multimedia Content Description interface”, http://gps-tsc.upc.es/imatge/_Philippe/demo/MPEG21_MPEG7.pdf