Technologies de l'information - Codage des objets audiovisuels - Partie 20: Léger représentation de la scène de l'application (laser) et format simple agrégation (SAF)

This part of ISO/IEC 14496 defines a scene description format (LASeR) and an aggregation format (SAF) respectively suitable for representing and delivering rich-media services to resource-constrained devices such as mobile phones. LASeR aims at fulfilling all the requirements of rich-media services at the scene description level. LASeR supports - an optimized set of objects inherited from SVG to describe rich-media scenes,

- a small set of key compatible extensions over SVG,

- the ability to encode and transmit a LASeR stream and then reconstruct SVG content,

- dynamic updating of the scene to achieve a reactive, smooth and continuous service,

- simple yet efficient compression to improve delivery and parsing times, as well as storage size, one of the design goals being to allow both for a direct implementation of the SDL as documented, as well as for a decoder compliant with ISO/IEC 23001-1 to decode the LASeR bitstream,

- an efficient interface with audio and visual streams with frame-accurate synchronization,

- use of any font format, including the OpenType industry standard, and

- easy conversion from other popular rich-media formats in order to leverage existing content and developer communities.

Technology selection criteria for LASeR included compression efficiency, but also code and memory footprint and performance. Other aims included: scalability, adaptability to the user context, extensibility of the format, ability to define small profiles, feasibility of a J2ME implementation, error resilience and safety of implementations.

SAF aims at fulfilling all the requirements of rich-media services at the interface between media/scene description and existing transport protocols:

- simple aggregation of any type of stream,

- signalling of MPEG and non-MPEG streams,

- optimized packet headers for bandwidth-limited networks,

- easy mapping to popular streaming formats,

- cache management capability, and

- extensibility.

SAF has been designed to complement LASeR for simple, interactive services, bringing

- efficient and dynamic packaging to cope with high latency networks,

- media interleaving, and

- synchronization support with a very low overhead.

This part of ISO/IEC 14496 defines the usage of SAF for LASeR content; however, LASeR can be used independently from SAF.