Technologies de l'information — Codage des objets audiovisuels — Partie 20: Représentation de scène d'application allégée (LASeR) et format d'agrégation simple (SAF)

ISO/IEC 14496-20:2008 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,
• signaling 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.

ISO/IEC 14496-20:2008 defines the usage of SAF for LASeR content; however, LASeR can be used independently from SAF.