Information technology — Coding of audio-visual objects — Part 20: Lightweight Application Scene Representation (LASeR) and Simple Aggregation Format (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.
