TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI
TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI
TITRE Adaptive Packet Video Streaming Over IP Networks - LaBRI
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A.3 Object Description Framework<br />
The purpose of the MPEG-4 object descriptor framework is to identify, describe and associate<br />
elementary streams with the various components of an audiovisual scene [22]. A “bootstrap”<br />
stream describes the streaming resources used in a virtual world. A media object is associated to its<br />
elementary stream resources via an object descriptor. The Figure A-4 shows the principle of MPEG-<br />
4 Object Descriptor.<br />
initial<br />
ObjectDescriptor<br />
ES_Descriptor<br />
:<br />
ES_Descriptor<br />
ES_ID<br />
BIFS Update (Replace Scene)<br />
Scene Description<br />
Scene Description Stream<br />
e.g. Audio<br />
Source<br />
e.g. <strong>Video</strong><br />
Object<br />
2D<br />
ES_ID<br />
ObjectDescriptorID<br />
ObjectDescriptorUpdate<br />
ObjectDescriptor<br />
Object Descriptor Stream<br />
Object<br />
Descriptor<br />
ES_D<br />
ES_D<br />
Object<br />
Descriptor<br />
... ...<br />
ES_D<br />
...<br />
...<br />
ES_Descriptor<br />
:<br />
ES_Descriptor<br />
ES_ID<br />
ES_ID<br />
Visual Stream (e.g. base layer)<br />
Visual Stream (e.g. temporal enhancement)<br />
Audio Stream<br />
Figure A-4: MPEG-4 object descriptor structure<br />
A.3.1 Object Descriptor<br />
An object descriptor is a collection of one or more Elementary Stream descriptors that<br />
provide configuration and other information for the streams that relate to a single object (media<br />
object or scene description. Each object descriptor is assigned an identifying number (Object<br />
Descriptor ID), which is unique within the current session. This identifier is used to associate media<br />
objects in the Scene Description with a particular object descriptor, and thus the elementary<br />
streams related to that particular object.<br />
Elementary Stream descriptors include information about the source of the stream data, in<br />
form of a unique numeric identifier (the Elementary Stream ID) or a URL pointing to a remote<br />
source for the stream. ES IDs are resolved to particular delivery channels at the transport layer. ES<br />
Descriptors also include information about the encoding format, configuration information for the<br />
decoding process and the Sync Layer packetization, as well as QoS (quality of service) requirements<br />
for the transmission of the stream and intellectual property identification. Dependencies between<br />
streams can also be signalled, for example to indicate dependence of an enhancement stream to its<br />
base stream in scalable AVO representations, or the availability of the same speech content in<br />
various languages.<br />
A.3.2 Initial Object Descriptor<br />
Initial object descriptors (IODs) serve to access MPEG-4 content. The IOD is an object<br />
descriptor that does not only describe a set of elementary streams, but it also conveys the set of<br />
profile and level information that is needed by a receiver to assess the processing resources needed<br />
for that content.<br />
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