MPEG Reconfigurable Video Coding - Signal Processing Systems - page 283

The untimedness and asynchrony of stream-based programming offers a solution
to this problem. The portability of stream-based programs is underlined by the fact
that programs of considerable complexity and size can be compiled to competitive
hardware [ 32 ] aswellassoftware[ 52 ] , which suggests that stream-based program-
ming [ 33 ] might even be a solution to the old problem of flexibly co-synthesizing
different mixes of hardware/software implementations from a single source.

Encapsulation. The success of a stream programming model will in part depend
on its ability to configure dynamically and to virtualize, i.e. to map to collections
of computing resources too small for the entire program at once. Moving parts
of a program on and off a resource requires encapsulation, i.e. a clear distinction
between those pieces that belong to the parts to be moved and those that do not.
The transactional execution of actors generates points of quiescence , the moments
between transactions, when the actor is in a defined and known state that can be
safely transferred across computing resources.

4 Description of the Standard or Normative Components

of the Framework

The fundamental element of the RVC framework, in the normative part, is the
Decoder Description (Fig. 2 ) that includes two types of data:
The Bitstream Syntax Description (BSD), which describes the structure of the
bitstream. The BSD is written in RVC-BSDL. It is used to generate the appropriate
parser to decode the corresponding input encoded data [ 25 , 50 ] .
The FU Network Description (FND), which describes the connections between
the coding tools (i.e. FUs). It also contains the values of the parameters used for
the instantiation of the different FUs composing the decoder [ 14 , 32 , 52 ] . The FND
is written in the so called FU Network Language (FNL). The syntax parser (built
from the BSD), together with the network of FUs (built from the FND), form a
C AL model called the Abstract Decoder Model (ADM), which is the normative
behavioral model of the decoder.

4.1 The Toolbox Library

An interesting feature of the RVC standard that distinguishes it from traditional
decoders-rigidly-specified video coding standards is that, a description of the
decoder can be associated to the encoded data in various ways according to each
application scenario. Figure 4 illustrates this conceptual view of RVC [ 41 , 43 ] .
All the three types of decoders are within the RVC framework and constructed
using the MPEG-B standardized languages. Hence, they all conform to the MPEG-