MPEG Reconfigurable Video Coding - Signal Processing Systems - page 293

decoding engine as well as its motion compensation engine (both are hierarchical
RV C - C AL Functional Units).
The MPEG-4 Simple Profile abstract decoder model that essentially results to
be a dataflow program (Fig. 18 , Table 2 ) , is composed of 27 atomic FUs (or actors
in dataflow programming) and 9 sub-networks (actor/network composition); atomic
actors can be instantiated several times, for instance there are 42 actor instantiations
in this dataflow program. Figure 26 shows a top-level view of the decoder. The
main functional blocks include the bitstream parser, the reconstruction block, the
2D inverse cosine transform, the frame buffer and the motion compensation module.
These functional units are themselves hierarchical compositions of actor networks.

4.6.3 MPEG-4 AVC Decoder

The MPEG-4 Advanced Video Coding (AVC), jointly developed by ISO and ITU
by which is also referred to as H.264 [ 55 ] , is a state-of-the-art video compression
standard. Compared to previous coding standards, it is able to deliver higher video
quality for a given compression ratio, and 30 % better compression ratio compared
to MPEG-4 SP for the same video quality. Because of its complexity, many
applications including Blu-ray, iPod video, HDTV broadcasts, and various computer
applications use variations of MPEG-4 AVC codec (also called profiles ). A popular
use of MPEG-4 AVC is the encoding of high definition video contents. Due to high
resolutions processing required, HD video is the application that requires the highest
performance for decoding. Common formats used for HD include 720p (1280

× 720)

and 1080p (1920 × 1080) resolutions, with frame rates between 24 and 60 frames per

second.
The decoder introduced in this section corresponds to the Constrained Baseline
Profile ( CBP ). This profile is primarily addressing low-cost applications and
corresponds to a subset of features that are in common between the Baseline , Main ,
and High Profiles .
The description of this decoder expresses the maximum of parallelism and
mimics the MPEG-4 SP. This description is composed of different hierarchical level.
Figure 19 shows a view of the highest hierarchy of the MPEG-4 AVC decoder—note
that for readability, one input represents a group of input for similar information on
each actor. The main functional block includes a parser, one luma and two chroma
decoders.
The parser analyses the syntax of the bitstream with a given formal grammar.
This grammar, written by hand, will later be given to the parser by a BSDL [ 50 ]
description. As the execution of a parser strongly depends on the context of the
bitstream, the parser incorporates a Finite State Machine so that it can sequentially
extract the information from bitstream. This information passes through an entropy
decoder and is then encapsulated in several kinds of tokens (residual coefficients,
motion vectors...). These tokens are finally sent to the selected input port of the
luma/chroma decoding actor.