Graphics Reference
In-Depth Information
2.1
Introduction
The “high-level syntax” part of HEVC [
7
,
9
] includes the structure of the bitstream
as well as signaling of high-level information that applies to one or more entire slices
or pictures of a bitstream. For example, the high-level syntax indicates the spatial
resolution of the video, which coding tools are used, and describes random access
functionalities of the bitstream. In addition to the signaling of syntax elements, the
high-level tool decoding processes associated with the syntax elements are also
considered to be included in the high level syntax part of the standard. Example
high-level syntax decoding processes include reference picture management and
the output of decoded pictures.
Figure
2.1
shows an HEVC encoder and decoder. Input pictures are fed to an
encoder that encodes the pictures into a bitstream. An HEVC bitstream consists of a
sequence of data units called network abstraction layer (NAL) units, each of which
contains an integer number of bytes. The first two bytes of a NAL unit constitutes
the NAL unit header, while the rest of the NAL unit contains the payload data.
Some NAL units carry parameter sets containing control information that apply to
one or more entire pictures, while other NAL units carry coded samples within an
individual picture.
The NAL units are decoded by the decoder to produce the decoded pictures
that are output from the decoder. Both the encoder and decoder store pictures in
a decoded picture buffer (DPB). This buffer is mainly used for storing pictures so
that previously coded pictures can be used to generate prediction signals to use when
coding other pictures. These stored pictures are called reference pictures.
Each picture in HEVC is partitioned into one or multiple slices. Each slice is
independent of other slices in the sense that the information carried in the slice is
coded without any dependency on data from other slices within the same picture. A
slice consists of one or multiple slice segments, where the first slice segment of a
slice is called independent slice segment and is independent of other slice segments.
The subsequent slice segments, if any, are called dependent slice segments since
they depend on previous slice segments.
Decoder
Decoding
engine
Encoder
Encoding
engine
NAL units
Bitstream
DPB
DPB
Input
pictures
Decoded
pictures
Fig. 2.1
Overview of HEVC encoding and decoding
