Graphics Reference
In-Depth Information
sequence, which can be useful for systems interfaces. Other parameters describe
usage of coding tools, or provide coding tool parameters, which can improve bit rate
efficiency. Additionally, the SPS can optionally contain Video Usability Information
(VUI) data which provides information that does not directly impact the decoding
process, as described in Sect.
2.5
.
Key parameters describing the characteristics of the coded sequence are included
in the SPS. The profile, tier, and level indications specify conformance points,
similar to the profile and level definitions in AVC. A profile defines a set of coding
tools, a level imposes capability restrictions on maximum sample rate, picture
size, and capabilities of the DPB, etc. HEVC introduces a tier indication, which
in combination with level, imposes a maximum bit rate restriction. The coded
picture height and width in luma samples are included in the SPS, as well as the
conformance window cropping parameters to indicate the output region of the coded
picture. Luma and chroma bit depth are also indicated, and their allowable values
are constrained by profiles. The SPS also contains some duplicated information from
the VPS related to temporal scalability, as described in Sect.
2.3.1
.
The SPS also contains parameters to enable or disable coding tools, or to set
restrictions on coding tools. In some cases, a coding tool enable flag in the SPS
allows a coded slice to avoid containing syntax elements related to the unused
coding tool. Examples of tools with enable flags are asymmetric motion partitioning
(AMP) as described in Chap.
3
, Sample Adaptive Offset (SAO) as described in
Chap. 7, and PCM coding as described in Chap. 6. Restrictions on the coding tree
block and transform unit sizes are also signaled.
The SPS also can optionally include coding tool parameters, which may also be
sent at lower layers if per picture variation is used. These include scaling list data,
which provides quantization matrices as described in Chap. 6, and reference picture
set (RPS) data as described in Sect.
2.4.2
.
2.3.3
The Picture Parameter Set (PPS)
The PPS contains parameters that may change for different pictures within the
same coded video sequence. However, multiple pictures may refer to the same
PPS, even those with different slice coding types (I, P, and B). Including these
parameters within parameter sets rather than within the slice header can improve
bit rate efficiency and provide error resiliency when the PPS is transmitted more
reliably.
The PPS contains a PPS identifier, as well as an index to a reference SPS. The
remaining parameters describe coding tools used in the slices which refer to the
PPS. Coding tools are enabled or disabled, including dependent slices, sign data
hiding, constrained intra prediction, weighted prediction, trans/quant bypass, tiles,
and reference list modification. Coding tool parameters signaled in the PPS include
the number of reference indices, initial quantization parameter (QP), and chroma
QP offsets. Coding tool parameters may also be signaled in a PPS, e.g. deblocking
filter controls, tile configurations, and scaling list data.
