Graphics Reference
In-Depth Information
For future extensibility, the PPS contains syntax elements indicating extensions
to the slice segment header. A syntax element indicates a number of extra slice
header bits, in the range of 0-7, to be included at the beginning of the slice header.
In addition, a slice segment header extension flag in the PPS indicates the presence
of additional bits at the end of the slice segment header.
2.3.4
The Slice Segment Header
The slice segment header contains an index to a reference PPS. The slice segment
header contains data identifying the slice segment, including a first slice segment
in picture flag and a slice segment address. When dependent slices are used, a slice
may be split into multiple slice segments. Some parameters are included only in the
first slice segment of a slice, including the slice type (I, P, or B), picture output flag,
and long term and short term RPS info (described in more detail in Sect.
2.4.2
).
The presence of some coding tool parameters are present in the slice segment
header if the tools were enabled in the SPS or PPS, including enabling SAO
separately for luma and chroma, enabling deblocking filter operation across slices,
and an initial slice quantization parameter (QP) value. Deblocking filter parameters
may either be present in the slice segment header or the PPS. If tiles or wavefronts
are used, entry points are provided in the slice segment header.
Optional extra slice segment header bits may be included at the beginning of the
slice segment header, when indicated in the PPS. Their use is intended for future
extensibility, to allow association of parameters with a backwards compatible base
layer in a manner that is easily accessible by systems entities.
2.3.5
System Layer Integration Aspects
Virtually all applications of video codecs involve some type of systems interface,
for storage and/or transport, and to provide timing information and alignment of the
video with other media types, such as audio. Because the HEVC high level syntax
design has much commonality with AVC, the systems and transport standards used
for carriage of AVC can be updated to carry HEVC [
8
]. Both HEVC and AVC
were designed with network friendliness being a key design goal. The key elements
of the HEVC design relevant to the systems interfaces are the NAL unit design,
parameter sets, and SEI messages. The main systems standards of interest are Real-
time Transport Protocol (RTP) [
11
], MPEG-2 systems [
3
,
4
], and ISO Base Media
File Format (ISOBMFF) [
5
]. Many other systems and application specifications
build upon these three standards. For example, several file format specifications and
Dynamic Adaptive Streaming over HTTP (DASH) [
6
] are based upon ISOBMFF,
most broadcast standards use MPEG-2 systems, and most IP videoconferencing
applications use RTP.
