Graphics Reference
In-Depth Information
Tabl e 2. 1
The 32 HEVC VCL NAL unit types
Trailing non-IRAP pictures
Non-TSA, non-STSA trailing
0
TRAIL_N
Sub-layer non-reference
1
TRAIL_R
Sub-layer reference
Temporal sub-layer access
2
TSA_N
Sub-layer non-reference
3
TSA_R
Sub-layer reference
Step-wise temporal sub-layer
4
STSA_N
Sub-layer non-reference
5
STSA_R
Sub-layer reference
Leading pictures
Random access decodable
6
RADL_N
Sub-layer non-reference
7
RADL_R
Sub-layer reference
Random access skipped leading
8
RASL_N
Sub-layer non-reference
9
RASL_R
Sub-layer reference
Intra random access point (IRAP) pictures
Broken link access
16
BLA_W_LP
May have leading pictures
17
BLA_W_RADL
May have RADL leading
18
BLA_N_LP
Without leading pictures
Instantaneous decoding refresh
19
IDR_W_RADL
May have leading pictures
20
IDR_N_LP
Without leading pictures
Clean random access
21
CRA
May have leading pictures
Reserved
Reserved non-IRAP
10-15
RSV
Reserved IRAP
22-23
RSV
Reserved non-IRAP
24-31
RSV
2.2.2
VCL NAL Unit Types
Tab le
2.1
shows all 32 VCL NAL unit types and their NAL unit type (NALType
in Fig.
2.2
) values in the NAL unit header. All VCL NAL units of the same access
unit must have the same value of NAL unit type and that value defines the type of
the access unit and its coded picture. For example, when all VCL NAL units of an
access unit have NAL unit type equal to 21, the access unit is called a CRA access
unit and the coded picture is called a CRA picture. There are three basic classes of
pictures in HEVC: intra random access point (IRAP) pictures, leading pictures, and
trailing pictures.
2.2.2.1
IRAP Pictures
The IRAP picture types consist of NAL unit types 16-23. This includes IDR, CRA,
and BLA picture types as well as types 22 and 23, which currently are reserved for
future use. All IRAP pictures must belong to temporal sub-layer 0 and be coded
without using the content of any other pictures as reference data (i.e., using only
“intra-picture” or “intra” coding techniques). Note that pictures that are intra coded
