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1.HEVC's Profiles, Levels, Tier (Layer)
1.1 HEVC PROFILES (grade)
1.2 HEVC Levels (Level) and Tiers (Layers)
2.Hevc hierarchical structure
2.1 Structure overview
2.2 VCL
2.2 NAL
2.2.1 Nal Unit header included:
2.2.2 VCL-NALU and NON VCL-NALU specific types are as follows:
2.2.3 nalu payload
1.HEVC's Profiles, Levels, Tier (Layer)
1.1 HEVC PROFILES (grade)
Profile specifies which codecs can use which coding tools or algorithms, a total of three grades: (1) "Main" Profile: The bit deep per pixel 8bit is the most common grade. (2) "Main STILL PICTURE" Profile: Supports a single static image, encoding according to the MAIN grade, BitStream Contains Only A Single (intra) Picture Includes All (intra) Coding Features of Main Profile (3) "Main 10" Profile : In addition to the depth of 8bit, it is also extended to support the 10bit derption. The decoder that supports main 10 must decode the MAIN grade stream.
1.2 HEVC Levels (Level) and Tiers (Layers)
Level is a combination of a series of coded constraints that affect the load and memory of decoding ends, such as maximum sampling rate, maximum image size, minimum compression ratio, maximum bit rate, DPB capacity, and CPB (decoded buffer) size. Wait.
Tier (layers) is distinguishing between the highest bit rate required for different applications, there are two types of main and high.
Standard specification HEVC has 13 Level (levels) and 2 tier (layers):
2.Hevc hierarchical structure
2.1 Structure overview
Similar to H.264 / AVC, H.265 / HEVC adopts video codewer, VCL and network adaptation layer (NAL), and the VCL layer contains video data content, and NAL is mainly responsible. Divide and encapsulate data after video compression, ensuring that data can be transmitted in different network environments. With NAL, video compression data will be divided into NAL units (NAL Unit, NALU) having different characteristics according to their content characteristics, and identify the content characteristics of NALU. Therefore, the transmission network can optimize the performance of the video transmission according to the NALU identifier, without having to analyze the content characteristics of the video. NALU can be transferred directly as a carrier, and due to the Maximum Transmission Unit, MTUs supported by different networks, there is a network packet containing one or more NALUs, or multiple network packets containing a NALU.
CAPTION
The NetWork Abstract Layer in the above figure belongs to the contents of other protocol definitions. VCL can be considered to be a nude code stream after video encoding, and NAL is a code stream for packed VCL bare code streams.
BitStream is a Nal Units composition
2.2 VCL
The VCL uses a hybrid encoding technique that combines the compression technique of static compression in the picture, the dynamic compression, 2D transformation, and the entropy compression of the code stream. The encoding frame is shown below:
Typical HEVC encoder structure
Compared with H.254 / AVC, H.265 / HEVC uses many new coding methods as shown in the following table:
HEVC / H.265 AVC / H.264 Year Other Name Resolutions 2013 MPEG-H UP To 8K 2003 MPEG-4 Part 10 Up to 4k Profiles 3 Profiles; 13 Levels; 2 Tiers 21 Profiles; 17 Levels Block Size Tree Structure 8x8, 16X16, 32X32, 64x64 Square, Sym./asym. Rect. Macroblock 16x16 (4x4) Square, Sym. Rect. Transforms Integer-DCT (4x4, 8x8, 16x16, 32x32) Integer-DST (4x4 intra) Integer-DCT (4x4 , 8X8) Hadamard (2x3, 4x4) intra-prediction Up to 33 Angular Modes (+ DC + Planar Mode) Up to 9 modes motion predomation motion-copy mode mv precision Advanced MV PREDICTION (Spatial + Temp. Co-located) MERGE, Skip 1/4 pixel 7/8 tap Spatial mediam + temp. co-located Direct, Skip 1/2 pixel 6-tap + 1/4 pixel bilinear In-loop filtering deblocking, SAO deblocking Quantization Entropy Coding URQ CABAC URQ CAVLC, CABAC
2.2 NAL
The HEVC code stream is composed of a series of NAL UNIT (NALU), each NAL contains data of integer bytes, and the first two bytes are NAL Unit header (1 byte in h.264), the remaining load data (original word) Sequence load RBSP). Different NAL units are divided into VCL NAL and NON VCL NAL units, and the former carries encoded image data, which contains multi-frame shared control parameter information.
HEVC NAL structure
2.2.1 Nal Unit header included:
The first bit'f 'is the Forbidden-Zero bit, fixed to 06-bits naltype to determine the type of NAL, where VCL NAL and NON-VCL NAL have 32 class Layerid indicate the layer of Access Unit in NAL, which is for HEVC's continued extension setting TID (Temporal Identifier) determines the hierarchical level on the time domain of the NAL in the UNIT, as shown below: For A, B The NAL, TID field content in the same picture is the same. Role: TID small NAL cannot rely on TID large NAL, and can also be used to control video selection partial frames.
2.2.2 VCL-NALU and NON VCL-NALU specific types are as follows:
NAL type
2.2.3 nalu payload
NALU load length is integer byte, carrying the original byte sequence load after video compression (RBSP). RBSP is a package that adds a tail (String of Data Bits) after video encoding (add end bit 1 to make up the whole byte) package. The RBSP can contain an SS compressed data, VPS, SPS, PPS, supplemental enhancement information, etc., or for the delimitation, the sequence end, the bit stream end, filling data, and the like. In the byte stream environment, if the corresponding SLICE corresponding to the NALU is the beginning of a frame, the start code is 0x00000001. If the corresponding SLICE is not a frame, it is 0x000001. To avoid conflicts with the starting code and end code in the NALU load and NALU, the RBSP byte stream needs to be avoided to avoid collision processing, and the processed RBSP can be directly used as the load information of NALU. At the same time, it is noted that these treatments are restored inversely when decoding.
Below is a diagram of Nalu Sequence of H.264 / AVC:
H.264 NALU SEQUENCE
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