The role of these concepts : for communication (compatibility) between different implementations that require similar functions. Personally understand that the encoded video has different grades, there are different levels under a certain grade, and there are different levels in a certain level, and these same encoded videos can be compatible when they are decoded. , That is, a decoder that supports a certain level, level, and level can decode other low-level, low-level, and low-level encoded videos.
The meaning of profile in HEVC
Concept : profile is a description of the compression characteristics of the video, specifically referring to the coding algorithms and coding tools used in the bitstream
Three profiles are supported in HEVC, namely main profile, main 10-bit profile, and main still profile. The relationship between them is shown in the figure below. Levels can be compatible with inner levels
Features of the main profile (mian profile)
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Bit depth is limited to 8bit
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Sampling format is limited to 4: 2: 0
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The size of CTB is from 16 * 16 to 64 * 64
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The buffer capacity of the decoded image is limited to 6 images
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Allows selection of wavefront and slice division, but not simultaneous selection
Features of 10-bit main profile
- The main features are similar to the main profile, but the difference is that it can support 10-bit depth
Features of main still profile
- The main features are similar to the main profile, but the difference is that it does not support inter-frame predictive encoding, and the entire code stream of the video can only be encoded in one frame.
Description:
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In terms of decoder compatibility, a decoder supporting a certain profile must support the profile and all features below it (backward compatibility);
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In the H265 encoder, an encoder is not required to support all the features of a profile, but the encoded bitstream must conform to the HEVC standard, such as following the constraints of a compatible decoder to be supported by the profile Decoded by the decoder.
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Minimizing the number of profiles can achieve the effect of enhancing the versatility of the device,
The meaning of Level in HEVC
Concept : Level indicates the constraints of some key parameters that have a greater impact on the decoding end load and memory occupation. These parameters mainly include: sampling frequency, resolution, maximum bit rate, minimum compression rate, decoding The capacity of the graphics buffer (DPB) and the capacity of the coded image buffer (CPB); the horizontal also constrains the maximum number of tiles in the vertical and horizontal directions in each frame, and the maximum number of tiles per second.
Explanation : In HEVC, there are 13 levels in total. A level is simply a set of coding parameters.
The meaning of level (tire) in HEVC:
Concept : The level specifies the bit rate of each level
Description :
For the same level, according to the difference between the maximum code rate and the buffer capacity, HEVC has set two file levels, namely high level and main level
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The main level can be applied to most scenarios, and the required bit rate is lower
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High level can be used for special requirements or demanding scenes
Summary: profile specifies what encoding tools and encoding algorithms are used for video encoding, Level specifies the encoding parameters of a certain level, and tier specifies the maximum bit rate of a certain level of a profile
