Mixed NAL Unit Type Support in Coded Pictures
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Solution Overview
Problem
The current Versatile Video Coding (VVC) specification faces issues with ambiguous picture types, conflicting temporal identifier constraints, and the inability to support the coexistence of certain NAL unit types in a coded picture.
Innovation Solution
A method is introduced to determine the picture type of a coded picture based on the mixed VCL NAL unit types, using indicators such as flags in the picture header or slice header, to resolve conflicts and allow for the coexistence of specific NAL unit types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mixed NAL unit types are supported in a coded picture, then the versatility and adaptability of video coding is improved, but the complexity of picture type determination and temporal identifier constraint resolution increases
Solution Approach 1:
The picture is divided into slices, each with its own NAL unit type (IRAP or non-IRAP), allowing independent processing and type determination for each slice while maintaining overall picture structure. This segmentation enables mixed NAL unit types without overwhelming complexity in the entire picture.
Solution Approach 2:
The flag `mixed_nalu_types_in_pic_flag` is set in advance during encoding to indicate whether a picture contains mixed NAL unit types. This preliminary indication allows the decoder to prepare appropriate processing logic before encountering the actual mixed NAL units, simplifying real-time decision-making.
2Adaptability or versatility
If multiple NAL unit types coexist in a picture, then the flexibility of random access periods is improved, but conflicts in temporal identifier constraints arise
Solution Approach 1:
Different slices within the same picture are assigned different NAL unit types (IRAP or non-IRAP) according to their specific requirements. Each slice maintains its own temporal identifier constraints locally, allowing IRAP slices to support random access while non-IRAP slices maintain normal temporal dependencies, thus resolving conflicts at the slice level rather than picture level.
Solution Approach 2:
The flag `mixed_naluTypesInPicFlag` acts as an intermediary indicator that signals the presence of multiple NAL unit types in a picture. This mediator allows the decoder to understand and properly interpret the mixed structure, enabling reliable constraint resolution by knowing in advance which slices require special temporal handling.
3Measurement precision
If the syntax element mixed_naluTypesInPicFlag is used to indicate mixed NAL unit types, then the clarity of picture type determination is improved, but the complexity of syntax structure increases
Solution Approach 1:
The flag `mixed_naluTypesInPicFlag` serves multiple functions: it indicates the presence of mixed NAL unit types, triggers special picture type determination logic, and enables appropriate constraint application for temporal identifiers. By consolidating these multiple functions into a single flag, the syntax structure remains relatively simple while achieving precise picture type determination.
Data Source
AI summary
Methods and systems are provided for decoding at least one video stream. A method includes receiving a first network abstraction layer (NAL) unit of a first slice of a coded picture and a second VCL NAL unit of a second slice of the coded picture, the first VCL NAL unit having a first VCL NAL unit type and the second VCL NAL unit having a second VCL NAL unit type that is different from the first VCL NAL unit type, and decoding the coded picture, the decoding including determining a picture type of the coded picture based on the first VCL NAL unit type of the first VCL NAL unit and the second VCL NAL unit type of the second VCL NAL unit, or based on an indicator, received by the at least one processor, indicating that the coded picture includes mixed VCL NAL unit types.