Clean Random Access Pictures for Flexible Video Seeking
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Solution Overview
Problem
Existing video codec standards limit the flexibility of random access points in video bitstreams, restricting the ability to perform operations like fast forwarding, rewinding, and seamless switching between video streams due to constraints on decodable leading pictures.
Innovation Solution
Introduce 'clean random access' (CRA) and 'broken link access' (BLA) pictures that allow non-decodable leading pictures after CRA pictures, using flags or indicators to manage these pictures, and redefine unit types and constraints to simplify mapping to container formats.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional video codec standards are used with strict constraints on random access points, then decoding reliability is maintained, but the flexibility and adaptability of video delivery and editing operations are reduced
Solution Approach 1:
The video bitstream is segmented into multiple access units, each containing a CRA picture that can serve as an independent random access point. This segmentation allows the video stream to be divided into manageable sections that can be accessed, decoded, and edited independently, thereby increasing flexibility without compromising the reliability of each segment's decoding process
Solution Approach 2:
The patent introduces dynamic constraints that allow CRA pictures to have associated leading pictures under specific conditions. The decoder dynamically determines whether to decode leading pictures based on the presence of appropriate flags and the decoding context, enabling flexible random access while maintaining decoding reliability through conditional processing
2Adaptability or versatility
If CRA pictures are allowed to have non-decodable leading pictures, then the number of access points and editing flexibility are improved, but the complexity of the decoding process increases
Solution Approach 1:
The encoder pre-flags CRA pictures and their associated leading pictures with specific syntax elements during the encoding phase. This preliminary action provides the decoder with advance information about the structure and dependencies of pictures, allowing the decoder to efficiently determine which pictures to process without increasing computational complexity during the actual decoding operation
Solution Approach 2:
The patent applies different decoding rules to different types of pictures within the access unit. CRA pictures are always decoded, while leading pictures are decoded conditionally based on their association with the CRA picture and the presence of specific flags. This local differentiation allows the system to increase the number of access points without uniformly increasing the complexity of all decoding operations
3Adaptability or versatility
If mid-bitstream CRA pictures are allowed with non-decodable leading pictures, then adaptive video delivery and production editing are enhanced, but the constraints on bitstream structure are relaxed potentially affecting standardization
Solution Approach 1:
CRA pictures serve multiple functions: they act as random access points for seeking and fast forwarding, enable production editing by providing cut points in the bitstream, and support adaptive video delivery by allowing flexible segmenting of video content. This multi-functionality is achieved through a standardized syntax structure that accommodates various operations without requiring separate mechanisms for each application
Solution Approach 2:
The patent modifies the bitstream syntax by introducing new parameters and flags (such as leading_pics_present_flag and random_access_skipped_leading_picture_flag) that control the behavior of CRA pictures and their associated leading pictures. These parameter changes allow the bitstream structure to adapt to different operational requirements while maintaining a standardized format that can be processed by compliant decoders
Data Source
AI summary
Disclosed herein are innovations for bitstreams having clean random access (CRA) pictures and/or other types of random access point (RAP) pictures. New type definitions and strategic constraints on types of RAP pictures can simplify mapping of units of elementary video stream data to a container format. Such innovations can help improve the ability for video coding systems to more flexibly perform adaptive video delivery, production editing, commercial insertion, and the like.