Video Decoder Motion Prediction With Substitute Syntax Values
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Solution Overview
Problem
In video coding, certain syntax elements for motion information, such as bi-prediction with CU-level weights (BCW), are not assigned values for uni-predicted blocks, leading to inconsistencies and increased complexity in video coder performance.
Innovation Solution
Implementing substitute values for missing syntax elements, such as using a default value for bi-prediction syntax elements when neighboring blocks are uni-predicted, ensuring harmonized motion information prediction across various scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If bi-prediction syntax elements are not assigned values for uni-predicted blocks, then memory bandwidth usage is reduced, but video coder complexity increases due to inconsistent motion information prediction
Solution Approach 1:
The patent applies parameter changes by introducing a new syntax element 'interDir' that explicitly indicates the inter prediction direction (uni or bi). This allows the decoder to determine whether to expect bi-prediction syntax elements without requiring them to be present in all cases, thereby reducing memory bandwidth usage while maintaining consistent motion information prediction through the explicit direction indicator.
Solution Approach 2:
The patent segments the prediction process by separating uni-prediction and bi-prediction into distinct categories indicated by the 'interDir' syntax element. This segmentation allows the decoder to selectively process only the relevant syntax elements for each prediction type, reducing unnecessary memory operations and simplifying the coding logic by clearly defining when each prediction mode applies.
2Stability of the object's composition
If substitute values are used for missing syntax elements, then motion information prediction consistency is improved, but coding overhead increases
Solution Approach 1:
The patent introduces a new parameter 'interDir' that explicitly indicates the prediction direction type. This parameter change eliminates the need for substitute values by providing clear information about whether bi-prediction syntax elements should be present, thereby maintaining motion information prediction consistency without adding unnecessary coding overhead from default value assignments.
Solution Approach 2:
The patent applies preliminary action by indicating the prediction direction type before processing motion information syntax elements. The 'interDir' syntax element is decoded first, allowing the decoder to prepare appropriately for the specific prediction mode and avoid unnecessary processing of absent syntax elements, thus maintaining consistency without increasing overhead.
3Loss of information
If bi-prediction syntax elements are always present in the bitstream, then motion information availability is improved, but bitstream size increases
Solution Approach 1:
The patent changes the parameter structure by introducing 'interDir' to explicitly indicate prediction direction type. This allows the bitstream to selectively include bi-prediction syntax elements only when needed (for bi-predicted blocks), ensuring motion information availability for relevant blocks while avoiding unnecessary data transmission for uni-predicted blocks, thus reducing overall bitstream size.
Solution Approach 2:
The patent applies partial action by including bi-prediction syntax elements in the bitstream only partially - specifically, only for blocks that actually use bi-prediction mode as indicated by the 'interDir' syntax element. This avoids the excessive action of always including these elements for every block, thereby maintaining motion information availability where needed while reducing bitstream size by eliminating redundant data.
Data Source
AI summary
An example device for decoding video data includes a memory configured to store video data; and a processing system including one or more processors implemented in circuitry, the processing system being configured to: determine that a previously coded block of video data was coded using uni-prediction mode for which a bi-prediction syntax element is not assigned a value; determine that a current block of the video data is to be coded using a bi-prediction mode and that motion information of the current block is to be predicted from the previously coded block, including from the bi-prediction syntax element of the previously coded block; and in response to the bi-prediction syntax element of the previously coded block not having an assigned value, decode the current block using a substitute value for the bi-prediction syntax element.