Sub-Picture Motion Vector Clipping for Boundary-Safe Interpolation
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Solution Overview
Problem
Video coding systems face challenges in efficiently encoding and decoding sub-pictures due to errors caused by motion vectors pointing outside the sub-picture boundaries, leading to incomplete data retrieval and filter-related issues during independent extraction.
Innovation Solution
Implementing a clipping function and a flag to treat sub-pictures as pictures, ensuring interpolation filters operate within sub-picture boundaries, and controlling filtering at sub-picture and tile levels to prevent errors during extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If motion vectors are allowed to point outside sub-picture boundaries for better prediction accuracy, then interpolation filter precision is improved, but errors occur during independent sub-picture extraction
Solution Approach 1:
The picture is divided into independent sub-pictures with explicit boundaries. By segmenting the video content into separable units, each sub-picture can be independently decoded and extracted without requiring data from adjacent regions, thus resolving the conflict between using boundary-crossing motion vectors and maintaining extraction reliability.
Solution Approach 2:
A clipping function acts as an intermediary between the motion vector and the reference block sampling process. This mediator function ensures that sample locations are constrained to valid regions within the current picture, preventing access to invalid memory regions while preserving the ability to perform accurate interpolation filtering within bounds.
2Productivity
If sub-pictures are encoded for independent extraction, then decoding efficiency is improved, but motion compensation fails when vectors point to undecoded regions
Solution Approach 1:
The clipping function is applied in advance during the motion compensation process to prevent attempts to access undecoded or invalid reference regions. By pre-constraining the sample locations to valid picture boundaries, the system ensures that motion compensation can proceed reliably without requiring actual access to potentially undecoded adjacent sub-picture data.
3Measurement precision
If interpolation filters access data outside current sub-picture, then prediction accuracy is improved, but data availability is reduced during separate extraction
Solution Approach 1:
Different boundary handling strategies are applied to different spatial regions. Within the current picture boundaries, full interpolation filtering is performed for maximum accuracy. At the picture boundaries, clipping is applied to constrain access to valid regions. This local differentiation maintains prediction accuracy where possible while ensuring data availability during independent extraction.
Data Source
AI summary
A video coding mechanism is disclosed. The mechanism includes receiving a bitstream comprising a current picture including a sub-picture coded according to inter-prediction. A motion vector for a block of the sub-picture is determined. A clipping function is applied to sample locations in a reference block to support application of an interpolation filter when the motion vector points outside of the sub-picture and when a flag is set to indicate the sub-picture is treated as a picture. The interpolation filter is applied to results of the clipping function to obtain a predicted sample value. The block is decoded based on the predicted sample value. The block is forwarded for display as part of a decoded video sequence.