Decoder-Side Motion Vector Derivation for Video Coding
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Solution Overview
Problem
Existing video coding systems face inefficiencies in motion compensation, particularly in decoder-side motion vector derivation, which increases complexity and bandwidth usage due to the need for explicit transmission of motion information and high computational complexity in bi-directional optical flow methods.
Innovation Solution
The proposed solution involves decoder-side motion vector derivation using bilateral matching and template matching techniques, where first-stage motion vectors are derived and used as initial values for second-stage searches, and bi-directional optical flow is applied only to truly bi-directional predicted blocks, reducing bandwidth and computational complexity through iterative template matching and reduced bit depth calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If motion information is explicitly transmitted from encoder to decoder, then motion compensation accuracy is maintained, but bandwidth consumption increases
Solution Approach 1:
The decoder independently derives motion vectors using template matching and bilateral matching algorithms without requiring explicit motion information transmission from the encoder. The decoder uses locally available reference picture data and neighboring block information to generate motion vectors, making the system self-sufficient and eliminating bandwidth consumption for motion information transmission.
Solution Approach 2:
The patent introduces template matching as an intermediary mechanism that bridges the gap between encoder and decoder. By matching templates from neighboring blocks with corresponding regions in reference pictures, the system derives motion vectors indirectly rather than through direct transmission, reducing bandwidth while maintaining accuracy.
2Reliability
If bi-directional optical flow is applied to all blocks, then motion compensation accuracy improves, but computational complexity increases
Solution Approach 1:
The patent applies different processing strategies to different block types. Bi-directional optical flow is applied only to blocks that require it (e.g., blocks with significant motion), while other blocks use simpler template matching or bilateral matching. This localized application of complex algorithms reduces overall computational complexity while maintaining accuracy where needed.
Solution Approach 2:
The patent segments the motion compensation process into multiple stages: first deriving initial motion vectors through template matching, then applying bi-directional optical flow only when necessary for refinement. This segmentation allows the system to avoid unnecessary computational overhead while maintaining accuracy for blocks that require it.
3Measurement precision
If first-stage motion vectors are derived using template matching, then decoder-side motion vector accuracy improves, but bandwidth usage increases due to additional data transmission
Solution Approach 1:
The decoder derives first-stage motion vectors using template matching algorithms that operate independently without requiring additional transmitted data. The decoder uses locally available information including neighboring block motion vectors and reference picture data to perform template matching and derive accurate motion vectors without increasing bandwidth usage.
Data Source
AI summary
Method and apparatus of video coding using decoder derived motion information based on bilateral matching or template matching are disclosed. According to one method, merge index for merge candidate group comprising bilateral matching merge candidate and/or template matching merge candidate are signalled using different codewords. According to another method, the first-stage MV or the first-stage MV pair is used as an only initial MV or MV pair or used as a central MV of search window for second-stage search. According to yet another method, after the reference template for a first reference list is found, the current template is modified for template search in the other reference list. According to yet another method, the sub-PU search is disabled for the template search. According to yet another method, block difference calculation is based on reduced bit depth during MV search associated with the decoder-side MV derivation process.