Temporal Motion Vector Prediction Reference Index Adjustment
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Solution Overview
Problem
In video coding, particularly in High-Efficiency Video Coding (HEVC) and its extensions, the use of temporal motion vector prediction (TMVP) is hindered by inaccuracies when reference pictures from different types (disparity and temporal) are used, leading to decreased coding efficiency and increased bitstream size.
Innovation Solution
The solution involves setting the reference index of a temporal merging candidate to a non-default value when the initial and indicated reference pictures belong to different reference picture types, allowing the video coder to select a more appropriate reference picture from the reference picture list, thereby improving the rate/distortion value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the reference index of a temporal merging candidate is set to a default value (0) regardless of reference picture type compatibility, then the coding process is simpler and faster, but the motion prediction accuracy deteriorates when initial and indicated reference pictures belong to different reference picture types
Solution Approach 1:
The patent changes the reference index parameter from a fixed default value (0) to a dynamically selected value based on reference picture type compatibility. When the initial reference picture and the picture indicated by the temporal motion vector predictor belong to different reference picture types, the reference index is changed to point to a different position in the reference picture list that ensures type compatibility, thereby maintaining motion prediction accuracy without excessive complexity.
2Productivity
If the reference index is adjusted to match reference picture types, then the coding efficiency improves, but the bitstream size increases due to additional signaling requirements
Solution Approach 1:
The patent employs a self-service mechanism where the decoder autonomously determines the appropriate reference index based on the temporal merging candidate information and reference picture list configuration. The decoder checks whether the initial reference picture and the picture indicated by the temporal motion vector predictor belong to different reference picture types, and if so, automatically selects a suitable reference index without requiring explicit signaling from the encoder, thus avoiding additional bitstream overhead.
3Loss of information
If temporal motion vector prediction is disabled when reference pictures belong to different types, then the coding complexity is reduced, but the loss of information increases due to unavailable motion candidates
Solution Approach 1:
The patent introduces an intermediary mechanism that bridges the gap between temporal motion vector prediction and reference picture type compatibility. Instead of directly disabling TMVP when types differ, the system uses the reference picture list as an intermediary structure that can accommodate both types. By selecting an appropriate reference index that points to a compatible reference picture within the list, the system maintains motion information availability while managing the complexity of type checking through structured reference picture organization.
Data Source
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AI summary
A first reference index value indicates a position, within a reference picture list associated with a current prediction unit (PU) of a current picture, of a first reference picture. A reference index of a co-located PU of a co-located picture indicates a position, within a reference picture list associated with the co-located PU of the co-located picture, of a second reference picture. When the first reference picture and the second reference picture belong to different reference picture types, a video coder sets a reference index of a temporal merging candidate to a second reference index value. The second reference index value is different than the first reference index value.