Wavefront Video Decoding With CTU Availability and IBC Control
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Solution Overview
Problem
Existing video coding technologies face challenges in achieving efficient parallel decoding of video bitstreams due to sequential dependencies in raster scan decoding order, limiting throughput, especially for high-resolution and high-frame-rate video sequences, and existing parallel decoding methods incur significant compression penalties.
Innovation Solution
Implement wavefront parallel processing (WPP) with modified CTU availability and intra prediction tools, such as intra block copy (IBC), by restricting state propagation and expanding reference areas to allow parallel decoding with reduced compression efficiency loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If raster scan decoding order is used, then decoding simplicity is maintained, but decoding throughput is limited due to sequential dependencies
Solution Approach 1:
The video frame is divided into multiple CTU rows that can be decoded in parallel. Each CTU row is further segmented into individual CTUs with modified availability rules, allowing multiple decoder cores to process different rows simultaneously while maintaining necessary dependencies through the wavefront delay mechanism.
Solution Approach 2:
The patent introduces dynamic wavefront delay N that adapts the parallel decoding structure. The availability of neighboring CTUs is dynamically determined based on the wavefront delay parameter, enabling flexible control over the degree of parallelization and state propagation across different decoding scenarios.
2Productivity
If parallel decoding is implemented, then decoding throughput is improved, but compression efficiency deteriorates due to sequential dependencies
Solution Approach 1:
The patent modifies the CTU availability parameter rules to enable parallel decoding. By changing the availability condition from strict sequential ordering to wavefront-based ordering with delay N, the system achieves parallel decoding capability while controlling compression efficiency loss through optimized state propagation mechanisms.
Solution Approach 2:
The wavefront delay N acts as an intermediary mechanism that mediates between parallel decoding requirements and compression efficiency. It controls the timing and extent of state information propagation between CTU rows, allowing parallel processing while minimizing compression penalties through controlled information flow.
3Productivity
If state propagation is restricted for parallel decoding, then parallel processing capability is improved, but prediction accuracy deteriorates
Solution Approach 1:
The patent applies different availability rules to different spatial locations and decoding stages. Neighboring CTUs within the same row or adjacent rows have different availability conditions based on the wavefront delay, allowing local optimization of prediction accuracy while enabling global parallel processing capability.
Solution Approach 2:
The system performs preliminary determination of CTU availability based on wavefront delay before actual decoding. This preliminary action establishes the parallel processing structure in advance, allowing prediction operations to proceed with appropriate state information available from previously decoded CTUs within the wavefront constraint.
Data Source
AI summary
A video coding method, an encoder, and a decoder are disclosed. The method is applied to a decoder and comprises retrieving a bitstream corresponding to a current frame and parsing the bitstream to obtain a current coding tree unit (CTU) of the current frame; determining an availability of at least one neighbouring CTU of the current CTU in the current frame according to a wavefront delay, wherein the wavefront delay is a delay in units of CTUs in a row direction between the current CTU at a current CTU row and the neighbouring CTU at a previous CTU row which are decoded in parallel; determining a prediction block in the at least one neighbouring CTU for a current coding unit (CU) in the current CTU; and decoding the current CU using the prediction block.