HEVC Decoder DQP Signaling for Parallel Processing
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Solution Overview
Problem
The standard Delta Quantization Parameter (DQP) syntax in HEVC introduces delays in decoding due to its placement at the end of a Largest Coding Unit (LCU), and unnecessarily sends DQP bits when they are not needed, such as in SKIP modes or when all coefficients are zero, wasting resources.
Innovation Solution
Modifying the bitstream syntax to place the DQP immediately after the mode information of the first coding unit, or after the first non-skipped coding unit, or after the first non-zero coded block flag, allowing for parallel processing and pipelining in decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DQP is placed at the end of LCU in standard syntax, then rate control and region-of-interest coding are improved, but decoding delay increases and pipeline length is extended
Solution Approach 1:
The DQP value is signaled in advance at the beginning of the LCU syntax structure, before the actual decoding of coding units occurs. This preliminary signaling allows the decoder to have the quantization parameter ready before processing starts, eliminating the waiting delay that would occur if DQP were signaled at the end of LCU.
Solution Approach 2:
The DQP signaling is separated from the end-of-LCU position and placed at the beginning, creating distinct segments for parameter signaling and decoding operations. This segmentation allows independent processing of DQP extraction and subsequent decoding stages, enabling pipeline parallelization.
2Reliability
If DQP is signaled at the end of LCU, then region-of-interest coding is improved, but productivity decreases due to increased pipeline length
Solution Approach 1:
By signaling DQP at the beginning of LCU rather than at the end, the decoder can extract quantization parameters before the main decoding pipeline processes the coding units. This preliminary action enables parallel processing where DQP extraction and decoding operations occur simultaneously, increasing throughput.
Solution Approach 2:
The modified syntax structure acts as an intermediary that separates parameter signaling from decoding operations, allowing the DQP value to be made available to multiple decoding pipelines simultaneously without creating sequential dependencies.
3Reliability
If DQP is always signaled in standard syntax, then completeness is ensured, but bit waste occurs when DQP is unnecessary
Solution Approach 1:
Instead of always signaling DQP unconditionally, the patent applies partial signaling by including DQP only when necessary (when transform coefficients are present). This selective approach transmits fewer bits than the excessive action of always signaling, while still ensuring completeness when needed.
Solution Approach 2:
The DQP signaling is applied locally based on the specific characteristics of each LCU - it is included only in LCUs that contain non-zero transform coefficients. This local quality approach ensures that DQP is transmitted with the appropriate granularity, avoiding unnecessary bit transmission in LCUs where it would not be used.
Data Source
AI summary
By implementing a new bitstream for a Delta-Quantization Parameter (DQP), a decoder is able to implement parallel decoding of multiple coding units within a largest coding unit. In some embodiments, the DQP is placed immediately after the mode information of the first coding unit. In some embodiments, the DQP is placed after the mode information of the first non-skipped coding unit. In some embodiments, the DQP is placed after the first non-zero coded block flag.