Video Encoder Coefficient Bitdepth Limitation for H.264V2 Compliance
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Solution Overview
Problem
Conventional encoders do not specify a 16-bit limit on coefficients, leading to potential overflows in bitstreams compliant with earlier drafts of H.264-AVC Fidelity Range Extensions, which can result in non-compliant bitstreams exceeding 15-bit plus a sign bit, posing challenges in ensuring compliance with ITU-T Revised Rec. H.264(E):2005 for video compression.
Innovation Solution
A method for coefficient bitdepth limitation in encoders and bitstream generation apparatus that generates residual block coefficients and manipulates coding parameters such as qP and weightscale to prevent values from exceeding the bitdepth plus a predefined number of bits, ensuring compliance by clipping coefficients and controlling macroblock modes to avoid overflows, thereby producing H.264V2 compliant bitstreams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional encoders do not specify a 16-bit limit on coefficients, then encoding flexibility is maintained, but bitstream overflow occurs exceeding 16-bit compliance
Solution Approach 1:
The patent applies parameter changes by manipulating coding parameters (qP, weightscale, bitrate, macroblock mode) to control the range of coefficient values. By adjusting these parameters, the encoder ensures that residual block coefficients remain within the 16-bit limit while maintaining encoding flexibility for different video quality requirements.
Solution Approach 2:
The patent extracts and limits the coefficient values to a specific range (16-bit compliance) through coefficient clipping. This separates the coefficient generation process from the final bitstream output, allowing the encoder to generate coefficients and then apply a clipping operation to ensure compliance, thus resolving the contradiction between flexibility and reliability.
2Reliability
If coefficient clipping is applied to prevent overflows, then bitstream compliance is ensured, but encoding fidelity may be reduced
Solution Approach 1:
The patent applies partial clipping by selectively limiting coefficients only when they exceed the 16-bit threshold. Most coefficients that fall within the acceptable range are left unchanged, applying the clipping operation only partially where necessary. This minimizes the impact on encoding fidelity while ensuring compliance for the problematic out-of-range coefficients.
Solution Approach 2:
The patent manipulates coding parameters such as qP (quantization parameter) and weightscale to control the distribution of coefficient values. By adjusting these parameters, the encoder can shift the coefficient distribution to reduce the number of values exceeding the 16-bit limit, thereby reducing the need for clipping and preserving encoding fidelity while maintaining compliance.
3Reliability
If multiple coding parameters are manipulated to prevent overflows, then compliance control is improved, but encoder complexity increases
Solution Approach 1:
The patent applies preliminary action by setting constraints on coding parameters (qP, weightscale, bitrate, macroblock mode) before the actual encoding process. By pre-defining the acceptable ranges for these parameters based on the 16-bit compliance requirement, the encoder avoids generating out-of-range coefficients in the first place, simplifying the overall process compared to post-processing corrections.
Solution Approach 2:
The patent implements feedback by monitoring the coefficient values generated during encoding and adjusting coding parameters accordingly. When coefficients approach the 16-bit limit, the encoder feedback-adjusts parameters like qP or weightscale to bring future coefficients within the compliant range, creating a closed-loop control system that manages complexity through adaptive parameter adjustment.
Data Source
AI summary
A method for coefficient bitdepth limitation in an encoder and/or bitstream generation apparatus including the steps of (A) generating one or more residual block coefficients in response to a video signal and one or more coding parameters and (B) manipulating the one or more coding parameters such that the one or more residual block coefficients are prevented from having values greater than a bitdepth of the video signal plus a predefined number of bits.