Intermodal Video Transcoder Using Precomputed Prediction Errors
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Solution Overview
Problem
Existing video signal encoding and transcoding technologies face inefficiencies in converting between different compression modes, such as H.264 and HEVC, due to redundant computational processes and high complexity in rate distortion cost calculations, which affect the fidelity and bit rate of video signals.
Innovation Solution
A fast intermodal transcoder is developed using a novel motion propagation process and a fast mode decision process that eliminates redundant motion estimation and early terminates complex computations by pre-computing prediction errors at the CTU level and reusing them for various partition sizes, along with a recursive split decision method to optimize motion-based split decisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional transcoding methods are used to convert between H.264 and HEVC formats, then video signal conversion is achieved, but computational redundancy and complexity increase significantly
Solution Approach 1:
The patent performs preliminary motion estimation at the macroblock level during the H.264 decoding phase, storing these motion vectors for later reuse. This preliminary action eliminates the need to perform redundant motion estimation at the CTU level during HEVC encoding, significantly reducing computational complexity while maintaining transcoding efficiency
Solution Approach 2:
The patent segments the video processing into distinct phases: H.264 macroblock-level processing, intermediate motion vector storage, and HEVC CTU-level processing. This segmentation allows independent optimization of each phase and enables the reuse of intermediate results, reducing overall computational redundancy
2Measurement precision
If motion estimation is performed at both macroblock and CTU levels, then accurate motion compensation is achieved, but redundant computations increase processing time
Solution Approach 1:
Motion estimation is performed preliminarily at the macroblock level during H.264 decoding, and these results are reused during HEVC encoding. This eliminates redundant motion estimation computations while preserving accuracy, as the same motion vectors are applied across both compression formats
Solution Approach 2:
The patent discards the format-specific details of motion vectors during transcoding but recovers and reuses the underlying motion compensation information. By storing intermediate motion vectors and reusing them across format conversions, the system avoids redundant computations while maintaining estimation accuracy
3Manufacturing precision
If rate distortion cost computation is performed completely for all partition sizes, then optimal encoding decisions are made, but computational complexity increases
Solution Approach 1:
The patent performs rate distortion cost computation partially by evaluating only the most promising partition sizes based on preliminary criteria. Instead of exhaustively computing costs for all possible partition sizes, the system applies partial evaluation to sufficient cases to make optimal encoding decisions while reducing computational complexity
Solution Approach 2:
The patent changes the evaluation parameters by using simplified cost functions for preliminary partition size assessment. This allows the system to quickly eliminate suboptimal partitions before performing detailed rate distortion analysis, reducing overall computation while maintaining encoding optimization accuracy
Data Source
AI summary
A video intermodal transcoder converts a compressed bitstream formulated according a type-1 compression scheme to a type-2 compressed bitstream formulated according to a type-2 compression scheme. The transcoder includes an augmented type-1 decoder, a transcoder kernel, and an augmented type-2 encoder. The transcoder kernel performs processes of creating motion-vector candidates and pre-computing prediction errors for each cell of a predefined image coding block and for each candidate motion vector for repetitive use in evaluating various image partitions. In an implementation where the type-1 compression scheme follows the H.264 standard and the type-2 compression scheme follows the HEVC standard, the transcoder exploits the flexibility of the coding-tree structure and other HEVC features to significantly reduce the bit rate of the compressed bit stream. The pre-computation of prediction errors significantly reduces the processing effort, hence increases the throughput of the transcoder.