Adaptive Frame Rate Video Transcoder
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Solution Overview
Problem
Existing video transcoding methods face challenges in efficiently converting high bit rate MPEG-2 video streams to lower bit rate MPEG-4 video streams while maintaining quality and complexity constraints, particularly in real-time applications.
Innovation Solution
The method employs an adaptive frame rate and joint temporal-spatial rate control technique, down-sampling motion vectors and frame pixels, and adjusting picture or frame rate and quantization step size to achieve a good quality tradeoff, using a T2 transcoder architecture that reuses motion vectors and selectively skips B frames to optimize bit allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional video transcoding methods are used to convert high bit rate MPEG-2 video streams to lower bit rate MPEG-4 video streams, then bit rate reduction is achieved, but video quality deteriorates and computational complexity increases
Solution Approach 1:
The patent implements dynamic frame rate adjustment and adaptive quantization parameter modification during transcoding. The system dynamically selects which frames to transcode and at what quality level, rather than applying uniform processing to all frames. This dynamic approach allows bit rate reduction while preserving video quality by adapting processing intensity to local video characteristics and buffer conditions.
Solution Approach 2:
The patent changes multiple parameters simultaneously including frame rate, quantization parameters, and motion vector precision. By jointly adjusting these parameters rather than changing only bit rate, the system achieves efficient compression while maintaining perceptual video quality. The adaptive modification of quantization parameters allows finer control over quality distribution across different video segments.
2Quantity of substance
If conventional video transcoding methods are used to convert high bit rate MPEG-2 video streams to lower bit rate MPEG-4 video streams, then bit rate reduction is achieved, but computational complexity increases
Solution Approach 1:
The patent extracts and reuses motion vectors from the input MPEG-2 bit stream rather than performing complete motion estimation. By taking out only the essential motion information needed for transcoding and discarding redundant data, the system significantly reduces computational complexity while maintaining transcoding efficiency. This selective extraction approach avoids the heavy computational burden of full motion estimation in the MPEG-4 encoder.
Solution Approach 2:
The patent applies partial action by selectively transcoding only certain frames (I-frames and selected P-frames) while skipping or simplistically processing B-frames and less important P-frames. This partial processing approach reduces computational complexity by performing full transcoding only where necessary for quality and reference purposes, while using lighter processing for other frames.
3Quantity of substance
If frame rate is reduced during transcoding to achieve lower bit rate, then bit rate is reduced, but temporal resolution and video quality deteriorate
Solution Approach 1:
The patent implements dynamic frame rate adjustment where the output frame rate is adapted based on buffer fullness, video complexity, and quality requirements. Rather than applying a fixed frame rate reduction, the system dynamically decides whether to transcode each input frame and at what output timing, preserving temporal resolution in important segments while achieving bit rate reduction in others.
Solution Approach 2:
The patent jointly adjusts frame rate and quantization parameters as coupled variables rather than independent controls. When frame rate is reduced, quantization parameters are adaptively modified to compensate for the loss in temporal resolution, maintaining overall video quality. This coordinated parameter change ensures that bit rate reduction does not linearly translate to quality deterioration.
4Quantity of substance
If quantization step size is increased to achieve lower bit rate, then bit rate is reduced, but spatial resolution and video quality deteriorate
Solution Approach 1:
The patent applies different quantization step sizes to different regions and frames based on their importance and complexity. Rather than using a uniform quantization parameter for all video data, the system selectively applies coarser quantization to less important segments (such as B-frames or low-complexity scenes) while maintaining finer quantization for important segments, preserving spatial resolution where needed while achieving bit rate reduction overall.
Solution Approach 2:
The patent adaptively modifies quantization parameters based on local video characteristics, buffer conditions, and quality requirements. The quantization step size is dynamically adjusted rather than fixed, allowing the system to achieve bit rate reduction through intelligent parameter selection rather than uniform quality degradation. This adaptive approach maintains spatial resolution in critical areas while reducing bit rate in others.
Data Source
AI summary
A video transcoding method is provided for transcoding a first signal stream compressed by a first coding scheme to a second signal stream compressed by a second coding scheme. The method employs an adaptive frame rate and a joint temporal-spatial rate control technique, such that the overall quality of compressed MPEG video can be significantly enhanced when the transcoding is controlled in the joint temporal (picture or frame rate) and spatial (quantization) domains. One embodiment considers transcoding from high bit rate video with larger image size (e.g. 4CIF/4SIF, CIF) coded by one coding technique, e.g., MPEG-2 to a lower bit rate video with smaller image size (e.g. CIF, QCIF) coded by the same or another coding technique, e.g., MPEG-4.