Differential Time Stamps for Video Encoding
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Solution Overview
Problem
Conventional video coding standards, such as MPEG-2, struggle to efficiently represent and encode variable inter-picture display and decoding times, which is necessary for dynamic frame rates and mixed picture types, due to the complexity and bit overhead of precise time stamping.
Innovation Solution
The use of differential values to represent display and decoding times, optionally encoded using entropy methods like Universal Variable Length Code (UVLC), allows for flexible representation and encoding of time intervals, applicable to both fixed and variable intervals, and compatible with standards like MPEG-4 AVC and MPEG-2 Systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If presentation time stamps (PTS) or decoding time stamps (DTS) are encoded for every picture to support variable inter-picture display intervals, then measurement precision of display times is improved, but device complexity and bit overhead increase significantly
Solution Approach 1:
The time stamp representation is segmented into two parts: a base time value (from the previous picture's timestamp) and a differential value (the difference from the previous timestamp). This segmentation allows the system to maintain precise time measurement while encoding only the small differential changes, reducing bit overhead and complexity.
Solution Approach 2:
Instead of encoding absolute time stamps for each picture, the invention inverts the approach by encoding the difference (differential) from the previous timestamp. This inversion transforms the problem from encoding large absolute values to encoding small differential values, significantly reducing the number of bits required.
2Measurement precision
If absolute presentation time stamps are encoded for every picture, then measurement precision of display times is improved, but loss of information increases due to the large number of bits required
Solution Approach 1:
The invention inverts the encoding approach by representing time stamps as differential values relative to the previous picture's timestamp rather than encoding absolute time values. This inversion dramatically reduces the number of bits required to represent each timestamp while maintaining the same temporal precision, thereby reducing bit overhead in the video bitstream.
Solution Approach 2:
The invention changes the parameter representation from absolute time values to differential time values. By encoding the difference between consecutive timestamps rather than the absolute timestamps themselves, the system maintains precise time measurement capability while significantly reducing the bit rate required to transmit timing information.
3Adaptability or versatility
If conventional time stamping methods are used to support variable frame rates, then adaptability to different frame rates is improved, but device complexity increases due to precise time specification requirements
Solution Approach 1:
The invention implements dynamic time interval representation where the differential timestamp values can vary freely to accommodate changing frame rates. Instead of being constrained by fixed frame rate structures, the system dynamically adjusts the time intervals between pictures by encoding the actual differential values observed in the variable frame rate sequence, maintaining adaptability while reducing complexity.
Solution Approach 2:
By changing from absolute time parameter encoding to differential time parameter encoding, the system gains the ability to naturally represent variable frame rates without complex control mechanisms. The differential values automatically adapt to any frame rate changes, simplifying the time specification process while maintaining full versatility for variable frame rate content.
Data Source
AI summary
Systems and methods that use differential values to represent decoding and presentation times of pictures are provided. Optionally, some of the systems or the methods may use an entropy coding method such as, for example, the Universal Variable Length Code (UVLC) for the differential time stamps.