Non-Relative Presentation Time Mapping for MPEG-2 Random Access
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Solution Overview
Problem
Existing systems for providing random access to time-synchronized data streams, such as MPEG-2 systems, face challenges in accurately accessing specific points in time, especially when dealing with encoded and encrypted content, as they typically rely on relative presentation times rather than non-relative times, limiting efficient decoding and utilization.
Innovation Solution
The method involves mapping a user's request for a non-relative presentation time (NPT) to a corresponding presentation time stamp (PTS) using additional system timing information, determining a stream access point, and decoding the stream from that point until the presentation time exceeds the desired time, allowing for efficient access and utilization of the content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If relative presentation time methods are used for random access, then system compatibility with existing MPEG-2 systems is maintained, but access precision and efficiency for specific time points deteriorates
Solution Approach 1:
The patent introduces a time mapping table as an intermediary data structure that stores the relationship between non-relative presentation times (NPT) and system time clock values (STC). This mapping table acts as a mediator that translates user-friendly non-relative time requests into precise stream access points, thereby maintaining both system compatibility and access precision simultaneously
Solution Approach 2:
The system pre-generates and stores a time mapping table that contains pre-calculated relationships between non-relative presentation times and corresponding stream positions. By performing this time mapping preparation in advance rather than calculating it in real-time during access operations, the system achieves both compatibility with existing MPEG-2 infrastructure and precise random access capability
2Productivity
If non-relative presentation time mapping is implemented, then random access precision and efficiency improves, but system complexity and processing requirements increases
Solution Approach 1:
The time mapping table is pre-computed and stored during content encoding or pre-processing phases. This preliminary action transfers the computational burden from runtime access operations to offline preparation, thereby improving access efficiency during actual use while managing system complexity by performing complex operations only when necessary
Solution Approach 2:
The patent extracts the time mapping functionality as a separate, independent data structure (the time mapping table) from the main decoding pipeline. This extraction allows the complex time mapping logic to be handled independently through table lookups, reducing the complexity burden on the real-time decoding system while maintaining high access efficiency
3Measurement precision
If stream decoding is performed from access point to desired time, then accurate time-synchronized content delivery is achieved, but decoding time and processing duration increases
Solution Approach 1:
The system pre-calculates and stores the exact stream access points corresponding to desired presentation times in the time mapping table. By having these access points pre-determined, the decoder can jump directly to the correct position in the stream without unnecessary decoding of intermediate frames, thereby achieving accurate time synchronization while minimizing actual decoding time
Solution Approach 2:
The patent enables the decoder to skip directly to pre-calculated access points in the encoded stream based on the time mapping table. This skipping mechanism allows the system to rush through irrelevant portions of the stream and decode only the necessary content at the precise time point requested, reducing overall decoding time while maintaining time synchronization accuracy
Data Source
AI summary
A method for accessing a desired point in time-synchronized data within a stream, the stream being associated with time information, the method including providing a desired presentation time associated with a desired point within a time-synchronized data stream, determining a stream access point, decoding the stream beginning at the stream access point, and assigning a time associated with the stream access point as a utilization time. Related apparatus and methods are also disclosed.