PVR Trick Mode NAV Table Reduces Processor Load
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Solution Overview
Problem
Personal Video Recording (PVR) systems face challenges in efficiently implementing trick modes, such as smooth-motion rewind and maintaining frame-accurate access to MPEG streams without overburdening the central processor, especially when dealing with encrypted streams and variable data skipping during playback.
Innovation Solution
A method and apparatus that capture stream-navigation data to generate a frame-correlated Navigation (NAV) table during recording, which is used to create command packets for efficient decoding and display of selected frames during playback in user-selected trick modes, reducing the processing load on the host processor and maintaining content rating and encryption states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PVR system performs real-time analysis of encrypted MPEG streams during playback to maintain content rating and encryption states, then the system can maintain security and compliance, but the central processor becomes overburdened and playback performance degrades
Solution Approach 1:
The system performs stream analysis and generates NAV tables during the recording phase rather than during playback. The data transport processor captures stream-navigation data including content rating and encryption information, and the host processor pre-processes this data to create frame-correlated NAV tables before playback occurs. This preliminary action transfers the processing burden from playback to recording, allowing smooth trick mode operations during playback without overburdening the processor.
2Ease of operation
If the PVR system implements smooth-motion rewind or progressive-refresh MPEG streams, then the user experience improves, but special processing by the MPEG decoder is required and system complexity increases
Solution Approach 1:
The NAV table is pre-generated during recording with all necessary frame correlation data, start code positions, and stream-navigation information. This pre-computed navigation data allows the MPEG decoder to perform simple table lookups during trick mode playback rather than complex real-time stream analysis, significantly reducing decoder processing requirements while maintaining smooth motion rewind and progressive-refresh capabilities.
Solution Approach 2:
The NAV table acts as an intermediary data structure that bridges the MPEG stream and the decoder. It contains pre-computed frame correlation information, start code positions, and navigation data that simplifies the decoder's task during trick modes. The NAV table mediates between the complex MPEG stream structure and the decoder's processing requirements, enabling smooth trick mode operation without burdening the decoder with complex real-time analysis.
3Speed
If the PVR system skips variable amounts of MPEG stream data during trick modes, then fast-forward and rewind capabilities improve, but maintaining correct encryption and content rating states becomes difficult
Solution Approach 1:
The system captures stream-navigation data during recording that includes content rating and encryption information correlated with specific frames. The host processor pre-processes this data to create NAV tables that maintain the relationship between frames and their associated encryption/content rating states. During trick mode playback, even when skipping variable amounts of data, the system can retrieve the correct encryption and content rating states from the pre-computed NAV table for any target frame, ensuring reliability while enabling fast playback.
Data Source
AI summary
A method and apparatus are disclosed for facilitating efficient operation of trick modes in a personal video recording (PVR) system. Stream-navigation data from a data stream is captured and pre-processed to generate a frame-correlated NAV table comprising one entry for each frame within the data stream, during recording of the data stream. The stream-navigation data comprises start code data, content rating data, and conditional access data that is embedded in the data stream. During playback of the data stream in a user-selected trick mode, the frame-correlated NAV table is used to generate command packets that are sent to a data decoder along with selected frames of the data stream. The selected frames are decoded based on information in the command packets and certain selected frames may be displayed as part of the trick mode.