MPEG2 Stream Scrambling via PID and TSC Header Modification
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Solution Overview
Problem
Existing MPEG2 video transport stream scrambling methods are inadequate for managing mixed streams containing both scrambled and unscrambled services, leading to suboptimal processing and potential double scrambling of conditional access services, especially in satellite transmission where exact service state changes are not always known in real-time.
Innovation Solution
A method for over-scrambling MPEG2 streams involves modifying packet headers by reading original PID and TSC bits, writing temporary PIDs and resetting TSC bits to 00, and then scrambling the stream, allowing for flexible management of service scrambling independent of the complete stream, with corresponding descrambling methods to restore the original stream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the entire MPEG2 stream is scrambled without considering individual service states, then the scrambling process is simplified and easier to implement, but services that are already scrambled may be double-scrambled, causing processing errors and service disruptions
Solution Approach 1:
The patent applies local quality by treating different services differently based on their scrambling state. The system identifies whether each service is already scrambled or not, and applies scrambling only to unscrambled services. This is achieved by examining the TSC (Transport Scrambling Control) bits in the packet header for each service, allowing the scrambler to selectively process only the necessary services without double-scrambling already-encrypted content.
Solution Approach 2:
The patent implements preliminary action by checking the scrambling state of services before applying the scrambling process. The system examines the TSC bits in advance to determine which services need scrambling and which do not, preventing double-scrambling of conditional access services while ensuring unscrambled services are properly encrypted.
2Reliability
If conditional access services are selectively scrambled based on their state, then double scrambling is avoided, but the scrambling system becomes more complex and requires additional processing logic
Solution Approach 1:
The patent applies self-service by using the existing TSC bits in the MPEG2 packet header to automatically determine the scrambling state of each service. The system leverages the current stream metadata to make decisions about processing, eliminating the need for external state information or complex manual configuration. The scrambler reads the TSC bits, determines whether scrambling is needed, and acts accordingly without requiring additional control mechanisms.
3Productivity
If the scrambling state changes are detected and processed in real-time, then service continuity is maintained, but processing delays increase due to the time required to detect and respond to state changes
Solution Approach 1:
The patent applies continuity of useful action by maintaining continuous monitoring of service scrambling states throughout the stream. The system processes TSC bits and continuity counters in real-time as packets arrive, making decisions about scrambling immediately rather than waiting for state change detection. This continuous processing approach minimizes delays and maintains service continuity by ensuring that scrambling decisions are made promptly based on the current stream state.
Data Source
AI summary
A scrambling and descrambling method that includes reading of original PID and TSC bits in the PID and TSC fields of a packet header of an MPEG2 stream which is at least partially scrambled. A temporary PID may be written in a PID field in place of the original PID, and may be a function of the original PID value and TSC bits according to a correspondence table of an original PID and TSC bits with the temporary PIDs. The value zero may be written in the TSC field in place of the original value, and scrambling of the stream with modified fields may occur. Applications include the satellite transmission of partially scrambled MPEG2 digital signals.