Selective Encryption for Digital Video Trick Play
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Solution Overview
Problem
Traditional encryption techniques make trick play of digital video content impossible, as content needs to be decrypted to access I, P, and B frames, which is not feasible for encrypted content, especially when delivered to personal-video-recorder enabled set-top boxes.
Innovation Solution
Selective encryption method that leaves packets containing Start of Frame (SOF) headers unencrypted, while encrypting other sensitive information, allowing trick play by calculating offsets for I and P frames and storing them in an offset table, ensuring secure and efficient playback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional encryption techniques are applied to digital video content, then security is improved, but trick play capability deteriorates because content must be decrypted to access I, P, and B frames
Solution Approach 1:
The patent segments the digital video content into two distinct parts: encrypted portions (video data, audio data, and PSI/SI information) and unencrypted portions (SOF headers and PAT/PMT tables). This segmentation allows trick play operations to access frame information through unencrypted SOF headers while the main content remains encrypted for security.
Solution Approach 2:
The patent applies different encryption qualities to different parts of the data stream. Critical metadata portions (SOF headers containing frame type and timing information, and PAT/PMT tables containing program information) are kept unencrypted to enable trick play, while the actual video and audio content is encrypted to maintain security.
2Ease of operation
If full decryption is performed to enable trick play, then trick play capability is improved, but processing time and computational resources increase
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing offset values for I frames and P frames in an offset table during content reception. These offsets are derived from unencrypted SOF headers, enabling rapid frame access during trick play without requiring decryption of the entire content stream.
Solution Approach 2:
The patent extracts critical frame information (offset positions, frame types) from the encrypted content stream by utilizing unencrypted SOF headers. This extracted information is stored separately in an offset table, allowing trick play operations to proceed without decrypting the main content, thus reducing processing time.
3Ease of operation
If selective encryption is applied to preserve SOF headers unencrypted, then trick play capability is improved, but security coverage deteriorates because some sensitive information remains unencrypted
Solution Approach 1:
The patent further segments the data within packets to encrypt only specific fields. Within SOF header packets, only non-critical fields (such as adaptation field information) are encrypted, while critical fields (frame type, timing information, offset positions) remain unencrypted. This selective field-level encryption balances security coverage with trick play capability.
Solution Approach 2:
The patent applies local quality by differentiating between critical and non-critical information within the data stream. Critical information needed for trick play (SOF header frame identification, offset positions, PAT/PMT program information) is kept unencrypted, while non-critical information (video/audio payload, adaptation field details) is encrypted to maintain security coverage.
4Productivity
If offsets are calculated and stored for rapid frame access, then trick play performance is improved, but storage requirements increase
Solution Approach 1:
The patent applies partial action by storing only essential offset information for I frames and P frames in the offset table, rather than storing complete frame data or all possible frame information. This partial storage approach provides sufficient data for trick play operations while minimizing storage requirements.
Data Source
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AI summary
Certain embodiments consistent with the present invention involve a method of selectively encrypting digital video content that involves receiving a plurality of packets containing the digital video content; identifying packets containing start of frame (SOF) headers; inserting padding into the packets containing SOF headers to move the content of the packets containing the SOF headers to a previous or subsequent packet and create padded packets containing the SOF headers; selecting certain of the packets for encryption according to a selection criterion, wherein the selected packets exclude the padded packets containing SOF headers; encrypting the selected packets; and retaining the padded packets containing the SOF headers unencrypted to form selectively encrypted digital video content. Corresponding decoding method as well as encoding and decoding apparatus are also taught. This abstract is not to be considered limiting, since other embodiments may deviate from the features described in this abstract.