Encrypted MPEG-2 Splicing via Pre-conditioned Cue Messages
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Solution Overview
Problem
Traditional MPEG splicing techniques require PES packets to be in the clear, making it impossible to splice encrypted MPEG streams, leading to issues like lip sync problems and decoder buffer model violations.
Innovation Solution
A pre-conditioning encoder inserts SCTE-35 cue messages and encodes video and audio streams to create Random Access Points, allowing seamless splicing of encrypted MPEG-2 Transport Streams by aligning audio and video frames within PES packets, maintaining decoder buffer compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional splicing techniques are used on encrypted MPEG streams, then security is improved, but splicing capability deteriorates (cannot splice)
Solution Approach 1:
The encoder performs pre-conditioning actions before encryption by inserting SCTE-35 cue messages and creating Random Access Points (RAPs) at specific locations in the bitstream. This preliminary structuring allows the splicer to identify valid splice points and perform seamless splicing on encrypted streams without needing to decrypt the content first.
2Reliability
If splicing is performed on encrypted streams without pre-conditioning, then security is maintained, but audio-video synchronization deteriorates (lip sync problems)
Solution Approach 1:
The encoder pre-conditions the audio and video streams by aligning their frame structures and inserting synchronization markers (SCTE-35 cue messages) before encryption. This ensures that when splicing occurs on the encrypted stream, the audio and video frames remain properly synchronized without causing lip sync issues.
Solution Approach 2:
The encoder modifies the temporal parameters of audio and video frames by adjusting their presentation timestamps (PTS) and decoding timestamps (DTS) to ensure proper alignment. This parameter adjustment maintains audio-video synchronization throughout the splicing process even when content is encrypted.
3Reliability
If traditional splicing modifies frame sizes to comply with decoder buffer model, then decoder compliance is improved, but stream integrity deteriorates (requires clear content)
Solution Approach 1:
The encoder pre-conditions the stream by inserting RAPs and adjusting decoder buffer parameters before encryption. This allows the splicer to maintain decoder buffer compliance through timestamp adjustments rather than frame modification, preserving the integrity of the encrypted content.
Solution Approach 2:
The invention replaces the traditional mechanical approach of modifying frame sizes and content with a signal-based approach using SCTE-35 cue messages and timestamp adjustments. This substitution allows compliance with the decoder buffer model without altering the actual encrypted video frames, maintaining stream integrity.
Data Source
AI summary
System and method for performing a splice operation on an encrypted or unencrypted MPEG-2 transport stream. A splice trigger is received at a pre-conditioning encoder. In response, the encoder generates, e.g., an SCTE-35 cue message that is intended to be received by a splicer. Also in response to the splice trigger, the encoder encodes/conditions a network feed such that a decoder buffer delay reaches a predefined value at a video frame of the network feed that corresponds to a splice point indicated by the SCTE-35 cue message. The network feed may then be encrypted in a known fashion. At the splicer, another feed is switched into the stream at the splice point, wherein the another feed is encoded such that a decoder buffer delay at a video frame of the another feed corresponding to the splice point is the same as the predefined value. The predefined value is defined as DTS-STC, where DTS is a Decoding Time Stamp and STC is a System Time Clock. The pre-conditioning encoder generates around the splice point audio PES packets that contain a single aligned audio frame.