Encoder GOP Synchronization via PTS Remainder Calculation
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Solution Overview
Problem
In cable-TV headends, direct transmission of raw signals to customer premise equipment is wasteful and lacks adaptive bit rate, necessitating encoders or transcoders to standardize video and audio codecs, while ensuring identical GOP structures across multiple encoders for failover protection without communication between them.
Innovation Solution
The system decodes source video content streams into uncompressed frames with associated presentation time stamps, calculates clock cycles between IDR-frames, and marks frames as IDR or internal within a GOP to produce synchronized output streams with identical GOP structures, ensuring identical IDR-frames and internal frames across multiple encoders, even if they are not in communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple encoders are deployed to provide adaptive bit rate streaming, then network resource efficiency and streaming reliability are improved, but ensuring identical GOP structures across encoders becomes complex without communication between them
Solution Approach 1:
Each encoder independently determines IDR-frame positions by calculating remainders of its own output frame counters divided by the GOP size, without needing to communicate with other encoders. This self-service mechanism ensures all encoders produce identical GOP structures autonomously
Solution Approach 2:
The system uses the GOP size as a key parameter that, when divided into the encoder output frame counter, automatically synchronizes IDR-frame placement across multiple encoders. By changing or adjusting the GOP size parameter, the synchronization behavior of all encoders is simultaneously modified
2Productivity
If encoders operate independently without communication, then system simplicity and resource utilization are improved, but synchronizing IDR-frames and GOP structures across encoders becomes difficult
Solution Approach 1:
All encoders use the identical GOP size value ( copied from a standardized configuration) to determine IDR-frame positions. This copying of the same parameter value across all encoders ensures they generate identical GOP structures independently, without needing to exchange information
Solution Approach 2:
The GOP size is predetermined and configured in advance for all encoders before they begin operation. This preliminary setup of the synchronization parameter enables encoders to automatically produce consistent GOP structures from the start, without requiring real-time coordination
Data Source
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AI summary
A video distribution system synchronizes video output streams on multiple encoders without communication therebetween. Each of the encoders is configured to decode a source video content stream into a sequence of uncompressed frames, where each frame in the sequence is marked with an associated presentation time stamp (PTS) clock value. The encoders calculate a number of clock cycles between instantaneous decoder refresh (IDR)-frames. For each frame in the sequence, the encoders calculate a remainder after a division of an associated PTS clock value of a given frame by the number of clock cycles between IDR-frames. The encoders mark each frame in the sequence as an IDR-frame where the corresponding remainder is strictly less than the number of PTS clock cycles per frame and mark a remainder of the frames in the sequence as an internal frame within a group of pictures (GOP) to produce a marked set of video frames. The encoders pass the marked set video frames through a video codec to produce the synchronized video output streams.