Transcoder Presentation Timestamp Recovery via Embedded Audio
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Solution Overview
Problem
Existing video transcoding systems often modify presentation time stamps in an unpredictable manner, leading to synchronization issues between audio and video streams, which can result in misalignment and improper rendering of multimedia content.
Innovation Solution
A system that embeds presentation time stamps within the audio stream to maintain synchronization during transcoding, allowing for the recovery of original time stamps and adjustment to reduce jitter and align audio and video streams accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If video transcoding is performed to convert between different compression standards and bit rates, then adaptability to different user devices is improved, but presentation time stamp synchronization between audio and video streams deteriorates
Solution Approach 1:
The patent uses the audio stream as an intermediary carrier to transport the original video presentation time stamps through the transcoding process. By embedding the PTS values within audio packet data structures, the timestamps survive transcoding operations that would otherwise destroy them, enabling post-transcoding synchronization recovery.
Solution Approach 2:
The patent nests the video presentation time stamp data within the audio stream structure. Specifically, PTS values are embedded in audio packet headers or data fields, creating a hierarchical structure where video timing information is contained within the audio transport container, allowing both streams to be processed independently while maintaining temporal coordination.
2Adaptability or versatility
If presentation time stamps are modified during transcoding, then transcoding flexibility is improved, but audio-video alignment precision deteriorates
Solution Approach 1:
The patent performs preliminary embedding of the original presentation time stamps into the audio stream before the transcoding process occurs. This advance preparation ensures that the authentic timing information is preserved and available for later recovery, rather than attempting to reconstruct or estimate timestamps after transcoding has already modified them.
Solution Approach 2:
The patent creates a copy of the original presentation time stamp values and stores them within the audio stream. This copying mechanism preserves the exact timing information from the source video stream, allowing the transcoded video to be synchronized accurately to the original timing reference even though the video itself has been re-encoded.
3Measurement precision
If time stamps are extracted and embedded in audio stream, then synchronization accuracy is improved, but system complexity increases
Solution Approach 1:
The audio stream serves multiple functions simultaneously: it carries the audio content itself and also functions as a transport medium for the video presentation time stamps. This multi-functionality eliminates the need for separate timestamp preservation mechanisms, reducing overall system complexity while maintaining high synchronization accuracy.
Solution Approach 2:
The audio stream structure is utilized to carry its own timing information for the video stream. The system essentially uses existing data structures and transport mechanisms already present in the multimedia stream to solve the timestamp preservation problem, rather than introducing entirely new complex infrastructure.
Data Source
AI summary
A method for transcoding a digital video stream that includes transcoding using a transcoder a video stream that includes presentation time stamps for the video stream together with an audio stream that includes presentation time stamps for the audio stream in a manner that modifies the presentation time stamps for the video stream in a manner such that a plurality of first values for presentation time stamps for a first set of video frames of the video stream are modified to a plurality of second values for presentation time stamps for the second set of video frames. The audio stream includes embedded first values for presentation time stamps in a first location. The method includes determining an offset of the second values of the second set of presentation time stamps of the transcoded video stream based upon the first values of the set of presentation time stamps embedded in the audio stream from the transcoder. The method includes combining the transcoded video stream and an associated audio stream based upon the offset. Preferably, the transcoder also modifies the audio time stamps. Preferably, the audio stream includes the embedded first values. Preferably, the offset is determined by taking the diff between the audio PTS in the PES and the embedded PTS in the audio packet (private data or embedded in the audio frame).