Video Decoder Subtitle Synchronization via Reconstructed PTS
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Solution Overview
Problem
Digital television decoders face challenges in synchronizing video and subtitle data when reading from a storage space, as subtitle data often lacks presentation time stamps, leading to inconsistencies in display and increased delays, especially in idle mode.
Innovation Solution
A decoder system with a local clock and buffer memories generates a presentation time stamp for subtitle data packets using the last received PCR time reference, ensuring synchronization with the system time clock, even without initial PTS time stamps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If subtitle data is decoded immediately without buffering from storage space, then decoding speed is improved, but synchronization with video data deteriorates due to missing PTS time stamps
Solution Approach 1:
The patent applies preliminary action by generating presentation time stamps (PTS) for subtitle packets in advance, before they are decoded and displayed. The system reconstructs PTS values using PCR time references and buffer delay measurements, so that when subtitles are immediately decoded from storage, they already have the necessary synchronization information embedded. This resolves the contradiction by preparing synchronization data beforehand, enabling both fast decoding and accurate synchronization.
2Reliability
If video decoding buffer size is increased to maintain synchronization, then synchronization reliability is improved, but display delay increases
Solution Approach 1:
The patent changes the parameter approach by shifting from adjusting buffer sizes to dynamically calculating PTS values based on actual buffer delay measurements. Instead of increasing buffer capacity to maintain synchronization, the system measures the actual delay introduced by the video decoding buffer and uses this measurement to adjust the PTS values of subtitle packets accordingly. This resolves the contradiction by maintaining small buffers while achieving synchronization through parameter adjustment rather than volume increase.
3Reliability
If subtitle data is buffered to match video decoding timing, then synchronization is improved, but decoding speed and responsiveness deteriorate
Solution Approach 1:
The patent introduces an intermediary mechanism - the reconstructed PTS generation system - that acts as a mediator between the subtitle data stream and the video synchronization timeline. Instead of buffering subtitle data to match video timing, the system inserts a PTS generation layer that translates subtitle packet arrival times into accurate presentation timestamps using PCR references and measured buffer delays. This intermediary allows immediate subtitle decoding while maintaining synchronization, resolving the contradiction between speed and reliability.
Data Source
AI summary
A decoder includes a storage space that records video data and subtitle data in multiplexed form; a first buffer memory operating in “First In First Out” mode and able to temporarily contain the video data in packet form; a second buffer memory operating in “First In First Out” mode and able to temporarily contain the subtitle data in packet form; a demultiplexer configured to transmit the video data and subtitle data respectively to the first and second buffer memories; and a local clock, wherein the storage space includes a storage space configured to store the time references such that the demultiplexer transmits the time references, the decoder including a generator to generate a presentation time stamp associated with each subtitle data packet not initially containing a presentation time stamp, the presentation time stamp being determined from a time reference value transmitted by the demultiplexer and enabling the presentation of the subtitle data packets to be synchronized with relation to the local clock.