Decoder Clock Offset for Fast Channel Change
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Solution Overview
Problem
Existing audio/video receiver systems experience significant channel change delays due to the time spent in extracting and buffering audio/video packets, which can be further reduced to improve user experience.
Innovation Solution
The method involves an audio/video receiver device that initializes a decoder clock with a value of the last Program Clock Reference plus an offset, where the offset is based on the drift between video and audio frames and the duration of excess data delivery during burst transmission, allowing for early reception and rendering of audio/video streams at the playout rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the receiver extracts and buffers audio/video packets from digital transmission, then the audio and video can be synchronized (lip sync), but the channel change speed becomes significantly slower
Solution Approach 1:
The system pre-loads audio and video packets into buffers before the channel change is fully initiated. During channel change, the already-buffered packets are immediately available for playback, eliminating the need to extract and buffer packets in real-time, thus maintaining synchronization while reducing channel change delay
Solution Approach 2:
The invention maintains pre-filled audio and video buffers that act as a cushion during channel changes. These buffers contain advance-loaded packets that can be played back immediately when channel change occurs, providing a time buffer that allows the system to switch channels without waiting for real-time packet extraction and buffering, thereby reducing delay while preserving sync
2Reliability
If the receiver waits to fill the reception buffer with enough audio/video packets before showing moving images, then lip-sync audio is ensured, but the channel change delay increases
Solution Approach 1:
Audio and video packets are pre-loaded into buffers before the channel change is initiated. When the channel change occurs, the receiver can immediately start playback using the pre-buffered packets, eliminating the need to wait for buffer filling during the channel change, thus reducing delay while ensuring sync is maintained
Solution Approach 2:
The system receives and buffers more audio/video packets than the minimum required for playback during the pre-load phase. This excessive buffering ensures that sufficient synchronized packets are available immediately upon channel change, allowing the receiver to start playback without waiting for the minimum buffer threshold to be reached, thereby reducing channel change delay while maintaining lip-sync
Data Source
AI summary
In a video delivery environment where a channel change in an audio/video receiver starts with a burst delivery of an audio/video stream to the receiver, characteristics of the audio/video stream are determined such as audio-video drift and burst characteristics in terms of duration of excess data delivery. At least one of these characteristics determines an offset to add to an initialization of a decoder clock, so that moving images are shown as early as possible after receipt of the channel change command, to be joined by lip synchronized audio before burst end.