BD-ROM Substream Random Access via Pre-computed Entry Maps
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Solution Overview
Problem
Synchronous applications face delays in playback due to insufficient random access capabilities for substreams, which are not as efficiently decodable as main streams, leading to delayed response to user requests for playback operations like fast-forwarding and rewinding.
Innovation Solution
A recording medium with playlist information and an entry map that designates entry points on substreams for high-speed random access, allowing synchronous playback with main streams by indicating entry points at constant time or data intervals, reducing the need for excessive stream analysis and improving playback device response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If substreams are distributed via Internet without GOP structure, then flexibility in movie variations is improved, but random access speed deteriorates
Solution Approach 1:
The patent pre-calculates and records entry points (random access points) in the PlayList information before playback. These entry points are determined in advance based on time codes and stream analysis, allowing the playback device to directly jump to the correct position in the substream without real-time analysis, thus achieving fast random access while maintaining flexibility.
Solution Approach 2:
The PlayList information acts as an intermediary between the user's random access request and the actual substream data. It contains pre-computed entry points that map time codes to specific positions in the substream, mediating the access process and eliminating the need for the playback device to perform complex stream analysis during trick play operations.
2Adaptability or versatility
If substreams lack independent decodable units like GOPs, then data flexibility is improved, but playback start delay increases
Solution Approach 1:
The system performs stream analysis in advance during the playlist creation phase to identify suitable entry points in the substream. These entry points are stored in the PlayList information, enabling the playback device to immediately start playback from the correct position without performing time-consuming stream analysis during user-initiated trick play operations.
3Measurement precision
If stream analysis is performed for every random access request, then access precision is improved, but response time deteriorates
Solution Approach 1:
The patent creates a copy of the essential access information (entry points mapping time codes to stream positions) in the PlayList information. Instead of performing stream analysis on the actual substream data during each random access operation, the playback device simply retrieves the pre-computed entry points from the PlayList, achieving fast and precise access without repeated analysis.
Data Source
AI summary
A BD-ROM stores PlayList information. The PlayList information defines a playback section of each of a plurality of AV clips and includes MainPath information and SubPath information. The MainPath information designates one of the AV clips as a Main Clip and defines a portion of the Main Clip as a primary playback section. The SubPath information designates another one of the AV clips as a SubClip and defines a portion of the SubClip as a secondary playback section that is to be played back in synchronism with the primary playback section. The BD-ROM stores, the one of the AV clips designated as the SubClip along with an EP_map. The EP_map shows a plurality of entry points on the SubClip in a one-to-one correspondence with entry times on the SubClip timeline.