Partially Aligned IRAP Access Units for Video Bitstream Splicing
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Solution Overview
Problem
Current video coding standards lack mechanisms to support simple random access and splicing operations at access units that do not have all pictures as intra random access point (IRAP) pictures, leading to difficulties in correctly decoding higher layer pictures until an IRAP layer component occurs.
Innovation Solution
The introduction of partially aligned IRAP access units, where some layer components are IRAP pictures and others are not, allowing for indication of non-decodable pictures and specifying a decoding process to handle such scenarios, enabling random access and bitstream splicing even when not all pictures in an access unit are IRAP.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all pictures in an access unit are required to be IRAP pictures to support random access, then decoding reliability is improved, but device complexity and bitrate increase due to redundant encoding
Solution Approach 1:
The patent applies local quality by differentiating the IRAP picture requirement by layer: the base layer is required to contain an IRAP picture to ensure random access capability, while enhancement layers may contain non-IRAP pictures to reduce coding complexity and bitrate. This selective application of the IRAP requirement to specific layers resolves the contradiction between decoding reliability and coding efficiency.
2Quantity of substance
If non-IRAP pictures are included in access units with IRAP pictures, then bitrate is reduced, but decoding correctness deteriorates until an IRAP layer component occurs
Solution Approach 1:
The patent segments the access unit into distinct layer components (base layer and enhancement layers) with different IRAP picture requirements. The base layer IRAP picture serves as a reliable reference point, while enhancement layer pictures can be non-IRAP to reduce bitrate. This segmentation allows the system to achieve lower bitrate while maintaining decoding correctness through the layered structure where lower layers provide the necessary reference for higher layers.
3Loss of time
If random access is supported at non-aligned access units, then tune-in delay is reduced, but decoding complexity increases due to non-decodable pictures
Solution Approach 1:
The patent uses preliminary action by signaling the non_decodable_pic_flag in advance during bitstream encoding. This flag预先 indicates which pictures in enhancement layers are not decodable when random access is performed at non-aligned access units. The decoder can use this pre-provided information to skip decoding of non-decodable pictures, thereby reducing tune-in delay while avoiding the complexity of attempting to decode pictures that cannot be correctly decoded.
4Productivity
If enhancement layers use non-IRAP pictures in partially aligned access units, then coding efficiency is improved, but adaptability deteriorates for random access operations
Solution Approach 1:
The patent applies dynamics by making the IRAP picture requirement flexible and adaptive based on layer type and access unit alignment. The base layer maintains the IRAP picture requirement to ensure random access capability, while enhancement layers dynamically adjust to use non-IRAP pictures when coded in partially aligned access units. This dynamic approach allows the system to optimize coding efficiency for enhancement layers while preserving random access adaptability through the base layer and proper signaling mechanisms.
Data Source
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AI summary
In one example, a device for coding video data includes a video coder configured to code an intra random access point (IRAP) picture of a partially aligned IRAP access unit of video data, and code data that indicates, when performing random access from the partially aligned IRAP access unit, at least one picture of a video coding layer that is not correctly decodable. When the video coder comprises a video decoder, the video decoder may skip decoding of the pictures that are not correctly decodable, assuming random access has been performed starting from the partially aligned IRAP access unit.