Video Decoder Buffer Management for Missing RASL Pictures
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Solution Overview
Problem
Current video coding standards, such as HEVC WD9, face issues with video buffering operations when random access skipped leading (RASL) pictures are not present, leading to potential buffer overflow and incorrect decoding results due to incorrect assumptions about the presence or absence of RASL access units.
Innovation Solution
A method is introduced where a picture buffer removal time is shifted earlier based on a picture buffer removal delay offset for each clean random access (CRA) or broken link access (BLA) access unit, regardless of whether the hypothetical reference decoder (HRD) initializes at that access unit, and the selection between default and alternative initial CPB removal delay and delay offset is performed to account for missing RASL pictures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the video decoder assumes RASL pictures are present in the bitstream, then the decoding process can follow standard procedures, but buffer overflow occurs when RASL pictures are actually absent
Solution Approach 1:
The patent applies preliminary anti-action by proactively adjusting the CPB removal time before processing access units that may have missing RASL pictures. The decoder checks whether RASL pictures are present and pre-adjusts the removal time to prevent buffer overflow before it occurs, rather than reacting after the overflow happens.
Solution Approach 2:
The patent implements preliminary action by determining in advance whether RASL pictures are present in the bitstream and adjusting the CPB removal time accordingly before decoding subsequent access units. This allows the decoder to prepare the buffer timing in advance, ensuring correct operation whether or not RASL pictures are present.
2Reliability
If the video decoder adjusts CPB removal time for each CRA or BLA access unit, then correct decoding is maintained when RASL pictures are absent, but the complexity of buffering operations increases
Solution Approach 1:
The patent applies dynamics by making the CPB removal time adjustment conditional rather than fixed. The decoder dynamically determines whether adjustment is needed based on the presence or absence of RASL pictures, allowing the buffering operation to adapt its behavior to the actual bitstream conditions rather than following a rigid predetermined sequence.
Solution Approach 2:
The patent implements local quality by applying different buffering operations to different access units based on their specific characteristics. Instead of using a uniform approach for all access units, the decoder checks each CRA or BLA access unit individually and applies adjustment only where needed, tailoring the buffering operation to the local requirements of each access unit.
Data Source
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AI summary
In an example, the present disclosure provides for receiving in a video bitstream an access unit having a first random access point (RAP) picture and receiving in the video bitstream, after the access unit in the bitstream, a subsequent access unit having a second RAP picture. In a case that one or more random access skipped leading (RASL) pictures for the subsequent access unit are not present in the received video bitstream, shifting a picture buffer removal time earlier based on a picture buffer removal delay offset. Another example provides for receiving an access unit after an earlier initialization of the hypothetical reference decoder (HRD), the access unit having a RAP picture, wherein associated access units containing RASL pictures are not received and initializing a picture buffer removal time and a picture buffer removal delay offset in response to receiving the access unit and not receiving the associated access units containing RASL pictures.