Two-Stage CABAC Parser for Tile-Based HEVC Transcoding
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Solution Overview
Problem
The challenge in video transcoding lies in efficiently converting a tile-based HEVC video sequence into a non-tile based AVC or MPEG-2 video sequence, due to differences in processing orders and context models required for entropy coding, which complicates the conversion process.
Innovation Solution
A two-stage context adaptive binary arithmetic coding (CABAC) parser is employed to parse the HEVC video bitstream in both tile scan and raster scan orders, allowing for the efficient transcoding of tile-based HEVC videos into non-tile based formats by storing and applying CABAC state data across CTUs, thereby addressing the parsing order and context memory requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a tile-based HEVC video sequence is decoded using conventional methods, then the video can be decoded according to HEVC standard, but the transcoding process becomes complex and inefficient when converting to non-tile based formats like AVC or MPEG-2
Solution Approach 1:
The patent segments the parsing process into two distinct stages: a first stage that parses video frames in tile scan order to generate auxiliary data, and a second stage that parses in raster scan order using the auxiliary data. This segmentation allows each stage to handle specific aspects of the parsing complexity, thereby improving overall transcoding efficiency while managing device complexity through structured division of the parsing task.
Solution Approach 2:
The first stage parsing performed in tile scan order serves as a preliminary action that generates auxiliary data containing CABAC state information. This preliminary parsing prepares the necessary context data before the second stage raster scan parsing begins, enabling more efficient entropy decoding in the target format without requiring complete re-parsing of all video data.
2Productivity
If CABAC state data is stored and applied across CTUs to enable raster scan parsing, then transcoding efficiency improves, but memory requirements increase
Solution Approach 1:
The patent extracts only the necessary CABAC state information from the tile-based parsing process and stores it as auxiliary data for use in raster scan order parsing. By extracting only the essential context data rather than storing complete parsing states, the system achieves improved compression throughput while minimizing the memory resources required to support the two-stage parsing approach.
3Extent of automation
If tile scan order parsing is used for HEVC decoding, then parallel processing is enabled, but the entropy coding context model differs from non-tile based formats causing transcoding complications
Solution Approach 1:
The auxiliary data generated in the first stage acts as an intermediary that bridges the tile scan order parsing (which enables parallel processing) and the raster scan order parsing (which provides format compatibility with AVC and MPEG-2). This intermediary data structure allows the system to maintain the benefits of parallel processing while achieving compatibility with non-tile based formats through the second stage parsing.
Data Source
AI summary
A two-stage context adaptive binary arithmetic coding (CABAC) parser is provided to efficiently transcode an input video bitstream that is partitioned into tiles into a non-tiled based video bitstream. A picture of the input video bitstream is partitioned into one or more tiles, each of which has multiple coding tree units (CTUs) according to the HEVC standard. The two-stage CABAC parser parses the input video bitstream in tile scan order in the first stage and generates a list of identified CTUs, whose CABAC state data are saved for the second stage parsing. In the second stage parsing, the two-stage parser parses the same input video bitstream in raster scan order using the saved CABAC state data of the identified CTUs.