Motion-Constrained AV1 Encoding for Tile-Based Streaming
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Solution Overview
Problem
Current AV1 video codecs lack a method to limit loop filters on tile boundaries, which is necessary for efficient encoding and decoding of ultra-high definition images in tile-based streaming, particularly for 360 VR and panorama images, as they do not have the option to disable loop filters on tile boundaries like HEVC codecs do.
Innovation Solution
A motion-constrained AV1 encoding method that limits the motion prediction range and sets specific parameters to disable loop filters on tile boundaries, ensuring that motion vectors do not cross tile boundaries and synchronizing frame header parameters to enable decoding of segmented images using a single standard AV1 decoder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If loop filters are applied on tile boundaries in AV1 encoding, then encoding quality is improved, but decoding complexity increases and tile-based streaming efficiency deteriorates
Solution Approach 1:
The image is divided into multiple independent tiles that can be encoded and decoded separately. By disabling loop filters on tile boundaries, each tile becomes self-contained with no cross-tile filtering operations, enabling parallel processing and reducing decoding complexity while maintaining encoding quality within each tile.
Solution Approach 2:
Loop filters are selectively disabled only on tile boundary blocks while remaining enabled on non-boundary blocks. This local differentiation maintains high encoding quality within tile interiors while eliminating the complexity of cross-tile filtering operations, achieving a balance between quality and decoding efficiency.
2Measurement precision
If motion prediction search range is not limited in AV1 encoding, then motion prediction accuracy is improved, but encoding time increases significantly
Solution Approach 1:
The motion prediction search range is pre-limited to exclude blocks on tile boundaries before the actual motion estimation process begins. This preliminary constraint prevents unnecessary search operations across tile boundaries, significantly reducing encoding time while maintaining sufficient motion prediction accuracy for typical video content.
Solution Approach 2:
The motion prediction search range parameter is modified to impose constraints on block positions relative to tile boundaries. By changing the search space parameters to exclude boundary regions, the encoding process achieves faster processing speeds while preserving motion prediction accuracy for blocks within valid regions.
3Adaptability or versatility
If frame header parameters are not synchronized across tiles, then encoding flexibility is improved, but decoding reliability deteriorates
Solution Approach 1:
Frame header parameters are synchronized across all tiles to create a universal header structure that can be reliably processed by standard decoders. This universal approach ensures that segmented tiles can be independently decoded and then stitched together, maintaining decoding reliability while still allowing tile-based parallel processing flexibility.
Solution Approach 2:
While frame headers are synchronized for reliability, tile-specific parameters can still be differentiated locally. This allows each tile to have customized encoding parameters where needed while maintaining the synchronized frame header structure that ensures reliable decoding and proper tile integration.
4Manufacturing precision
If ultra-high definition images are streamed as complete frames, then image quality is maintained, but network bandwidth requirements increase
Solution Approach 1:
Ultra-high definition images are divided into multiple smaller tile segments that can be streamed independently. This segmentation reduces the data transmission volume for each stream, allowing selective transmission of only those tiles currently in the user's field of view, thereby reducing overall network bandwidth requirements while maintaining full image quality when all tiles are assembled.
Solution Approach 2:
The tile-based streaming system dynamically selects which tiles to transmit based on real-time user viewing position and field of view. This dynamic adaptation allows the system to maintain high image quality for visible regions while minimizing data transmission for regions outside the current view, significantly reducing overall bandwidth consumption compared to transmitting complete frames.
Data Source
AI summary
There is provided a motion-constrained AV1 encoding method and apparatus for tile-based streaming of an ultra-high definition image, which encodes an image such that the image can be decoded by integrating tile-based segmented images at a bit stream level without modifying an AV1 standard decoder. According to an embodiment of the present disclosure, the motion-constrained encoding method includes: limiting a motion prediction range based on a format and a size of an image; and predicting motion vectors regarding tiles constituting the image, based on the limited motion prediction range. Accordingly, a tile-based streaming service is possible through motion-constrained AV1 encoding of an ultra-high definition image (360 VR image or panorama image). In addition, a consumer electronic device is enabled to integrate and decode segmented images by using a single standard AV1 decoder.