Open to Closed GOP Conversion for Video Editing
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Solution Overview
Problem
Existing video compression methods, such as H.264, face challenges when Open GOP bitstreams are cut, leading to broken references and the need for extensive decoding and re-encoding, which is computationally intensive and degrades video quality, especially during video editing and consolidation processes.
Innovation Solution
A method to convert Open GOP to Closed GOP by decoding and re-encoding specific frames, re-referencing B frames only to the I frame, and flagging the I frame as an IDR frame, minimizing the need for further decoding and re-encoding of subsequent GOPs, thus maintaining image quality and reducing processing load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Open GOP interframe compression is used to achieve greater video compression, then compression efficiency is improved, but reference integrity is worsened when bitstreams are cut
Solution Approach 1:
The patent segments the video stream into distinct GOP structures with clear boundaries. By converting Open GOPs to Closed GOPs, each GOP becomes a self-contained unit that can be independently processed and cut without affecting reference integrity. The B frames are re-encoded to reference only within their own GOP, creating natural segmentation points.
Solution Approach 2:
The patent performs preliminary conversion of Open GOPs to Closed GOPs before editing or consolidation operations. By pre-re-encoding B frames to reference only within their GOP and flagging I frames as IDR frames, the system prepares the bitstream in advance to prevent reference breaking during subsequent cutting operations.
2Reliability
If extensive decoding and re-encoding is performed to fix broken references, then reference integrity is improved, but computational load is worsened
Solution Approach 1:
The patent applies partial action by performing decode-re-encode operations only on specific frames (B frames) that need re-referencing, rather than processing the entire video stream. The I frames and subsequent frames can be copied directly without re-encoding, reducing the overall computational burden while still achieving reference integrity.
3Reliability
If extensive decoding and re-encoding is performed to fix broken references, then reference integrity is improved, but video quality is worsened due to multiple compression cycles
Solution Approach 1:
The patent minimizes quality degradation by performing decode-re-encode operations only on the necessary B frames rather than the entire GOP. The I frame and subsequent frames are copied directly from the original stream, avoiding multiple compression cycles and preserving their original quality.
Solution Approach 2:
The patent changes the reference parameters of B frames during re-encoding, directing them to reference only within their own GOP structure. This parameter change enables reference integrity without requiring full stream re-encoding, thus maintaining video quality while fixing the reference breaking issue.
4Productivity
If Open GOP structure is used to enable broader frame references, then compression ratio is improved, but editing flexibility is worsened when consolidating clips
Solution Approach 1:
The patent segments the video into Closed GOP structures where each GOP is self-contained. This segmentation allows editing operations to work with independent units, improving flexibility during consolidation and clipping while maintaining the compression benefits of interframe prediction within each GOP.
Solution Approach 2:
The patent changes the GOP structure parameter from Open to Closed by re-encoding B frames with modified reference pointers. This parameter change enables both good compression ratios and editing flexibility, as the Closed GOP structure allows arbitrary cutting points while maintaining reference integrity within each GOP boundary.
Data Source
AI summary
Methods of converting an open group of pictures (GOP) to a Closed GOP are described that remove backward references to the GOP prior to the GOP undergoing conversion in an Open GOP interframe-encoded video stream. Within the GOP undergoing conversion, bipredictive frames with backward references to the prior GOP are replaced with frames referring only to the I frame of the GOP undergoing conversion, which is flagged as an IDR frame. Consolidation and assembly of video clips that are encoded using Open GOP compression schemes generally result in broken interframe references between GOPs. To address this, existing methods involve significant decoding and re-encoding of edited video sequences. The described methods serve to break the backward chain of references in the encoded stream, resulting in reduced re-encoding requirements, with attendant reduced quality degradation of the edited sequence.