Video Transcoding Using CTS and DTS Frame Analysis
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Solution Overview
Problem
Traditional MP4 encoding processes cannot overlap transcoding, compression, or optimization with streaming and playback, limiting the inclusion of bidirectionally coded frames and failing to optimize transcoded media based on source encoding information.
Innovation Solution
The method determines frame types in a video sequence using composition time stamps (CTS) and decoding time stamps (DTS), calculates frame type ratios, and allocates bits to each frame type to enable efficient transcoding and encoding of target video frames, allowing for the inclusion of B-frames and B-REF frames, which improves video quality and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional two-step MP4 encoding process is used, then encoding simplicity is maintained, but transcoding cannot overlap with streaming and playback
Solution Approach 1:
The patent segments the encoding process into distinct phases: a first encoding pass that generates frames and writes them to an mdat box, and a second pass that writes metadata to a moov box. This segmentation allows transcoding operations to occur during the first pass while streaming and playback can proceed with the generated stream, enabling overlap between transcoding and playback operations.
2Productivity
If frame size prediction is used in traditional transcoding, then transcoding speed is improved, but bidirectionally coded B-frames cannot be included
Solution Approach 1:
The patent implements feedback by analyzing the actual frame ordering and types from the source video stream during the encoding process. The encoder uses this feedback information to make informed decisions about target frame types, allowing accurate inclusion of B-frames and B-REF frames while maintaining transcoding speed through efficient frame type determination based on source frame analysis.
3Productivity
If source encoding information is not applied, then encoding independence is maintained, but optimization of transcoded media is reduced
Solution Approach 1:
The patent performs preliminary analysis of the source video stream to determine source frame types and ordering before generating the target stream. This preliminary action includes identifying I-frames, P-frames, and B-frames in the source sequence, which informs subsequent encoding decisions. By preparing this information in advance, the encoder can optimize the transcoded media more effectively without significantly increasing overall process complexity.
Data Source
AI summary
Systems and methods of transcoding video sequences for delivery in a mobile network. A source video sequence including source video frames is received and a source video frame type associated with each of the source video frames is determined based on a differential between a composition time stamp (CTS) and a decoding time stamp (DTS) associated with each of the source video frames. A frame type ratio value for the target frame-types is calculated based on a longest mini-GOP length. A target frame size of each target video frame is determined based on the frame type ratio value and a target transcoding rate, and each of the target video frames in a target video track is encoded to the target frame size to form a target video sequence.