feat: implement soft threshold for video fragmentation

[gkozlenko]

Add a 10% tolerance (0.9 threshold) when cutting video fragments to prevent excessive chunk durations. Previously, the splitter strictly waited for a keyframe after exceeding the target duration, often causing significant overshoots.

By allowing cuts slightly before the target duration is reached, resulting chunk sizes align much closer to the requested target. Audio-only streams remain unaffected (1.0 threshold) and are cut strictly at the target due to their high sample granularity.

[gemini-code-assist]

Summary of Changes

Hello @gkozlenko, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant improvement to video fragmentation by implementing a soft threshold mechanism. This change allows for more precise control over video chunk durations, mitigating the problem of fragments exceeding their target length due to strict keyframe alignment. The modification ensures better adherence to desired fragment sizes for video while maintaining strict adherence for audio, leading to more predictable and efficient media processing.

Highlights

• Soft Threshold for Video Fragmentation: Implemented a 10% tolerance (0.9 threshold) for cutting video fragments, allowing cuts slightly before the target duration to prevent excessive chunk lengths.
• Audio Fragmentation Unchanged: Audio-only streams retain a strict 1.0 threshold, ensuring they are cut precisely at the target duration due to their high sample granularity.
• Improved Chunk Duration Alignment: The new approach ensures that resulting video chunk sizes align much closer to the requested target duration, addressing previous issues of significant overshoots.
• New Test Coverage: Added a new comprehensive test file for FragmentListBuilder to validate the new fragmentation logic for both video and audio tracks.

Changelog

• lib/fragment-list-builder.js
  • Added VIDEO_DURATION_THRESHOLD and AUDIO_DURATION_THRESHOLD constants to control fragmentation tolerance.
  • Modified fragment duration calculation to apply a track-specific threshold, allowing video fragments to be cut slightly earlier.
• test/fragment-list-builder.js
  • Added a new test file to thoroughly test the FragmentListBuilder class.
  • Included test cases for scenarios with no tracks, no samples, and correct splitting for both audio/video and audio-only tracks, verifying the new threshold logic.
• test/tests.js
  • Included the new fragment-list-builder test file in the main test suite.

Activity

• No human activity has been recorded on this pull request yet.

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[github-actions]

Test Coverage Summary Statistics

• Lines: 94.96%
• Statements: 94.98%
• Functions: 93.35%
• Branches: 79.14%

[gemini-code-assist]

Code Review

This pull request introduces a soft threshold for video fragmentation, which is a nice improvement to get chunk durations closer to the target. The implementation is straightforward and the logic is sound. New constants are introduced for thresholds, which is good practice. I appreciate the addition of comprehensive tests for the new functionality, which cover both video and audio-only scenarios. I have one minor suggestion to improve the test code by reducing duplication.