chore(backend): update to v176ca82 with HLS window preloading support

[mkdir700]

Summary

Update backend submodule to v176ca82, introducing HLS window preloading functionality for improved video playback experience.

New Features

🚀 HLS Window Preloading with Configurable Strategy

• Automatic Background Preloading: Automatically preload previous N windows in the background when accessing HLS files
• Configurable Preload Count: Add preload_previous_windows configuration option (default: 1, min: 0)
• Non-blocking Execution: Preload tasks run in background using asyncio.create_task without blocking user requests
• Smart Cache Detection: Skip already-cached windows to optimize resource usage and avoid redundant transcoding
• Priority Management: Low priority (3) for preload tasks to avoid impacting active user requests
• Performance Metrics: Returns (queued_count, cached_count) metrics for monitoring and debugging

Technical Changes

API Layer (src/app/api/)

• deps.py: Add get_preload_strategy dependency injection provider
• v1/jit.py: Auto-trigger preload on window access with asyncio.create_task for non-blocking execution

Configuration (src/app/config/)

• manager.py: Add preload_previous_windows setting (default: 1, min: 0 to disable)
• schemas.py: Add preload_previous_windows field to TranscodeConfig schema

Service Layer (src/app/services/)

• preload_strategy.py: Implement preload_previous_windows method with:
  • Cache key validation to avoid redundant transcoding operations
  • Window ID calculation for determining previous windows
  • Low-priority task queuing for background processing
  • Comprehensive error handling and logging for debugging
  • Metrics tracking (queued_count, cached_count)

Benefits

• ✅ Improved User Experience: Proactively loads likely-needed segments for smoother playback and reduced buffering
• ✅ Performance Optimization: Maintains performance for active requests through priority management
• ✅ Resource Efficiency: Smart cache detection prevents unnecessary transcoding and reduces resource usage
• ✅ Flexibility: Configurable preload count allows tuning based on use case (set to 0 to disable)
• ✅ Monitoring: Built-in metrics for tracking preload effectiveness and cache hit rates

Testing

• Verify automatic preload triggers on window access
• Confirm non-blocking behavior doesn't affect user requests
• Test cache detection skips already-cached windows
• Validate configurable preload count (0, 1, 2+)
• Check metrics reporting accuracy

Related Commits

• Backend: 176ca82 - feat(jit): implement HLS window preloading with configurable strategy (基于 AI 生成音标，并用颜色标记连读、重音 #8)

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • 更新后端子模块指针至最新提交，保持代码基线同步。
  • 无用户可见的功能变化、界面改动或性能影响，无需任何操作。

[coderabbitai]

Walkthrough

将后端子模块指针从 d747012bbd0a394f644939e9c15212ea769274ab 更新为 176ca823ac2e6365f0721e43725c633b2d5aa9da；未发现其他变更，未修改导出/公共声明与控制流。

Changes

Cohort / File(s)	Change Summary
子模块指针更新 backend	更新子模块引用提交：d747012b → 176ca823；无其他文件变更

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

我在仓库草丛蹦一蹦，
指针挪一步，提交号轻轻换个风。
没有函数惊醒梦，
没有流程起波澜涌。
只留胡萝卜一根——为平静的小变动🥕

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	标题简洁地反映了后端子模块更新及 HLS 窗口预加载支持，明确总结了 PR 的核心改动。
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch mkdir700/update-backend

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📥 Commits

Reviewing files that changed from the base of the PR and between 394b93d and 648aa01.

📒 Files selected for processing (1)

• backend (1 hunks)

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• GitHub Check: test (ubuntu-latest, 20)
• GitHub Check: test (macos-latest, 20)
• GitHub Check: test (windows-latest, 20)

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