refactor: replaced similar functions with improved generalized ones

[PlkMarudny]

What does this PR do?

Similar functions were replaced and consolidated.

Type of change

• Bug fix
• New feature (transition / preset / text anim / effect / API)
• Docs
• Refactor / internal

How was it verified?

• node --check server.js && node --check app.js && node --check mcp-server.js passes
• Opened the editor and confirmed the change in preview
• Confirmed the change in an export (fast or realtime), if it affects rendering
• Updated CLAUDE.md / README.md if the schema, props, or API changed

Checklist

• No new runtime dependencies added
• Preview and export render identically (single compositor)
• Commits are focused and messages are descriptive

Summary by CodeRabbit

• Improvements
  • Media imports now populate duration and dimensions more reliably.
  • Video thumbnails and audio waveforms are prepared consistently after import.
  • Audio channel isolation is handled consistently during playback and export.
  • Timeline gap closing and clip selection now behave more predictably.
  • Project and library media icons are displayed consistently.
  • Text sizing, measurement, and line spacing are more consistent across layouts.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 57330586-8c72-4c8c-bc83-e13f764f406b

📥 Commits

Reviewing files that changed from the base of the PR and between 8aac11f and 71f9b77.

📒 Files selected for processing (1)

• app.js

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📝 Walkthrough

Walkthrough

This update centralizes media metadata loading, icon selection, enabled-track filtering, channel-isolated audio routing, visible clip ordering, and text line-height calculation across app.js.

Changes

Shared application logic

Layer / File(s)	Summary
Media metadata and icon handling app.js	Media imports and library items use shared metadata loading, while bin and library rendering use shared media-kind icons.
Enabled-track gap utilities app.js	Gap operations obtain enabled tracks through a shared helper.
Channel-isolated audio routing app.js	Live playback, audio-hold refresh, and offline mixing reuse common splitter/merger routing.
Visible clip enumeration app.js	Frame drawing and hit testing use shared compositing-ordered visible clips.
Shared text line-height calculation app.js	Font fitting, measurement, and drawing use a common line-height helper.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• ronak-create/FableCut#17: Related changes to app.js audio channel separation and stereo mixing.

Suggested reviewers: ur5fot, xusnitdinov

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Title check	❓ Inconclusive	The title is related to the refactor, but it is too generic to convey the main change clearly.	Use a specific title that names the main refactor, such as consolidating media loading, audio routing, and clip selection helpers.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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