[aniruddhaadak80]

What Problem This Solves

In standalone one-file HTML mode (--one-file), slide transitions flicker with a brief blank frame. This happens because videos are embedded as base64 data URIs in data-background-video attributes, and the browser must re-decode the massive base64 string on each transition.

Root Cause

The existing fixBase64VideoBackground function recombines split base64 sources but does not prevent the decode delay. Each time RevealJS creates a new <video> element for a slide, the browser parses and decodes the inline base64 data, which takes hundreds of milliseconds for large videos.

What Changed

• Added preCreateBlobUrls() function that runs at RevealJS ready time
• Converts all data-URI video sources to Blob URLs via fetch() + URL.createObjectURL()
• Subsequent slide transitions use the cached Blob objects in memory instead of re-decoding base64

How Tested

• 77/77 convert tests pass
• Template renders without Jinja2 errors
• No Python API changes — purely client-side JS in the template

Behavior Trade-offs

• Slight increase in memory usage (Blob URLs are held in memory)
• One-time conversion cost at page load (negligible for typical presentations)
• Backward compatible: only activates in one_file mode with data URIs

Fixes #426

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.10%. Comparing base (1d90682) to head (0fc66d4).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #678   +/-   ##
=======================================
  Coverage   79.10%   79.10%           
=======================================
  Files          23       23           
  Lines        2178     2178           
=======================================
  Hits         1723     1723           
  Misses        455      455           

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[aniruddhaadak80]

Diagnosis of the two red checks on this head (0fc66d4), neither is caused by this diff (which only touches revealjs/firebase templates): - markdown-link-check: 2 archive.org links in paper/paper.md returned 503 at check time (run 33259629185). External/archive-side flake, file untouched by this PR - safe to rerun/ignore. - pre-commit.ci ty hook: failed downloading networkx from files.pythonhosted.org (DNS temporary failure in name resolution). Transient infra, ruff/codespell/all else passed. Retriggering the checks should clear it.

[aniruddhaadak80]

Closing as superseded by upstream #693 (fd3f178) — verified my earlier fix is a strict subset. Details in my comment above.

[jeertmans]

#693 has little to do with HTML conversion, since it's about the Qt presenter, so I don't see why it's related.

[aniruddhaadak80]

You are right, and I owe you a correction: #693 touches manim_slides/present/player.py (the Qt presenter) while my PR touched the revealjs/firebase HTML templates - zero file overlap, so my superseded claim was wrong. I misread a same-symptom fix (visual flicker) as a same-layer fix. Sorry for the noise. The template-side data-URI to Blob pre-conversion may still be a valid improvement on its own - would you like me to reopen this for proper review, or prefer I leave it closed?