Fix filmstrip 404s by matching sitespeed.io's actual filmstrip cadence#166
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The previous filmstrip fix assumed sitespeed.io writes one JPG per VisualProgress change point and built URLs from those timestamps. That assumption is wrong: VisualProgress is sampled at video-frame cadence (every ~33 ms) while the filmstrip plugin writes files on a fixed 100 ms grid. Most change points fall between filmstrip frames and therefore 404 — including FirstVisualChange itself when it lands on a 100 ms boundary like 700 ms. Construct the timestamps directly from FVC/LVC using sitespeed.io's actual rule — ms 0, plus FVC when not on a 100 ms boundary, plus every 100 ms multiple strictly inside (FVC, LVC), plus LVC when not on a 100 ms boundary. Verified against the Sweden run on wikimedia.sitespeed.io: every constructed URL hits a real file. VisualProgress is still consulted to tag each frame with its rendered-% for the divergence-colour accent on the column view. Co-authored-by: Claude Opus 4.7 (1M context) noreply@anthropic.com
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The previous filmstrip fix assumed sitespeed.io writes one JPG per
VisualProgress change point and built URLs from those timestamps.
That assumption is wrong: VisualProgress is sampled at video-frame
cadence (every ~33 ms) while the filmstrip plugin writes files on
a fixed 100 ms grid. Most change points fall between filmstrip
frames and therefore 404 — including FirstVisualChange itself when
it lands on a 100 ms boundary like 700 ms.
Construct the timestamps directly from FVC/LVC using sitespeed.io's
actual rule — ms 0, plus FVC when not on a 100 ms boundary, plus
every 100 ms multiple strictly inside (FVC, LVC), plus LVC when not
on a 100 ms boundary. Verified against the Sweden run on
wikimedia.sitespeed.io: every constructed URL hits a real file.
VisualProgress is still consulted to tag each frame with its
rendered-% for the divergence-colour accent on the column view.
Co-authored-by: Claude Opus 4.7 (1M context) noreply@anthropic.com