Audit Subtitle Sync Drift Across Video Timestamps — Free
Captions that drift out of sync by even 500 milliseconds render media inaccessible for deaf and hard-of-hearing viewers. Manual offset adjustment without tracking drift rates leads to constant re-adjustments throughout a video.
The proof surface
Free path: the tool computes locally in this browser with no key and no account. Where an AI step helps, any free chat assistant works — free tiers exist (Google AI Studio, Groq), but plans and limits change, so check the provider's own page. No third-party service is claimed here as verified: UNCONFIRMED — model has no browsing access this session.
Why the flat version breaks
Subtitle files often exhibit progressive timing drift due to frame rate mismatches (e.g., 23.976 fps vs 24 fps). Mapping drift points across timestamps allows content creators and accessibility editors to compute exact linear correction factors.
How to use the subtitled sync drift docket in four passes
Pause the video at 5-10 minute intervals and measure how early or late the caption text appears relative to audio.
Record positive milliseconds if captions arrive late, or negative if they appear before the spoken audio.
The docket calculates progressive drift per minute and identifies if the issue is a constant delay or a frame-rate stretch.
Use the recommended global stretch factor in your subtitle tool to resync the entire video in one operation.
SAMPLE DATA, NOT A VERIFIED CLAIM: starter record audits a 45-minute documentary with progressive caption drift up to 1.4 seconds. Replace these values with your own source before you rely on anything.
What breaks first
Adjusting individual captions manually without checking drift rate
Fixing single captions manually takes hours and fails when progressive drift shifts every subsequent subtitle line.
Ignoring frame-rate conversion differences
Mixing 23.976 fps captions with 25 fps video causes a continuous 1-second drift every 41 seconds.
What you pay otherwise
| The usual route | What it leaves out | Cost |
|---|---|---|
| Commercial caption auto-sync SaaS | Per-minute transcription and alignment fees | $2–$5 per video minute |
| Manual editor time | Hours of tedious manual subtitle tweaking | 2–3 hours per hour of video |
| This page + the free subtitled sync drift docket | Computed in your tab, result on screen before you type anything | $0 |
Try the free subtitled sync drift docket right here
Load starter record and adjust millisecond offsets to see calculated drift rate update.
FIRST-LOAD · sample record filed
Take it into the free subtitled sync drift docket
The companion app runs the same logic with a numbered intake, three starter records, a stateful share link, the one-time printable layer, and the local history shelf.
Open the free subtitled sync drift docket →Keep the work if you will use it again
Full subtitle sync drift calculation and frame-rate adjustment factor.
The on-screen result is free and complete. The one-time layer adds a tangible file you keep.
Boundary: Calculates linear timing adjustments based on user inputs. Does not edit media or subtitle files directly.