Are my subtitle files uploaded to a server?

No. All parsing, editing and exporting happens in your browser with JavaScript. You can disconnect from the internet and the tool keeps working — that is the cheapest way to verify it.

Why do subtitle timings drift after trimming a video?

Because the subtitle file still refers to the original timeline. Cutting seconds or minutes off the start of a video shifts every cue by a fixed offset, so a single shift of that offset repairs the whole file.

Why do subtitles drift progressively instead of staying in sync?

That is a frame-rate mismatch: captions timed for 23.976 fps played on a 25 fps video drift a little more every minute. Fix it with a frame-rate retime instead of a shift.

Subtitle timeline studio — shift, sync & check SRT/VTT in your browser

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	#	Start	End	Dur	Text	CPL	CPS

Checks

Preset

Custom thresholds

CPL (chars/line) CPS (chars/sec) Min duration (ms) Max duration (ms) Max lines

Delivery check

Runs the rule set above over the whole file and applies the mechanical fixes: overlaps, gaps, minimum/maximum duration, line wrapping and splitting over-long cues. Anything that needs the words themselves to change (reading speed, text that simply does not fit) is reported, never rewritten. Undo works on the whole run.

Safe area preview

Frame Caption size (% of frame height)

Shows the cue you have selected (or the worst cue in the file) inside the frame, with the title-safe box and the areas short-form platform UI usually covers. Layout only — no video is loaded.

Timing

Shift (ms)

Stretch × Anchor (ms) this point stays put

Frame rate

→

For the gradual drift you get when captions were timed for one frame rate and the video plays at another. For a single fixed offset (trimmed intro, delayed audio) use Shift above.

Scope

All cues Selected only (0)

Pricing

Free

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Subtitle tools

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