AnyTool
Your files never leave your device. All processing happens locally in your browser.

How do I edit subtitles synced to a video without uploading it?

Open AnyTool's Subtitle Editor, load a video plus an SRT or VTT file (or start fresh), and edit each cue's text and timings while a live caption overlay shows them on the playing video. You can shift or scale all timings at once, then export SRT/VTT — or optionally burn the captions into the video with libass. The edit/export path is instant and runs entirely in your browser, with no upload, no CDN and no watermark.

  • Load a video + SRT/VTT, or start fresh
  • Edit cue text and timings with a live caption overlay
  • Shift or scale all timings at once
  • Export SRT/VTT or burn-in (libass) — instant, client-side

What is

Subtitle editing

Subtitle editing adjusts the text and timing of caption cues so they stay in sync with the video. A synced editor shows a live caption overlay during playback and can bulk-shift or scale all cue times, then export to SRT/VTT or burn the captions permanently into the picture (e.g. via libass). Client-side editing runs in the browser, so the video and subtitles are never uploaded.

Video Tools

Related terms

SRTVTTcaption syncburn-inlibass

How to Edit Subtitles Synced to a Video

Edit and sync caption cues against playback in your browser.

3 minWeb browser
  1. 1

    Load video + subtitles

    Drop in a video and an SRT/VTT file, or start fresh — they stay on your device.

  2. 2

    Edit and sync

    Adjust cue text and timings with a live overlay, and shift or scale all timings as needed.

  3. 3

    Export

    Save SRT/VTT instantly, or optionally burn the captions into the video — nothing is uploaded.

Result: Edited subtitles (SRT/VTT) or a captioned video

Frequently Asked Questions

Yes — a live caption overlay shows each cue on the playing video as you edit text and timings.

You can load an existing SRT/VTT or start fresh, then fine-tune every cue against playback.

Shift or scale all timings at once to nudge or stretch every cue together.

That fixes a constant offset (shift) or a drifting/speed mismatch (scale) across the whole file.

Export SRT/VTT instantly, or optionally burn the captions into the video with libass — and nothing is uploaded.

The edit and export path is instant and fully client-side; the video and subtitles stay in your browser.

Detailed Explanation

Methodology

How the Subtitle Editor Works

AnyTool edits subtitles entirely on the main thread — no ffmpeg is needed for the editing itself. It parses SRT or VTT into cues and syncs them to a native HTMLVideoElement by listening to the timeupdate event, drawing the active cue in a styled caption overlay so you preview exactly what plays. Timing fixes are plain math: shift every cue by an offset or scale timings to fix drift. Edited SRT/VTT is exported instantly as a blob. An optional burn step renders the captions into the picture using the self-hosted ffmpeg libass subtitles filter (no CDN) with a bundled font. Single-threaded ffmpeg is deliberate: the multi-threaded core needs SharedArrayBuffer + cross-origin isolation (COOP/COEP), which would block cross-origin ad iframes.

  • Runs client-side — the video and captions are never uploaded
  • Pure main-thread editing — no ffmpeg for the edit itself
  • Parses SRT/VTT; syncs cues to HTMLVideoElement via timeupdate
  • Styled caption overlay preview; shift / scale timings as plain math
  • Instant SRT/VTT export
  • Optional burn via self-hosted ffmpeg libass subtitles filter + bundled font (no CDN)
Privacy & Security

Privacy vs Upload-based Editors

Many online subtitle editors upload your video and caption file to a server and cap the free tier or require an account. AnyTool edits locally in the browser, so neither the video nor the captions leave your device, there is no size limit and no signup, and it works offline after the first load.

Subtitle editing: AnyTool vs typical tools
CapabilityAnyToolTypical tools
Data handlingIn your browserOften uploaded
Live sync previewYes (timeupdate overlay)Varies
Timing fixesShift + scale (drift)Often shift only
ExportInstant SRT / VTTVaries
Optional burn-inSelf-hosted libass (no CDN)Server-side
CostFree, no signupFree/limited

AnyTool is a privacy-first client-side subtitle editor — editing runs locally and nothing is uploaded.