SubStamper / Free Online SRT Subtitle Timing Tool

Create SRT subtitles online in seconds. SubStamper is a free, open-source subtitle timing tool that runs entirely in your browser. Upload audio, paste lyrics or dialogue, tap spacebar to sync each line, and download a standard .srt file. No server, no signup, no installation — works offline.

For the best experience, use a desktop browser. Post-editing is not available on mobile.

Drop an MP3 here or click to browse

3
Hold Space = mark start  |  Release = mark end & next line Tap & hold = mark start  |  Release = mark end & next line
Space hold = mark start  |  release = mark end & advance Tap & hold = mark start  |  release = mark end & advance
00:00:00,000 00:00:00,000
Re-timing line — hold Space to mark start, release to mark end. Press Esc to cancel.

Click any row to re-time that line (audio seeks 5s before its start).

#StartEndLyrics
00:00:00,000 00:00:00,000

Frequently Asked Questions

What is SubStamper?

SubStamper is a free, open-source browser-based SRT subtitle timing tool. Upload audio, paste your lyrics or dialogue, hold the spacebar to mark start and end times for each line, then download a standard .srt subtitle file. No server, no signup, no installation needed. It works completely offline once loaded.

How do I create SRT subtitles?

Open SubStamper and drag an MP3 (or any audio file) onto the drop zone. Paste your subtitle text, one line per subtitle. Click "Start Timing" and hold the spacebar when each line begins — release when it ends. The tool advances to the next line automatically. Once all lines are timed, review your timestamps and click "Download .srt" to save.

Is SubStamper really free?

Yes, 100% free and open source under the MIT license. No hidden costs, no premium tier, no account required, no usage limits. The source code is available on GitHub.

Does it work offline?

Yes. Once the page loads, SubStamper works without any internet connection. Your audio and text are processed entirely in your browser using the Web Audio API — nothing is ever sent to a server.

What audio formats are supported?

SubStamper accepts any format your browser supports: MP3, WAV, OGG, FLAC, M4A, AAC, and more. Just drag and drop or click to browse.

Can I re-time a single line without starting over?

Yes. In the preview screen, click any row to re-time just that line. The audio seeks 5 seconds before the line's start time so you can restamp it precisely.

What makes SubStamper different from other subtitle tools?

SubStamper is designed for one task: timing subtitles quickly. No bloated timeline editors, no account walls, no AI that guesses your timestamps wrong. It's three files (HTML, CSS, JS) with zero dependencies. Hold spacebar, release, done. It's the fastest way to create an SRT file from scratch.

Features

Common Uses

The Fastest Way to Create SRT Subtitles

Most subtitle tools make you drag boxes on a timeline or type timestamps by hand. SubStamper takes a different approach: you listen to the audio and hold the spacebar while each line is spoken or sung. That's it. The SRT subtitle generator handles formatting, numbering, and timestamp precision automatically.

Whether you need a lyrics subtitle creator for a music video or a quick way to sync subtitles with audio for a podcast, SubStamper gets the job done in a single pass. Made a mistake? Click any line in the preview to re-time it — the audio seeks back automatically so you can fix one line without redoing the rest.

Everything runs client-side. Your files stay on your machine. There's no upload, no processing queue, no watermark. Just a fast, focused subtitle timing tool that works exactly when you need it.