twineconvert

free · in-browser · no upload

VTT to ASS
Converter

Drop your WebVTT file. We'll convert it to ASS right here in your browser, your file never leaves your device.

or drop your file

Select your file here to get started

or drop your file here.

Accepts .vtt

nothing uploaded no file size cap no signup

How it works

Three steps. No upload, no signup.

  1. 1

    Drop your file

    Click the dropzone above or drag a WebVTT from your desktop. Files of any size, there's no upload, so there's no upload limit.

  2. 2

    Convert in your browser

    The conversion runs entirely in this tab using JavaScript and WebAssembly. Your file never touches our servers, we don't have any.

  3. 3

    Download

    Get your ASS the moment the conversion finishes. Convert another, or close the tab.

Files stay on your device

Your file is never uploaded. The entire conversion runs in your browser using WebAssembly. We can't see what you convert because we have no server to see it.

No file size limit

Server converters cap free users at 1-2 GB and gate larger files behind a paid plan. Since nothing uploads, our limit is whatever your browser can handle.

Free, no signup, no ads on conversions

No account required. No watermark on the output. No queue. Drop a file, get a converted file.

Why convert VTT → ASS

What this conversion is actually for

WebVTT is the browser-native subtitle format (`<track kind="subtitles">`); ASS is the format Aegisub and mpv prefer for advanced typesetting. Converting VTT to ASS lets you upgrade auto-generated YouTube captions (which export as VTT) into a stylable working file for proper typesetting.

A real example

You exported YouTube's auto-captions as `lecture.vtt`. You convert to `lecture.ass`, open in Aegisub, fix the speech-recognition errors line-by-line, and restyle the Default fontsize to match the slide aesthetic — much faster than retyping every line from scratch.

Troubleshooting

VTT positioning cues (line:80%, align:center) didn't carry over.

WebVTT positioning maps imperfectly to ASS positioning (which uses a different model: alignment 1-9 grid plus \pos overrides). We drop VTT positioning in this version and emit alignment 2 (bottom center). Re-add per-line positioning in Aegisub if it matters for your typesetting.

Formats involved

About WebVTT and ASS

WebVTT, Web Video Text Tracks

WebVTT is the W3C standard subtitle format for HTML5 video, used by every browser when you set `<track src="captions.vtt">` on a `<video>` element. Differs from SRT mainly in syntax (`.` decimal in timestamps, `WEBVTT` header, no cue numbers required) plus optional cue settings for position and style. YouTube, Vimeo, and modern OTT platforms all accept WebVTT.

How to open

Any text editor. Browsers render WebVTT inline when attached to a video element. Subtitle Edit and other tools convert between WebVTT and SRT.

Full WebVTT format guide →
ASS, Advanced SubStation Alpha

ASS (Advanced SubStation Alpha, sometimes spelled .ssa for its predecessor SubStation Alpha) is the styled-subtitle format used by Aegisub, fansubbed anime, and nearly every video player that supports advanced typesetting (VLC, MPV, mpv-style, IINA, PotPlayer). It's a section-based INI: `[Script Info]` for metadata, `[V4+ Styles]` for fonts/colors/positioning, `[Events]` for the actual `Dialogue:` lines. Captions can specify per-line styling, hard breaks (`\N`), inline override codes (`{\b1}bold{\b0}`, `{\i1}italic{\i0}`, `{\fnArial}font`), karaoke effects, and absolute screen positioning — none of which SRT or WebVTT express. Created in 2003; libass is the de-facto rendering engine across mpv, ffmpeg, and most modern players.

How to open

Aegisub is the canonical editor (free, all platforms). VLC, MPV, IINA, and PotPlayer render ASS overlays natively. ffmpeg can burn ASS into a video track or pass through as a soft subtitle stream. Any text editor opens .ass as plain UTF-8.

Full ASS format guide →

Related tools

Convert other files to ASS

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FAQ

Common questions

Is this VTT → ASS converter really free?

Yes. No signup, no watermark, no daily file count limit. Every conversion runs in your browser, your file never touches our servers because there are no servers.

Where does my file go when I convert it?

Nowhere. The conversion runs entirely in your browser using JavaScript and WebAssembly. Your file is never uploaded to our servers. We don't have any servers handling files, there's nothing for us to log, store, or accidentally leak.

What's the maximum file size?

Whatever your browser can hold in memory. Practically, this means a few hundred MB on most computers, significantly larger than the 1-2 GB caps that server-upload converters charge for. Very large files (multi-GB) may require closing other browser tabs first.

Why convert WebVTT to ASS?

HTML5 video captions and accessibility tracks. Styled subtitles for video — anime fansubs, professional video typesetting, karaoke timings. The most common reason to convert is compatibility, ASS works in places where WebVTT doesn't, or vice versa.

How do I open a WebVTT file in the first place?

Any text editor. Browsers render WebVTT inline when attached to a video element. Subtitle Edit and other tools convert between WebVTT and SRT.

Does this work offline?

Once the page is loaded, the conversion itself runs entirely offline. The first time you use a tool, your browser downloads the conversion library (a one-time cache). If you reload while offline, the page won't load, but you can install the site as a Progressive Web App for full offline use.

Can I convert multiple files at once?

Single file at a time for now. Batch conversion is on the roadmap, for now, drop one file, download the result, then convert the next.