Convert WebVTT (.vtt) to Advanced SubStation Alpha

WebVTT (.vtt) is built for browser captioning: a WEBVTT header, then cues as a HH:MM:SS.mmm --> HH:MM:SS.mmm timecode range with a line or two of text, optionally with cue settings or <v Speaker> voice tags. Advanced SubStation Alpha (.ass), the format Aegisub, many fansub groups, and advanced players like MPV and VLC use, is structured very differently: a [Script Info] header, a [V4+ Styles] section defining fonts, colors, outlines, and screen position, and an [Events] section referencing those styles per line.

SubToolDesk's VTT to ASS converter parses your WebVTT cues locally in your browser, discards the WEBVTT header and any voice tags, converts every timecode to ASS's centisecond H:MM:SS.cc format, and writes out a complete, valid .ass file with a working [Script Info] block, a single Default style, and one Dialogue: line per cue.

How to convert VTT to ASS (step-by-step)

• Drag your .vtt file onto the converter above, or click “Upload File” to browse for it.
• Confirm the auto-detected format badge reads VTT.
• Toggle Strip speaker labels on if your source has <v Speaker> tags or leading name labels you don't want carried over.
• Press Download to save a valid .ass file, named to match your original file.

What the generated .ass file contains

The output is a complete, player-ready ASS file. It includes a real [Script Info] block, a [V4+ Styles] section with one style named Default (white text, a thin outline and shadow for legibility over video, bottom-centered), and an [Events] section with a Dialogue: line for every cue. You can open the result in Aegisub afterward to adjust fonts, colors, or position.

What happens to WebVTT-only features

WebVTT's cue settings (like align:start position:10%) and <v Speaker Name> voice tags don't have a direct ASS equivalent in this converter's output; cue settings are dropped and voice tags are removed by the Strip speaker labels toggle, same as every other converter on this site. If you need that same information in ASS, it's expressed differently there, through per-line MarginL/MarginR/MarginV overrides or a dedicated style, and is a manual follow-up step once you have the base file.

Why timecodes look different in ASS

WebVTT times to the millisecond with a period separator (00:00:09.400); ASS times to the centisecond, one-hundredth of a second, with a non-zero-padded hour (0:00:09.40). The converter handles that rounding automatically, so a cue starting at 9.4 seconds in the source lands at the correct centisecond in the output.

Why people move from VTT to ASS

• Fansubbing and anime release groups, where ASS's styling and positioning overrides are the de facto standard, even when the source caption was exported as WebVTT.
• Editors working in Aegisub, which expects ASS as its native project format rather than a plain VTT import.
• Players and pipelines that render styled overrides, like MPV or certain streaming encoders, where WebVTT's cue settings don't map to the same positioning and font control ASS offers.
• Starting a styled subtitle project from a web-exported caption track, using this converter to get a structurally valid ASS file in place before adding styles by hand.

Privacy by architecture, not by policy

Parsing the VTT and writing the ASS file both happen in JavaScript running in your browser tab. There is no upload endpoint this feature could hit, which matters whether the source is a public YouTube caption export or a confidential recording.

What this tool intentionally doesn't do

It writes one Default style and doesn't attempt to guess at karaoke timing, per-character colors, or positioning overrides, those are a manual (or Aegisub-assisted) step once you have a valid base file. It also doesn't translate WebVTT cue settings into ASS margin or alignment overrides automatically; that mapping isn't one-to-one and is left for you to apply deliberately if you need it.