Free, instant, and entirely in your browser — your subtitle file is never uploaded.
MicroDVD counts frames, not seconds — this has to match the video.
ASS is a typesetting language that happens to carry subtitles. Named styles, exact positioning, rotation, fades, karaoke timing and vector drawing all live in the file, split across a [Script Info], a styles and an [Events] section.
WebVTT is SRT rebuilt for the web: the same cue structure, a WEBVTT header line, a dot instead of a comma before the milliseconds, and optional positioning settings after the timestamp. It is the only subtitle format HTML5 video natively understands.
This conversion catches people out more than any other into VTT, because the web feels modern and an ASS file is full of capability — so it seems as though it should survive. It does not. A browser's caption track has no styles, no positioning worth the name and no drawing, so a typeset release arrives on your site as ordinary lines at the bottom of the frame. If the typesetting mattered, the honest answer is to burn it into the video rather than convert it; if only the dialogue mattered, this is exactly right.
You want WebVTT because the subtitle has to work in a browser. An HTML5 <track> element reads VTT and nothing else, and HLS and DASH streams expect it too. If you are putting a video on your own site, or feeding a web player, this is the conversion that makes captions appear at all.
This is a downgrade in capability, and worth doing on purpose. The source format is a typesetting language: named styles, exact positions, fades, karaoke timing, even vector drawings. The target has none of that — it has text and two timestamps. So the words and the timing come across intact, and everything that decided how they looked on screen is dropped. Signs translated in place, on-screen labels positioned over the original, coloured speaker attribution: all of it becomes ordinary subtitle lines. That is the trade for a file almost every player and platform will accept without argument.
No. The conversion runs in your browser using JavaScript — your ASS file is read from disk, converted in memory and handed back as a download. Nothing is transmitted, so there is nothing for us to store or delete. You can disconnect from the internet after this page loads and the conversion still works.
This conversion catches people out more than any other into VTT, because the web feels modern and an ASS file is full of capability — so it seems as though it should survive. It does not. A browser's caption track has no styles, no positioning worth the name and no drawing, so a typeset release arrives on your site as ordinary lines at the bottom of the frame. If the typesetting mattered, the honest answer is to burn it into the video rather than convert it; if only the dialogue mattered, this is exactly right.
The page checks before it converts. Subtitle formats are identified by what is inside the file rather than by the extension — which matters, because .sub alone is used by three unrelated formats. If you hand this page something that is not ASS, it says so and points you at the all-format converter instead of producing a broken file.