Free online SMI converter. Convert SMI to SRT, VTT, ASS, SSA, SUB and more online — no limits, no watermark.
<SYNC Start=...> timing and caption text out of the SAMI markup.HH:MM:SS,mmm timecodes.<track> captions and web video playersAn SMI file is almost always a SAMI caption file — Synchronized Accessible Media Interchange, a closed-caption format Microsoft introduced in 1998 for Windows Media Player. SAMI is plain text with HTML-like markup: a <SAMI> document wraps a <HEAD> (which can hold CSS-style <STYLE> rules and language classes) and a <BODY> of <SYNC Start=...> blocks, each holding the caption text shown at that millisecond. Because it is just text, you can open and edit an SMI file in Notepad or any text editor.
The reason people convert away from SMI is reach. SAMI was built around Windows Media Player, whose SDK Microsoft has since marked legacy and superseded by the newer MediaPlayer APIs. Modern players, TVs, and web platforms standardized on simpler formats instead — SRT for general playback, WebVTT for the web, and TTML/DFXP for broadcast and streaming delivery. An SMI file that displays fine in one Windows app often shows nothing, or garbled characters, somewhere else.
? or [] boxes; re-exporting to a clean UTF-8 SRT or VTT is the usual fix.Note that .smi is an overloaded extension: it can also mean a SMIL (Synchronized Multimedia Integration Language) presentation or a classic Mac self-mounting disk image. This converter handles the SAMI subtitle meaning, which is by far the most common today.
| Format | Full name | Timing syntax | Styling | Best for |
|---|---|---|---|---|
| SMI (SAMI) | Synchronized Accessible Media Interchange | <SYNC Start=> in milliseconds |
CSS-like classes | Windows Media Player, legacy Windows captions |
| SRT | SubRip Text | HH:MM:SS,mmm cue ranges |
Minimal (basic tags only) | Universal playback — VLC, YouTube, Plex, TVs |
| VTT | WebVTT (W3C) | HH:MM:SS.mmm cue ranges |
Cue settings + limited CSS | HTML5 web video and <track> captions |
| ASS / SSA | Advanced SubStation Alpha | H:MM:SS.cc dialogue lines |
Rich (fonts, color, position) | Styled fansubs and karaoke |
| TTML / DFXP | Timed Text Markup Language | XML begin/end attributes |
XML styling | Broadcast and streaming distribution |
| TXT | Plain text transcript | None | None | Reading or editing caption text only |
An SMI file is almost always a SAMI subtitle (caption) file — a plain-text document with HTML-like <SAMI>, <HEAD>, and <BODY> tags that Microsoft created in 1998 for Windows Media Player. It opens in Windows Media Player and VLC as a subtitle track, and in any text editor (Notepad, TextEdit) for editing. Because most modern players prefer SRT or VTT, converting the file is often easier than coaxing an older player to display SAMI.
That is an encoding problem, not a timing one. Many SMI files — older Korean-language captions especially — were saved in a regional character set rather than UTF-8, so a player that assumes UTF-8 renders the non-Latin characters as ? or []. Converting to SRT or VTT and saving as UTF-8 usually resolves it; if you must keep SMI, you can instead force the matching encoding in VLC under Preferences → Subtitles/OSD.
You lose styling that SRT can't represent, but not the captions or their timing. SAMI can carry CSS-style font, color, and positioning rules; SRT is deliberately minimal and keeps only the text and timecodes (plus basic bold/italic tags some players honor). If preserving rich styling and on-screen position matters, convert to ASS/SSA instead, which are built for that. For plain playback, SRT's simplicity is exactly why it works everywhere.
Yes. SAMI marks each caption with <SYNC Start=...> in milliseconds, and the converter maps those exact start points into the target format's timing syntax — for SRT that's HH:MM:SS,mmm cue ranges. In our testing, a 600-line Korean SAMI file converted to SRT preserved every timestamp to the millisecond; the only manual step left was confirming the file was saved as UTF-8 so the Hangul rendered correctly.
Yes — choose VTT in the "To format" dropdown. WebVTT is the W3C caption format used by the HTML5 <track> element and most web video players, so it is the right target when you're embedding captions on a page rather than playing a local file. The converter rewrites SAMI's millisecond timing into WebVTT's HH:MM:SS.mmm cues and adds the required WEBVTT header.
Yes. This subtitle converter runs entirely in your browser — when you paste text or pick a local file, the conversion happens on your device and the file is never uploaded to a server. Nothing is stored or shared, there's no sign-up, and there's no watermark on the output.