Free online SMI to VTT converter

Some media players, browsers, and video-hosting workflows require WebVTT captions instead of SAMI subtitles. Converting an .smi file preserves its timed dialogue in a format designed for HTML5 video, browser playback, and modern caption editors.

What the SMI format is

SMI, usually referring to SAMI (Synchronized Accessible Media Interchange), is an HTML-like subtitle format originally developed by Microsoft. It stores caption text inside markup such as <SYNC Start="5000">, where the Start value is a timestamp in milliseconds from the beginning of the video.

SAMI files can contain CSS styling, speaker labels, positioning information, and several language tracks identified by class attributes. They are commonly found with older Windows media, educational video, DVD-ripping, and Korean media releases. Older versions of Windows Media Player and subtitle tools often created or used .smi files.

Because SMI is an HTML-based format rather than a simple cue list, opening it in a web browser may show markup instead of rendering captions. The file may also use a legacy character encoding, such as Windows-1252, EUC-KR, or another regional encoding.

What the VTT format is

WebVTT, normally saved with a .vtt extension, is the caption format supported by the HTML5 <track> element and many browser-based video players. A valid file begins with WEBVTT and stores each cue with a start and end timestamp:

WEBVTT

00:00:05.000 --> 00:00:08.500
Caption text appears here.

VTT uses periods before milliseconds and requires three-digit millisecond fields. SMI commonly uses integer millisecond values, so a converter must calculate each cue's end time from the next synchronization point. VTT also supports cue settings for positioning, alignment, and line placement, although not every SMI style has a direct VTT equivalent.

Choose VTT when captions will be loaded by an HTML5 player, embedded in a website, edited in a modern subtitle application, or processed by a service that does not accept SAMI.

How to convert SMI to VTT

Using the built-in online converter

1. Open the SMI-to-VTT converter on 101convert.com; it can be used for free without installing software.
2. Upload the .smi file.
3. If the file contains multiple language tracks, select the required language or caption class when the converter provides that option.
4. Start the conversion and download the resulting .vtt file.
5. Open the downloaded file in a text editor and verify that it begins with WEBVTT, contains timestamps in HH:MM:SS.mmm form, and has no missing dialogue.

Using Subtitle Edit on a desktop

Subtitle Edit can import SAMI subtitles and export WebVTT on supported versions.

1. Open Subtitle Edit and choose File → Open, then select the .smi file.
2. If prompted for an encoding, choose the encoding that displays the original characters correctly. Do not continue with garbled text; re-open the file using another encoding.
3. Check the language track, cue timing, line breaks, and any overlapping subtitles in the subtitle grid.
4. Choose File → Save as or the format-selection command, select WebVTT or .vtt, and save the file.
5. Test the VTT with the same video, because conversion cannot repair incorrect source timings or missing language selection.

Converting a batch of files

For repeated conversion, use a subtitle application that supports command-line or batch processing and explicitly lists both SAMI input and WebVTT output. Generic media commands such as ffmpeg are not a dependable SAMI parser: support for SAMI varies by build, and HTML markup or language classes may be interpreted incorrectly. A subtitle-specific converter is safer for batches.

Quality and compatibility limits

• End times may be inferred. SMI commonly records only each cue's start time. Converters usually end a cue when the next SYNC begins, so the final cue may receive a guessed duration or remain open until the video ends.
• Language selection matters. One SMI file can contain several language variants. Exporting the wrong class produces a valid VTT with the wrong captions, while exporting all classes may create duplicate or overlapping cues.
• Formatting may change. Basic italics, line breaks, and some color information can survive, but SMI CSS, absolute positioning, font declarations, speaker styling, and proprietary tags may be discarded or approximated.
• Encoding errors require correction before export. If names or non-Latin characters appear corrupted in the SMI editor, changing the VTT extension will not fix them. Reopen the source with the correct character encoding and then export.
• Validate the result. Check for a WEBVTT header, increasing cue times, valid arrows written as -->, blank lines between cues, and timestamps with three millisecond digits. Also test playback in the target browser or media player.