SMI to VTT Subtitle Converter
Transform SAMI subtitle files into WebVTT format for modern web video players and platforms.
Drag & drop your SMI file here
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Supports .smi, .sami, .html files up to 50 MB
Free Online SMI to VTT Converter
Our SMI to VTT converter takes Microsoft SAMI subtitle files and produces W3C-compliant WebVTT for web video. SAMI uses HTML-like SYNC elements with millisecond timing offsets and CSS styling, while VTT uses the WEBVTT header with HH:MM:SS.mmm timestamps. This tool parses the SAMI HTML structure, strips all markup, extracts subtitle text, converts timing to VTT format, and adds the mandatory WEBVTT header. The result works in HTML5 video, YouTube, and JavaScript video players.
SMI to VTT Code Syntax & Structure Inspection
Side-by-side code inspection illustrating header definitions, timestamp syntax, and cue payload formatting
SMI vs VTT Technical Specifications
SMI
SMI (SAMI, Synchronized Accessible Media Interchange) is a subtitle format developed by Microsoft for Windows Media Player. SAMI files use an HTML-like structure where each subtitle entry is enclosed in SYNC elements, with a Start attribute giving the display time in milliseconds. The format supports CSS styling, multiple language tracks via CLASS attributes, and metadata in the document head. SAMI is still found on Korean video platforms, older media archives, and educational content.
VTT
VTT (WebVTT) is the W3C standard subtitle format for web video. A VTT file starts with the literal header WEBVTT on the first line, followed by cue blocks using HH:MM:SS.mmm --> HH:MM:SS.mmm timestamps (period before milliseconds). VTT supports optional cue settings (positioning, alignment, sizing), inline styling tags, NOTE comments, and CSS blocks.
Format Differences
Conversion Troubleshooting & Gotchas
Practical solutions for player compatibility, character encoding, and timing synchronization
Subtitle timing drifts or appears out of sync on media players
Video files frequently differ in framerate (e.g., 23.976 fps vs 25 fps). If the timing drifts steadily, use our Subtitle Sync tool to adjust the global offset or framerate stretch.
Characters appear as garbled symbols or question marks (Mojibake)
Legacy files saved in Windows-1252, Shift-JIS, or GBK may render incorrectly. Our exporter standardizes output to clean UTF-8. Use our Subtitle Encoding Converter if the source file is corrupted.
Overlapping captions when multiple speakers talk simultaneously
Different formats handle overlapping dialogue differently. If your target player cannot render stacked cues cleanly, open the file in our Subtitle Editor to adjust individual cue timings.
Video editing software (Premiere, DaVinci, Final Cut) rejects the file
Professional NLE software enforces strict syntax rules. Our converter eliminates malformed line breaks and non-standard tags, producing clean, standardized files.
Features
Why Convert?
Common Use Cases
Korean Platform to Web
Convert SMI subtitles from Korean video platforms into VTT for HTML5 video embedding on websites targeting international audiences.
YouTube Caption Upload
Transform SAMI subtitles into VTT files that YouTube Studio accepts for caption uploads.
E-Learning Subtitles
Convert SAMI subtitles from older educational content into VTT for e-learning platforms that accept WebVTT.
JavaScript Player Integration
Load SAMI-originated subtitles as VTT in Video.js, Plyr, or JW Player for web-based video streaming.
Legacy Content Web Migration
Move old Windows Media Player SAMI subtitles to modern web video by converting to VTT.
Multi-Platform Distribution
Produce VTT (for web) alongside SRT (for devices) from SAMI source files for broad compatibility.
Related Formats
SMI (SAMI)
The input format: HTML-based Microsoft subtitle format with SYNC elements.
SRT (SubRip)
The universal alternative: if your target is smart TVs or desktop players, convert SMI to SRT.
SCC (Scenarist Closed Captioning)
The broadcast alternative: for caption delivery to television platforms.
How It Works
- 1
Upload your .smi file by dragging it into the converter or browsing.
- 2
The parser reads the HTML structure and identifies each SYNC element.
- 3
Subtitle text is extracted, with all HTML markup stripped.
- 4
Millisecond Start values are converted to VTT HH:MM:SS.mmm timestamp format.
- 5
The WEBVTT header is prepended, producing a valid .vtt file for web video.
More Subtitle Tools
Frequently Asked Questions
VTT is the standard choice for HTML5 track elements and is widely supported by web video platforms and JavaScript players. Use SRT for smart TVs and desktop media players.
SAMI stores timing as millisecond offsets in Start attributes. The converter transforms these into VTT HH:MM:SS.mmm format. End times come from the next SYNC element; the final cue receives a three-second fallback duration.
Yes, it is free with no registration or watermarks. Each file can be up to 50 MB.
Yes. The converter always adds WEBVTT as the first line of the output.
SAMI CSS styling is removed. VTT supports its own styling mechanisms (inline tags, CSS blocks), but the converter outputs plain text cues. Add VTT styling manually if needed.
Yes. The converter is fully responsive.
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