STL to SMI Subtitle Converter
Transform Spruce Subtitle text into SMI privately in your browser.
Drag & drop your STL file here
or click to browse
Supports .stl files up to 50 MB
Free Online STL to SMI Converter
Our STL to SMI converter reads Spruce Subtitle text input and produces a single-language Synchronized Accessible Media Interchange document entirely in your browser. Source STL timing is converted to SMI millisecond Start attributes. Bracketed inline tags are removed, pipe separators become newlines, HTML special characters are escaped, and blank SYNC elements mark cue ends. The conversion runs client-side, so your subtitle files are never uploaded to a server.
STL to SMI Code Syntax & Structure Inspection
Side-by-side code inspection illustrating header definitions, timestamp syntax, and cue payload formatting
STL vs SMI Technical Specifications
STL
STL (Spruce Subtitle) is a text-based subtitle format used in DVD authoring and some broadcast workflows. Each entry uses comma-separated start and end timecodes followed by the subtitle text, with the pipe character (|) denoting line breaks. This text STL variant is distinct from the binary EBU STL broadcast format.
SMI
SMI (SAMI, Synchronized Accessible Media Interchange) is a Microsoft subtitle format using HTML-like <SYNC> elements with Start times in milliseconds. SMI supports multiple language tracks through CSS classes and is suitable for Windows Media Player and legacy accessibility workflows.
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
Windows Media Captions
Produce SMI captions for Windows Media Player and Microsoft-based playback environments.
Accessibility
Deliver SAMI accessibility captions for legacy corporate and educational media systems.
Multi-Language Files
Create a single-language SMI track that you can extend in SAMI-aware tooling if multiple classes are required.
Related Formats
SRT (SubRip)
The universal plain-text alternative: convert to SRT for maximum device compatibility.
VTT (WebVTT)
The web alternative: convert to VTT if your target is HTML5 video or YouTube.
TTML (Timed Text Markup Language)
The structured XML alternative: convert to TTML when a basic timed-text document is more suitable.
How It Works
- 1
Upload your .stl file by dragging it in or browsing.
- 2
The parser reads the Spruce Subtitle structure and extracts each cue's start, end, and text.
- 3
Source STL timing (SMPTE HH:MM:SS:FF frame timecodes) is converted to SMI timing (whole milliseconds (Start=...)).
- 4
Bracketed inline tags are removed, HTML special characters are escaped, and line breaks become <br> tags.
- 5
The output .smi file is generated and ready to download.
More Subtitle Tools
Frequently Asked Questions
It reads a Spruce Subtitle text file, parses each cue's timing and text, and writes a single-language SAMI document with an ENCC class, timed SYNC elements, escaped HTML text, and blank end markers. Source STL timing is converted to SMI milliseconds.
Absolutely. Every conversion runs client-side in your browser. No subtitle data, file contents, or metadata is ever transmitted to a server.
Yes. Bracketed STL tags are removed, pipe separators become <br> line breaks, and HTML special characters are escaped. Timing is converted to SMI milliseconds.
Yes, completely free with no sign-up, no watermarks, and files up to 50 MB each. All processing happens in your browser, so your files are never uploaded to a server.
Source STL timing (SMPTE HH:MM:SS:FF frame timecodes) is converted to SMI timing (whole milliseconds (Start=...)).
Yes. The responsive page works in modern mobile browsers.
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