SMI to STL Subtitle Converter
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100% local processing in your browser. No upload. No waiting.
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Supports .smi, .sami, .html files up to 50 MB
More Subtitle Tools
How It Works
Upload SMI File
Drag & drop or select your .smi file
Convert Instantly
We process it locally in your browser
Download STL
Get your .stl file immediately
Why Choose AllSubConverter?
Your Privacy Matters
Everything runs in your browser. Your files are never uploaded.
Lightning Fast
Optimized processing engine converts files in seconds.
Free & Local
Each file can be up to 50 MB. Batches can contain up to 200 files or 1 GB total.
Works Everywhere
Works on Windows, Mac, Linux, iOS, Android - any modern browser.
Free Online SMI to STL Converter
Our SMI to STL converter reads Synchronized Accessible Media Interchange input and produces Spruce Subtitle output entirely in your browser. Source SMI timing (whole milliseconds (Start=...)) is converted to STL timing (SMPTE HH:MM:SS:FF frame timecodes at 29.97 fps). SMI styling and markup are stripped, leaving valid, ready-to-use output. The conversion runs client-side, so your subtitle files are never uploaded to a server.
Input Format
SMISMI (SAMI, Synchronized Accessible Media Interchange) is a Microsoft subtitle format built from HTML-like <SYNC> elements whose Start attribute is given in milliseconds. SMI supports multiple language tracks through CSS classes and was widely used for Windows Media Player captions and accessibility content.
Output Format
STLSTL (Spruce Subtitle) is a text-based subtitle format used in DVD authoring and some broadcast workflows. Entries use comma-separated start and end timecodes followed by subtitle text, with the pipe character (|) for line breaks. The output is accepted by DVD authoring tools and Spruce-based workflows.
Features
Why Convert?
Format Differences
Common Use Cases
DVD Authoring
Produce STL subtitle files for DVD authoring tools that expect the Spruce format.
Broadcast Workflows
Generate STL for Spruce-based and legacy broadcast subtitle pipelines.
Frame-Accurate Timing
Output SMPTE frame-based timecodes, quantized to 29.97 fps STL timing.
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.
SCC (Scenarist Closed Captioning)
The North American broadcast alternative: convert to SCC for CEA-608 caption delivery.
Frequently Asked Questions
It reads a Synchronized Accessible Media Interchange file, parses each cue's timing and text, strips SMI markup, and writes a valid .stl file. Source SMI timing (whole milliseconds (Start=...)) is converted to STL timing (SMPTE HH:MM:SS:FF frame timecodes at 29.97 fps).
Absolutely. Every conversion runs client-side in your browser. No subtitle data, file contents, or metadata is ever transmitted to a server.
SMI styling and markup are dropped. Timing is quantized to 29.97 fps STL frames, so sub-frame precision from the source is not retained.
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 SMI timing (whole milliseconds (Start=...)) is converted to STL timing (SMPTE HH:MM:SS:FF frame timecodes).
Yes. The converter is fully responsive and works in any modern mobile browser on iOS and Android.