SMI to TTML Subtitle Converter
Transform Synchronized Accessible Media Interchange subtitles into TTML format instantly and privately in your browser.
Drag & drop your SMI file here
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Supports .smi, .sami, .html files up to 50 MB
Free Online SMI to TTML Converter
Our SMI to TTML converter reads Synchronized Accessible Media Interchange input and produces Timed Text Markup Language output entirely in your browser. Source SMI timing (whole milliseconds (Start=...)) is converted to TTML begin and end timing (seconds, such as 1.500s). SMI styling and markup are stripped, leaving basic ready-to-use output. The conversion runs client-side, so your subtitle files are never uploaded to a server.
SMI to TTML Code Syntax & Structure Inspection
Side-by-side code inspection illustrating header definitions, timestamp syntax, and cue payload formatting
SMI vs TTML Technical Specifications
SMI
SMI (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.
TTML
TTML (Timed Text Markup Language) is a W3C XML subtitle format. TTML stores captions in <p> elements with begin and end timing expressed as seconds or clock values, and the broader format family supports rich styling, regions, and profiles such as IMSC and ITT.
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
Streaming Delivery
Produce basic TTML subtitles, then add any profile-specific metadata or validation required by your platform.
Professional Interchange
Use TTML as the rich, validatable interchange format for professional timed-text pipelines.
IMSC / ITT Profiles
Start with plain TTML timing and text when preparing files for an IMSC or ITT workflow.
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.
How It Works
- 1
Upload your .smi file by dragging it in or browsing.
- 2
The parser reads the Synchronized Accessible Media Interchange structure and extracts each cue's start, end, and text.
- 3
Source SMI timing (whole milliseconds (Start=...)) is converted to TTML begin and end expressions in seconds.
- 4
SMI styling and markup are stripped, and cues are formatted as TTML <p> elements.
- 5
The output .ttml file is generated and ready to download.
More Subtitle Tools
Frequently Asked Questions
It reads a Synchronized Accessible Media Interchange file, parses each cue's timing and text, strips SMI markup, and writes a basic .ttml file. Source SMI timing (whole milliseconds (Start=...)) is converted to TTML begin and end timing in seconds.
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. The output is plain timed TTML text without SMI styling or delivery-profile metadata.
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 TTML timing (seconds (1.500s) or clock values).
Yes. The converter is fully responsive and works in any modern mobile browser on iOS and Android.
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