Add your TTML file
Drop one or more .ttml files onto the converter above, or browse for them. They load into browser memory only — nothing is uploaded, so there is no size-based pricing and no server queue.
TTML to SMI
Converting a .ttml file to .smi extracts the document's content from its office package into a portable form. Free, private, and validated — the file never leaves your browser.
Private for supported formats — processed in your browser
Runs on your deviceConvert supported files
Drop TTML files here
Batch files can each use a different output. Nothing uploads for local conversions.
Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.About converting Timed Text Markup Language to SAMI captions
Converting a .ttml file to .smi extracts the document's content from its office package into a portable form. A .ttml file is a Timed Text Markup Language document: an XML vocabulary in which each <p> element carries begin and end (or dur) attributes plus the caption text. It is the W3C standard that broadcast and streaming systems use as their interchange format for captions and subtitles.
An .smi file is a SAMI caption document: HTML-like markup in which <SYNC Start=…> elements mark the millisecond at which a caption appears, and the caption runs until the next SYNC. Microsoft designed it as an accessibility format, so a single file can carry several languages selected by CSS class. For this route the practical draw is several language tracks in one file, chosen by class and plain text and editable anywhere — balanced against never formally standardised, so real-world files vary in structure, which is worth knowing before you commit a large batch.
Why convert TTML to SMI?
The practical trigger for this conversion is usually a mismatch: with .ttml, far more verbose than SubRip or WebVTT for the same cues. Switching to .smi buys you several language tracks in one file, chosen by class, which is why it is the better fit for captioning legacy Windows Media and Silverlight content. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
TTML vs SMI at a glance
| Aspect | Timed Text Markup Language (.ttml) | SAMI captions (.smi) |
|---|---|---|
| Format type | Text-based — characters and structure, so there is no visual quality loss | Text-based — characters and structure, so there is no visual quality loss |
| How it stores data | the root <tt> element declares the TTML namespace and optional ttp: parameters such as frameRate, tickRate, and timeBase | the document has an HTML shape: <SAMI> wrapping <HEAD> with a <STYLE> block and <BODY> with the SYNC elements |
| Strongest at | delivering captions to broadcast and streaming platforms that mandate a TTML profile | captioning legacy Windows Media and Silverlight content |
| Weak spot | far more verbose than SubRip or WebVTT for the same cues | never formally standardised, so real-world files vary in structure |
| Metadata | styling, layout, and region definitions are read past rather than applied: timing and text convert, presentation does not, and no external resource is ever fetched | style-class and title information describes presentation and language selection, not the cues; conversion keeps timing and text |
Pick SMI as the output
Select .smi in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if SMI is selectable, the route is real and validated.
Convert on your device
Press Convert. The package is unzipped in memory and its XML content parsed locally; nothing is uploaded.
Verify and download
Each result is signature-checked before the download unlocks, so a failed encode can never masquerade as a valid SMI file. Outputs keep the original filename with the .smi extension.
TTML to SMI questions, answered
Will converting TTML to SMI lose quality?
There is no visual quality to lose — ttml is text-oriented and smi is text-oriented, so the question is structural fidelity. Text, ordering, and basic structure are preserved; complex layout, embedded objects, and styling beyond the target's model are simplified.
Is it private to convert TTML files here?
Yes — the .ttml file is processed inside your browser tab and never uploaded. The package is unzipped in memory and its XML content parsed locally; nothing is uploaded. Close the tab and the file is gone from memory.
Where will the SMI file work?
Windows Media Player, VLC, PotPlayer, and MPC-HC read .smi, and Subtitle Edit converts it. Browsers do not. Novus Convert parses the SYNC blocks locally with document types and external entities refused and script and style content removed before any text is read, then writes any of the twelve timed-text targets.
Will the SMI file be bigger or smaller than my TTML?
It depends on the content: the document has an HTML shape: <SAMI> wrapping <HEAD> with a <STYLE> block and <BODY> with the SYNC elements. Convert one representative file first and compare before batch-processing a large set.
What happens to the metadata in my TTML file?
In .ttml, styling, layout, and region definitions are read past rather than applied: timing and text convert, presentation does not, and no external resource is ever fetched. Re-encoding through the browser pipeline does not carry embedded metadata into the output, which doubles as a privacy scrub — check the exported file if you specifically need tags preserved.
Can I convert SMI back to TTML?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .ttml → .smi → .ttml is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.