Add your DFXP file
Drop one or more .dfxp 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.
DFXP to SMI
Converting a .dfxp 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 DFXP 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 DFXP timed text to SAMI captions
Converting a .dfxp file to .smi extracts the document's content from its office package into a portable form. A .dfxp file is a TTML document written to the Distribution Format Exchange Profile — the profile the W3C defined for handing finished captions to a distributor. The extension signals the profile; the contents are ordinary TTML, which is why the same parser reads both.
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 DFXP to SMI?
The practical trigger for this conversion is usually a mismatch: with .dfxp, the distinct extension implies a distinct format and regularly confuses tooling. 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.
DFXP vs SMI at a glance
| Aspect | DFXP timed text (.dfxp) | 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 document is TTML: a <tt> root, a <body>/<div> structure, and <p> cues with begin and end attributes | the document has an HTML shape: <SAMI> wrapping <HEAD> with a <STYLE> block and <BODY> with the SYNC elements |
| Strongest at | delivering captions to a platform whose spec names DFXP by extension | captioning legacy Windows Media and Silverlight content |
| Weak spot | the distinct extension implies a distinct format and regularly confuses tooling | never formally standardised, so real-world files vary in structure |
| Metadata | profile and parameter attributes are read for timing purposes only; styling and layout are not carried into caption targets that cannot express them | 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.
DFXP to SMI questions, answered
Will converting DFXP to SMI lose quality?
There is no visual quality to lose — dfxp 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 DFXP files here?
Yes — the .dfxp 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 DFXP?
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 DFXP file?
In .dfxp, profile and parameter attributes are read for timing purposes only; styling and layout are not carried into caption targets that cannot express them. 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 DFXP?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .dfxp → .smi → .dfxp is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.