Add your SMI file
Drop one or more .smi 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.
SMI to SUB
Converting a .smi file to .sub 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 SMI 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 SAMI captions to MicroDVD subtitles
Converting a .smi file to .sub extracts the document's content from its office package into a portable form. 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.
A .sub file in the MicroDVD convention is a frame-based subtitle list: every line reads {startFrame}{endFrame}text, with a pipe character separating the lines inside one cue. Because the timing is expressed in frames rather than milliseconds, a MicroDVD file only means anything alongside the frame rate of the video it was timed to. For this route the practical draw is extremely compact — one line per cue and frame timing matches the source video exactly when the frame rate is known — balanced against meaningless without the correct frame rate; the wrong value drifts the whole file, which is worth knowing before you commit a large batch.
Why convert SMI to SUB?
The practical trigger for this conversion is usually a mismatch: with .smi, never formally standardised, so real-world files vary in structure. Switching to .sub buys you extremely compact — one line per cue, which is why it is the better fit for playing back subtitles that were timed against a specific video rip. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
SMI vs SUB at a glance
| Aspect | SAMI captions (.smi) | MicroDVD subtitles (.sub) |
|---|---|---|
| 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 has an HTML shape: <SAMI> wrapping <HEAD> with a <STYLE> block and <BODY> with the SYNC elements | each cue is one line: {startFrame}{endFrame} followed by the text, with | separating multiple display lines |
| Strongest at | captioning legacy Windows Media and Silverlight content | playing back subtitles that were timed against a specific video rip |
| Weak spot | never formally standardised, so real-world files vary in structure | meaningless without the correct frame rate; the wrong value drifts the whole file |
| Metadata | style-class and title information describes presentation and language selection, not the cues; conversion keeps timing and text | there is no metadata section; the only header-like content is the frame-rate declaration, which is read on input and written on output |
Pick SUB as the output
Select .sub in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if SUB 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 SUB file. Outputs keep the original filename with the .sub extension.
SMI to SUB questions, answered
Will converting SMI to SUB lose quality?
There is no visual quality to lose — smi is text-oriented and sub 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 SMI files here?
Yes — the .smi 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 SUB file work?
VLC, MPC-HC, and most desktop players read MicroDVD .sub, and Subtitle Edit converts it. Browsers do not. Novus Convert reads the frame rate from the file's own {1}{1} declaration and falls back to 23.976 when none is present; a binary VobSub .sub is rejected with an explanation rather than being parsed as text. MicroDVD output is written at 25 fps with that rate declared in the first line, so a converted file round-trips to the frame.
Will the SUB file be bigger or smaller than my SMI?
It depends on the content: each cue is one line: {startFrame}{endFrame} followed by the text, with | separating multiple display lines. Convert one representative file first and compare before batch-processing a large set.
What happens to the metadata in my SMI file?
In .smi, style-class and title information describes presentation and language selection, not the cues; conversion keeps timing and text. 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 SUB back to SMI?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .smi → .sub → .smi is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.