Is the SRT to SMI conversion free?

Yes, completely free with no sign-up, no watermarks, and files up to 50 MB each. All processing happens locally in your browser, so your subtitle files are never uploaded to any server.

Can I convert SRT to SMI on mobile?

Yes. The converter works in any modern mobile browser on iOS and Android. Open the page, upload your SRT file, and download the converted SMI directly to your device.

What happens to subtitle text formatting during conversion?

Cue line breaks are maintained as markup. Required characters such as &, are escaped so the SAMI remains valid. You can edit the resulting file manually to add intentional HTML-like formatting.

Does the converter support styled or positioned SRT cues?

SRT itself does not support positioning or styling natively. This converter focuses on timing and text. HTML-like tags sometimes used in non-standard SRT are escaped and appear as literal text rather than live SMI formatting.

Are the millisecond timestamps accurate?

Yes. Each SRT timestamp is converted to a precise millisecond offset. For example, 00:01:30,500 becomes Start=90500 in the SYNC element. End times are handled the same way, so cue duration is preserved exactly.

What does a SYNC element look like in the output?

A cue start looks like: Subtitle text here . At the cue end time, the converter writes a blank ENCC paragraph. The generated SYNC elements do not include closing tags.

Can I edit the SMI file after conversion?

Yes. Since SMI is an HTML document, you can open it in any text editor and modify the CSS, add language tracks, adjust timing, or edit text. The structure is human-readable and editable.

Is my subtitle data private?

All conversion happens client-side in your browser. No subtitle data is uploaded to a server, and the downloaded file remains on your device.

What if my SRT file has encoding issues?

The converter handles UTF-8 encoded SRT files (the modern standard). If your file uses a legacy encoding like EUC-KR or Shift-JIS, convert it to UTF-8 first using a text editor before uploading.

How large can my SRT file be?

Each file can be up to 50 MB. The converter processes files entirely in your browser. Large feature-length subtitle files may take longer, depending on your device and browser.

Does the converter handle SRT files with overlapping timestamps?

The original start and end millisecond values are preserved. Each cue is converted independently, but overlapping cues can interact differently in players that honor the blank end SYNC, so review overlapping scripts before delivery.

Can I batch convert multiple SRT files to SMI?

Yes. Drop several SRT files on this page and they open together in the workspace Batch tool with the SMI format pre-selected, converting every file at once. For converting whole folders at scale, use the Batch Converter page.

What file extension should the output have?

The output file uses the .smi extension, which is the standard for SAMI subtitle files. This extension is recognized by Windows Media Player, Korean streaming platforms, and subtitle editing tools that support SMI.

SRT to SMI Subtitle Converter

Convert SubRip subtitles to SAMI format for players and workflows that still request SMI captions.

Drag & drop your SRT file here

or click to browse

Supports .srt files up to 50 MB

Core Engine Architecture

About SRT to SMI

This converter transforms SubRip (SRT) subtitle files into SAMI (Synchronized Accessible Media Interchange) format. SMI is an HTML-like captioning format originally developed by Microsoft that wraps subtitle cues inside SYNC elements with millisecond timing. While SRT remains the common interchange format, SMI is still encountered in Korean media workflows, legacy Windows Media deployments, and archival video systems that expect HTML-structured captions rather than plain-text subtitles.

Payload & Syntax Inspector

SRT to SMI Code Syntax & Structure Inspection

Side-by-side code inspection illustrating header definitions, timestamp syntax, and cue payload formatting

Millisecond Sync

input.srt

SRT SOURCE

1
00:00:01,000 --> 00:00:04,000
Hello, world!
 
2
00:00:04,500 --> 00:00:08,000
This is a subtitle file.
 
3
00:00:08,500 --> 00:00:12,000
Converted locally!

output.smi

SMI RESULT

<SAMI>
<BODY>
<SYNC Start=1000><P Class=ENCC>Hello, world!</P>
<SYNC Start=4000><P Class=ENCC>&nbsp;</P>
<SYNC Start=4500><P Class=ENCC>This is a subtitle file.</P>
<SYNC Start=8000><P Class=ENCC>&nbsp;</P>
<SYNC Start=8500><P Class=ENCC>Converted locally!</P>
<SYNC Start=12000><P Class=ENCC>&nbsp;</P>
</BODY>
</SAMI>

Specification Sheet

SRT vs SMI Technical Specifications

Standard Compliant

Input Format

SRT

SRT (SubRip) is a plain-text subtitle format using sequential numbered entries with HH:MM:SS,mmm timestamps. Each cue contains a start time, end time, and one or more lines of dialogue. SRT is the de facto interchange format used by virtually every video player, smart TV, streaming platform, and subtitle editing tool.

Output Format

SMI

SMI (SAMI - Synchronized Accessible Media Interchange) is an HTML-like subtitle format that wraps caption cues inside SYNC Start elements using millisecond timestamps. SMI documents can embed CSS styling and can support multiple language tracks. This converter writes a minimal SAMI document with one English caption class and basic timing; you can edit the CSS or add additional language classes manually.

Format Differences

SRT uses sequential numbered entries (1, 2, 3...) with HH:MM:SS,mmm timestamps and plain text. SMI wraps cues in SYNC Start=milliseconds elements inside a SAMI document with HEAD, STYLE, and BODY sections.

SRT timestamps show hours:minutes:seconds,milliseconds (e.g. 00:01:30,500). SMI timestamps are pure millisecond offsets from video start (e.g. 90500).

SRT is a flat text file with one format. SMI is a structured document containing HEAD, STYLE, and BODY sections, allowing embedded CSS and multiple language tracks.

SRT files are typically 1-3 KB per minute of video. SMI files are 2-4x larger due to HTML overhead and required document structure.

SRT has no styling support. SMI supports CSS classes per SYNC element, enabling colored text, font changes, and per-cue positioning.

SRT cue text is normally plain UTF-8 text. SMI text lives inside P elements and can contain HTML-like markup, enabling manually authored inline formatting.

Conversion Troubleshooting & Gotchas

Practical solutions for player compatibility, character encoding, and timing synchronization

4 Common Gotchas

GOTCHA #1

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.

GOTCHA #2

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.

GOTCHA #3

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.

GOTCHA #4

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

Converts SRT HH:MM:SS,mmm timestamps to SMI millisecond offsets automatically

Wraps each cue in a SYNC Start element and follows it with a blank end SYNC element

Generates a minimal SAMI document with HEAD, STYLE, and BODY sections

Maintains cue line breaks and escapes the text safely for SAMI markup

Defines an ENCC caption class that you can customize in the generated CSS

Handles UTF-8 and multi-byte character sets used for Korean, Japanese, and Chinese subtitles

Client-side processing - no file uploads, so your subtitle content stays in your browser

Free with no sign-up, no watermarks, and files up to 50 MB each

Why Convert?

Some Korean media and archival workflows ask for SMI rather than SRT for subtitle delivery.

SAMI may be requested when an accessibility or archival workflow documents it as its accepted caption format.

SMI supports embedding multiple language tracks in a single file using CSS class switches, which SRT cannot do.

Some legacy Windows Media Player and corporate video deployments expect SAMI captions rather than plain-text SRT.

SMI allows inline CSS styling of caption text (font, color, positioning) without a separate styling file.

Older archival and playout workflows may still expect HTML-structured captions rather than plain SRT files.

Scenarios

Common Use Cases

Korean Media Workflows

Some Korean streaming and broadcast workflows still request SMI captions. Convert your SRT subtitles and review the output against the platform's current delivery requirements.

Accessibility Compliance

Use SMI when an accessibility workflow specifically lists SAMI as an accepted caption format. Conversion alone does not guarantee compliance, so review timing, text, and player behavior before delivery.

Multi-Language Caption Delivery

SMI can embed multiple language tracks in a single file using CSS class switching. Convert each SRT, then manually combine the language tracks if your workflow requires one multilingual SMI file.

Legacy System Migration

Older Windows Media Player deployments, corporate training systems, and archival platforms may still expect SAMI captions. Convert modern SRT subtitles for systems that specifically request this format.

Styled Caption Delivery

SMI supports CSS-based caption styling beyond plain SRT text. Convert to SMI when a workflow requires it, then edit the generated CSS and markup for any advanced presentation needs.

Format Ecosystem

Related Formats

VTT

WebVTT - the modern web standard for HTML5 video subtitles. Use VTT instead of SMI for modern web platforms and browsers.

SRT

SubRip - the universal subtitle interchange format. Most editing tools export SRT, which you then convert to SMI for specific platforms.

ASS

Advanced SubStation Alpha - a styled subtitle format popular in anime and karaoke. Use ASS when you need advanced styling beyond what SMI CSS offers.

How It Works

1
Upload or drag your SRT file into the converter area.
2
The parser reads each numbered entry, extracting start/end timestamps and subtitle text.
3
Timestamps in HH:MM:SS,mmm format are converted to integer millisecond offsets from video start.
4
Each cue is written as an ENCC paragraph inside a SYNC Start element, followed by a blank SYNC at the cue end time.
5
A minimal CSS style block defines the ENCC caption class for SMI-compatible players.
6
Download the resulting .smi file and review it before delivery to a platform or legacy system.

moreTools.fromFormat

SRT LRC SRT VTT SRT SBV SRT ASS SRT TXT SRT TTML SRT SCC SRT STL

moreTools.toFormat

VTT SMI ASS SMI LRC SMI SBV SMI SSA SMI TTML SMI SCC SMI STL SMI

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Frequently Asked Questions

SMI stands for Synchronized Accessible Media Interchange, an HTML-like subtitle format developed by Microsoft. It wraps subtitle cues inside SYNC Start=milliseconds elements within a SAMI document. SMI is still encountered in Korean media workflows and legacy Windows Media Player content.

SRT uses HH:MM:SS,mmm format (e.g. 00:01:30,500 meaning 1 minute 30.5 seconds). SMI uses pure millisecond offsets from the start of the video (e.g. 90500 for the same timestamp). The converter handles this conversion automatically for every cue.

The generated SMI file includes a CSS style block in the HEAD section that defines the ENCC caption class. You can edit this CSS to customize font, color, size, and positioning to match your player or delivery requirements.

You need SMI specifically when a Korean media workflow, accessibility portal, or legacy Windows Media system asks for .smi files. VTT is the modern web standard, but it is not a substitute when SAMI is the required delivery format.

Yes. SMI can contain multiple language tracks in one file using CSS class switches, and a player can let users choose between P elements with different language classes. This converter creates one ENCC track; you can add other language classes manually after conversion.

The converter writes UTF-8 text, which supports Korean, Japanese, Chinese, and other multi-byte character sets. The generated document does not include an explicit charset declaration, so check that your player or delivery workflow treats the file as UTF-8.

Ready to convert your subtitles?

Drop your SRT file here and convert to SMI instantly.

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