Is the SRT to SMI conversion free?

Yes, completely free with no sign-up, no watermarks, and no file size limits. 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?

All subtitle text from the SRT file is preserved exactly as written. Line breaks within cues are maintained. The converter wraps the text in P elements inside each SYNC block, and you can optionally add HTML tags for further formatting.

Does the converter support styled or positioned SRT cues?

SRT itself does not support positioning or styling natively. The converter focuses on converting timing and text accurately. If your SRT file contains HTML-like tags (sometimes used in non-standard SRT), they are passed through to the SMI output as-is.

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 typical SYNC element looks like: Subtitle text here . The Start attribute is the millisecond offset, and the P element contains the caption text with an optional CSS class.

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?

Absolutely. All conversion happens client-side in your browser. No subtitle data, file contents, or metadata is ever transmitted to a server. Your files remain entirely 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?

There is no file size limit. The converter processes files entirely in your browser. For very large files (feature-length films with thousands of cues), processing may take a few seconds but will complete successfully.

Does the converter handle SRT files with overlapping timestamps?

Yes. Overlapping or closely-spaced timestamps are preserved in the SMI output. Each cue is converted independently with its own SYNC element, so the timing relationships in the original file are maintained.

Can I batch convert multiple SRT files to SMI?

This page converts one file at a time. For batch processing, you can use the Workspace feature to load multiple files and convert them sequentially through the pipeline.

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 Converter

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SRT

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!

SMI

<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>

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Supports .srt files up to any size

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How It Works

Upload SRT File

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About SRT to SMI

This converter transforms SubRip (SRT) subtitle files into SAMI (Synchronized Accessible Media Interchange) format. SMI is an HTML-based captioning standard originally developed by Microsoft that wraps subtitle cues inside SYNC elements with millisecond timing. While SRT remains the universal interchange format, SMI is still required by many Korean broadcasting platforms, government accessibility portals, and archival video systems that expect HTML-structured captions rather than plain-text subtitles.

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-based subtitle format that wraps caption cues inside SYNC Start elements using millisecond timestamps. SMI files are full HTML documents that can embed CSS styling, support multiple language tracks in a single file, and are required by Korean streaming platforms (Naver TV, KakaoTV), Windows Media Player, and some government accessibility portals.

Features

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

Wraps each subtitle cue in a properly formed SYNC Start HTML element

Generates valid SAMI document structure with required HEAD, STYLE, and BODY sections

Preserves all subtitle text exactly as written in the original SRT source

Optionally adds a CSS class tag to each SYNC element for styling flexibility

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

Client-side processing - no file uploads, complete privacy guaranteed

Free with no sign-up, no watermarks, and no file size limits

Why Convert?

Korean streaming platforms including Naver TV, KakaoTV, and many Korean OTT services require SMI rather than SRT for subtitle uploads.

Government accessibility portals in Korea and some Asian markets mandate SAMI format for caption compliance.

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

Legacy Windows Media Player and older corporate video systems only parse SAMI captions, not plain-text SRT.

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

Archival video systems built before 2015 often expect HTML-structured captions and reject plain SRT files.

Some broadcast playout servers in the Asian market use SMI as their preferred ingest caption format.

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 HTML elements inside a full HTML document.

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 HTML 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 always plain UTF-8 text. SMI text lives inside P elements and can contain HTML markup, enabling inline formatting like bold or italic tags.

Common Use Cases

Korean Streaming Platforms

Korean OTT services like Naver TV, KakaoTV, and Korean broadcasting network sites require SMI format for subtitle uploads. Convert your SRT subtitles before submitting to these platforms.

Government Accessibility Compliance

Government and educational accessibility portals in Korea and parts of Asia mandate SAMI format for closed captioning compliance. SMI conversion ensures your content meets regulatory caption requirements.

Multi-Language Caption Delivery

SMI supports embedding multiple language tracks in a single file using CSS class switching. Convert from SRT (one file per language) to SMI to deliver all languages in one file with user-selectable tracks.

Legacy System Migration

Older Windows Media Player deployments, corporate training video systems, and pre-2015 archival video platforms often only accept SAMI captions. Convert modern SRT subtitles for these legacy systems.

Styled Caption Delivery

SMI supports inline CSS styling per cue, enabling colored text, font customization, and positioning that SRT cannot do. Convert to SMI when you need styled captions without switching to a full authoring tool.

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.

Frequently Asked Questions

What is an SMI subtitle file?

SMI stands for Synchronized Accessible Media Interchange, an HTML-based subtitle format developed by Microsoft. It wraps subtitle cues inside SYNC Start=milliseconds elements within a complete HTML document. SMI is still widely used on Korean streaming platforms like Naver TV and KakaoTV, as well as in legacy Windows Media Player content.

How are timestamps different between SRT and SMI?

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.

Does the converter add CSS styling to the SMI output?

Yes. The generated SMI file includes a default CSS style block in the HEAD section that defines a basic caption style. You can edit this CSS to customize font, color, size, and positioning to match your platform requirements.

Why would I convert SRT to SMI instead of VTT?

You need SMI specifically when delivering to Korean streaming platforms, government accessibility portals, or legacy Windows Media systems. VTT is the modern web standard, but it is not accepted by platforms that require SAMI. If your target platform asks for .smi files, SRT-to-SMI conversion is the right path.

Can SMI files contain multiple languages?

Yes. One of SMI's biggest advantages over SRT is support for multiple language tracks in a single file using CSS class switches. Each SYNC element can contain multiple P elements with different language classes, and the player lets users switch between them. SRT requires separate files for each language.

Will Korean characters (Hangul) display correctly after conversion?

Yes. The converter preserves UTF-8 encoding, which is essential for Korean, Japanese, Chinese, and other multi-byte character sets. The SMI document includes a proper charset declaration so players render CJK text correctly.

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Drop your SRT file here and convert to SMI instantly.

Related Resources

What is SRT?What is SMI?