Does the converter handle VTT voice tags?

VTT voice tags (v Speaker) are used to label dialogue by speaker. Since SMI has no native voice tag syntax, the converter preserves the speaker label as plain text within the caption output so no information is lost.

Will the SMI output work on Korean streaming platforms?

Yes. The converter generates a valid SAMI document with proper HTML structure, CSS styling, and millisecond timestamps. The output .smi file is compatible with Korean streaming platforms that accept SAMI uploads.

Can I embed multiple languages in one SMI file from multiple VTT files?

SMI supports multi-language tracks via CSS class switching, but this converter processes one VTT file at a time. After converting each language separately, you can manually merge them into a single multi-language SMI file using the CSS class system.

Is the VTT to SMI converter free?

Yes, it is completely free with no sign-up, no watermarks, and no file size limits. All processing happens in your browser - no files are uploaded to any server.

Can I convert VTT to SMI on my phone?

Yes. The converter runs in any modern mobile browser. Open the page on iOS or Android, upload your VTT file, and download the converted SMI directly.

What happens to the WEBVTT header line?

The WEBVTT header (the first line of every valid VTT file) is removed during conversion. SMI files start with the SAMI root element instead, so the VTT header has no place in the output.

Does the output include CSS styling?

Yes. The generated SMI document includes a STYLE block in the HEAD section with a default caption class. You can edit this CSS to customize font, color, size, and positioning for your target platform.

Are timestamps accurate after conversion?

Yes. Each VTT timestamp is converted to a precise millisecond offset. For example, 00:01:30.500 becomes Start=90500. Both start and end times are converted, preserving exact cue durations.

Absolutely. All conversion happens client-side in your browser. No subtitle data, file contents, or metadata is ever sent to a server.

What if my VTT file has regions or complex positioning?

VTT regions and complex multi-line positioning are simplified in the SMI output. SMI positioning is less flexible than VTT regions, so advanced layouts may be approximated. Basic positioning and alignment are preserved accurately.

Can I edit the SMI file after downloading?

Yes. SMI files are HTML documents and can be opened in any text editor. You can modify CSS styles, add language tracks, adjust timing, or edit text content directly.

What character encoding does the output use?

The output uses UTF-8 encoding, which supports Korean (Hangul), Japanese, Chinese, Arabic, and all major scripts. The SMI document includes proper charset declaration for correct rendering.

How does VTT-to-SMI differ from SRT-to-SMI conversion?

VTT uses dot-separated timestamps and has richer features (cue styling, NOTE comments, voice tags, regions) that need to be handled during conversion. SRT is simpler plain text with comma-separated timestamps. Both produce the same SMI output format, but the VTT path handles additional syntax that SRT does not have.

VTT to SMI Converter

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VTT

WEBVTT
 
00:00:01.000 --> 00:00:04.000
Hello, world!
 
00:00:04.500 --> 00:00:08.000
This is a subtitle file.
 
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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How It Works

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About VTT to SMI

This converter transforms WebVTT (.vtt) subtitle files into SAMI (.smi) format. WebVTT is the W3C standard for HTML5 video captions, widely used by YouTube, Netflix, and modern browsers. SAMI is an older HTML-based format developed by Microsoft that is still required by Korean streaming platforms and legacy systems. Converting from VTT to SMI bridges the gap between modern web subtitle standards and platforms that have not yet migrated away from SAMI.

Input Format

VTT

VTT (WebVTT) is the W3C standard subtitle format for HTML5 video, supported natively by all modern browsers via the track element. It uses HH:MM:SS.mmm timestamps (with a dot separator, unlike SRT's comma), supports cue styling, positioning, voice tags, and is used by YouTube, Vimeo, Netflix, and other major streaming platforms.

Output Format

SMI

SMI (SAMI - Synchronized Accessible Media Interchange) is an HTML-based subtitle format developed by Microsoft for Windows Media Player. SMI files use SYNC Start=milliseconds elements and are full HTML documents with embedded CSS. They are required by Korean streaming platforms (Naver TV, KakaoTV), legacy Windows Media systems, and some government accessibility portals.

Features

Converts VTT dot-separated timestamps (HH:MM:SS.mmm) to SMI millisecond offsets

Strips VTT-specific syntax (WEBVTT header, NOTE blocks, cue identifiers) cleanly

Transfers VTT cue positioning and styling hints into SMI CSS class attributes

Wraps each cue in a SYNC Start element inside a valid SAMI HTML document

Generates a complete HTML document with HEAD, STYLE, and BODY sections

Handles VTT voice tags by preserving speaker labels in output text

Maintains UTF-8 encoding for Korean, Japanese, Chinese, and Arabic subtitle text

Client-side processing - no uploads, no server, complete data privacy

Why Convert?

Korean streaming platforms (Naver TV, KakaoTV, Wavve) accept SMI but not VTT for subtitle uploads, requiring conversion from the modern web standard.

Legacy Windows Media Player and Silverlight-based video players parse SAMI captions natively but cannot read WebVTT files.

SMI supports multiple language tracks within a single file using CSS class switching, while VTT requires separate files per language via the srclang attribute.

Corporate and educational video systems built on older Microsoft infrastructure expect SMI captions and reject VTT uploads.

Government accessibility compliance in some Asian markets mandates SAMI format, not WebVTT, for closed captioning.

SMI allows embedded CSS styling in the document header, providing a self-contained styled caption file without external styling references.

Archival and broadcast workflow systems in the Asian market often use SMI as their standard ingest format rather than the newer VTT.

Format Differences

VTT uses dot-separated timestamps (00:01:30.500). SMI uses pure millisecond offsets (Start=90500) in SYNC elements, with no human-readable time format.

VTT starts with a mandatory WEBVTT header line and optional metadata. SMI is a full HTML document starting with a SAMI root element containing HEAD and BODY.

VTT supports inline cue settings like line, position, align, and size. SMI handles positioning through CSS classes defined in the document STYLE block.

VTT uses NOTE blocks for comments and cue identifiers for referencing. SMI has no comment or identifier system; all cues are pure SYNC elements.

VTT voice tags inline speaker labels. SMI has no native voice tag support, so speaker labels are preserved as plain text within the caption.

VTT files are typically smaller (similar to SRT in size). SMI files are larger due to HTML document overhead, CSS blocks, and SYNC element structure.

Common Use Cases

Korean Platform Delivery

Korean streaming services like Naver TV, KakaoTV, and Wavve require SMI format. If your subtitles are in WebVTT (the YouTube/web standard), convert them to SMI before uploading to these platforms.

Legacy Windows Media Migration

Corporate training video systems and older Windows Media Player deployments cannot read WebVTT. Convert your modern web-standard VTT subtitles to SAMI for these legacy environments.

Accessibility Compliance

Government and educational accessibility portals in Korea and parts of Asia mandate SAMI format captions. Convert your VTT subtitles to SMI to meet compliance requirements.

Multi-Language Caption Files

SMI supports multiple language tracks in one file using CSS classes, while VTT requires separate files per language. Convert and merge VTT subtitles into a single multi-language SMI file for streamlined delivery.

Styled Caption Delivery

SMI embeds CSS styling directly in the document header, creating self-contained styled caption files. Convert VTT subtitles to SMI when you need a single file with embedded styling for archival or distribution.

Related Formats

SRT

SubRip - the universal plain-text subtitle format. A simpler alternative to VTT when you just need basic timing and text without web-specific features.

VTT

WebVTT - the input format for this converter, the modern W3C standard for HTML5 video captions.

ASS

Advanced SubStation Alpha - a feature-rich styled subtitle format for anime and professional captioning with advanced positioning and effects.

Frequently Asked Questions

What is the difference between VTT and SMI subtitles?

VTT (WebVTT) is the modern W3C web standard for HTML5 video, using dot-separated timestamps and supported by all browsers. SMI (SAMI) is an older Microsoft format using HTML-based SYNC elements with millisecond timestamps. VTT is the web standard; SMI is still required by Korean platforms and legacy systems.

How does the converter handle VTT timestamp format?

VTT uses dot-separated timestamps (00:01:30.500), while SMI requires pure millisecond offsets. The converter parses each VTT timestamp, converts it to the total milliseconds from video start, and writes it as the Start attribute of the SYNC element (e.g., 90500).

Are VTT NOTE comments preserved in the SMI output?

No. VTT NOTE blocks are developer comments and are not part of the subtitle content. The converter strips them during processing, as SMI has no equivalent comment system within SYNC elements.

When should I convert VTT to SMI instead of SRT?

Convert VTT to SMI when your target platform specifically requires the SAMI format - typically Korean streaming services (Naver TV, KakaoTV), legacy Windows Media Player, or government accessibility portals. If you just need a universal format, SRT is usually a better choice than SMI.

What happens to VTT cue styling and positioning?

VTT cue settings (line, position, align, size) are mapped to CSS class attributes in the SMI output where possible. Since SMI handles all styling through CSS, the converter creates appropriate style entries to approximate the VTT positioning.

How are VTT cue identifiers handled?

VTT allows optional cue identifiers (text before the timestamp line). These are stripped during conversion because SMI SYNC elements do not support identifiers. Only the timing and text content are preserved.

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Related Resources

What is VTT?What is SMI?