SRT to SMI Converter

The Complete Guide to Converting SRT to SMI (SAMI) Subtitles

Master the conversion of SubRip (.srt) subtitle files into Microsoft SAMI (.smi) closed captions. Discover how HTML-based SAMI architecture functions, how clock-based SRT timestamps translate into millisecond <SYNC> tags, how to generate clean end-time clearance markers, and how to optimize subtitle playback in Windows Media Player, GOM Player, and PotPlayer.

SubRip (.srt) is celebrated throughout the modern media landscape as the global standard for video subtitling. Its minimalist design—combining sequential cue numbers, clock timestamps formatted as hours, minutes, seconds, and milliseconds, and plain dialogue text—makes it effortlessly compatible with web players, mobile operating systems, streaming servers, and professional non-linear video editors like Adobe Premiere Pro and DaVinci Resolve.

However, specific media ecosystems, educational language software, legacy Windows environments, and major East Asian media players continue to rely fundamentally on Microsoft SAMI (.smi) files. Developed by Microsoft in 1998 for Windows Media Player, Synchronized Accessible Media Interchange (SAMI) uses an HTML-like document model with CSS styling, custom language classes, and millisecond-based <SYNC Start="..."> tags. In South Korea, SAMI (.smi) has remained a cornerstone format for two decades across popular players like GOM Player, PotPlayer, and KMPlayer.

When content creators, video translators, or media archivists need to deliver subtitles for platforms or users that demand the SAMI format, converting SRT to SMI becomes an indispensable workflow step. The conversion requires far more than changing the file extension: clock timecodes must be accurately computed into absolute millisecond integers, multi-line subtitles must be formatted with HTML line breaks (<BR>), document headers and CSS classes (.KRCC, .ENCC) must be configured, and crucial end-time clearance points (&nbsp;) must be inserted so subtitles do not linger indefinitely on screen.

This in-depth technical guide examines the structural distinctions between SRT and SMI, the mathematical conversion of timestamps, best practices for managing bilingual closed caption classes, command-line conversion techniques using FFmpeg, and troubleshooting solutions for common subtitle synchronization hurdles.

What is an SRT File and What is an SMI (SAMI) File?

A SubRip (.srt) file is a lightweight, line-oriented plain-text document designed exclusively for subtitle display. Each cue in an SRT file comprises three or four lines: a sequential counter (1, 2, 3...), a timeline range declaring explicit start and end clock times separated by an ASCII arrow (00:01:23,456 --> 00:01:27,890), one or more dialogue lines, and a blank line marking the conclusion of the cue. SRT files do not require document headers, XML wrappers, or styling declarations.

In stark contrast, a Microsoft SAMI (.smi or .sami) file is structured as a full HTML/XML document. It opens with an outer <SAMI> tag, contains a <HEAD> section with an embedded CSS style sheet (<STYLE TYPE="text/css">), and places all subtitle dialogue inside a <BODY> element. Crucially, each spoken line in a SAMI file is introduced by a <SYNC Start=#####> tag, where the timecode represents total elapsed milliseconds from the start of the video (for example, 83456 ms instead of 00:01:23,456).

Furthermore, SAMI associates every dialogue block with a specific CSS class tag (<P Class=KRCC>), which identifies the language track (such as Korean or English) and applies typographic rules including font face (Gulim, Batang, Arial), text color, font size, and text alignment. While SRT is lightweight and universally supported by modern web standards, SAMI offers structured CSS styling and built-in multi-track language tagging within a single file.

Why Convert SRT Subtitles to SMI / SAMI?

Explore the most common technical scenarios where converting SubRip (.srt) to Microsoft SAMI (.smi) is essential.

How to Convert SRT to SMI Online (Step-by-Step)

Follow these simple steps to transform your SubRip subtitle files into clean, player-ready Microsoft SAMI captions.

SRT vs. SMI: Comprehensive Format Comparison

Compare the architectural, temporal, and compatibility differences between SubRip and Microsoft SAMI.

Understanding SAMI Timestamps: From Clock Codes to Milliseconds

The mathematical principles behind converting SRT clock times into SAMI <SYNC> tags.

The defining technical challenge of converting SRT to SMI lies in how the two formats conceptualize timeline synchronization. SubRip specifies a closed time interval for every subtitle cue using the format HH:MM:SS,mmm --> HH:MM:SS,mmm. For example, a cue starting at 1 minute, 24 seconds, and 500 milliseconds and ending at 1 minute, 28 seconds, and 200 milliseconds is rendered as `00:01:24,500 --> 00:01:28,200`.

Microsoft SAMI, on the other hand, operates on an open-ended timeline governed by discrete event triggers. Instead of stating an end time directly, SAMI uses the `<SYNC Start=#####>` tag, where the value represents total milliseconds from the beginning of the stream. To calculate this value from an SRT start time, our converter uses the exact formula: StartMs = (Hours * 3,600,000) + (Minutes * 60,000) + (Seconds * 1,000) + Milliseconds. For 00:01:24,500, this yields (1 * 60,000) + (24 * 1,000) + 500 = 84,500 ms.

Because SAMI has no cue duration parameter, a subtitle displayed at <SYNC Start=84500> would remain permanently visible on screen until the next spoken subtitle triggers—unless an explicit clearance event is introduced. To ensure the subtitle vanishes exactly when intended (at 88,200 ms), the converter calculates the end time in milliseconds and inserts an empty sync event: `<SYNC Start=88200><P Class=KRCC>&nbsp;`. This elegant mechanism guarantees frame-accurate subtitle clearance in all SAMI-compliant players.

Managing Language Classes (.KRCC, .ENCC) in SAMI Files

How SAMI's CSS class architecture enables multilingual caption tracks.

One of the most powerful features of the Microsoft SAMI specification is its built-in capacity for multilingual closed captioning within a single unified file. In a SAMI document's `<STYLE>` block, creators declare specific CSS classes assigned to language codes. For instance, `.KRCC { Name: Korean; lang: ko-KR; SAMIType: CC; }` defines the primary Korean track, while `.ENCC { Name: English; lang: en-US; SAMIType: CC; }` defines the accompanying English track.

When our converter translates an SRT file to SMI, you can choose the precise language class applied to your subtitle cues. If you are preparing subtitles for a Korean audience using PotPlayer or GOM Player, selecting `KRCC` ensures that player caption renderers immediately recognize the dialogue as the primary Korean track and apply customized Korean typography (such as Gulim font smoothing).

Similarly, if you have two separate SRT files (one in English and one in Korean), you can convert both using corresponding language classes (`ENCC` and `KRCC`) and merge the sync blocks into a single bilingual SAMI file. Compatible media players then allow viewers to toggle between English subtitles, Korean subtitles, or display both simultaneously as split-screen learning captions.

Concrete Example: Converting SRT to SMI

Compare the original SubRip subtitle text against the converted Microsoft SAMI markup below:

1
00:00:01,200 --> 00:00:04,500
Hello and welcome to our video!
We hope you enjoy the presentation.

2
00:00:05,100 --> 00:00:08,800
Subtitles are synchronized in milliseconds.

<SAMI>
<HEAD>
<TITLE>Converted Subtitles</TITLE>
<STYLE TYPE="text/css">
<!--
P { font-family:gulim, sans-serif; font-size:14pt; text-align:center; color:white; }
.KRCC { Name:Korean; lang:ko-KR; SAMIType:CC; }
.ENCC { Name:English; lang:en-US; SAMIType:CC; }
-->
</STYLE>
</HEAD>
<BODY>
<SYNC Start=1200><P Class=KRCC>
Hello and welcome to our video!<BR>We hope you enjoy the presentation.
<SYNC Start=4500><P Class=KRCC>&nbsp;
<SYNC Start=5100><P Class=KRCC>
Subtitles are synchronized in milliseconds.
<SYNC Start=8800><P Class=KRCC>&nbsp;
</BODY>
</SAMI>

Line Breaks and HTML Formatting in SAMI

How multi-line subtitles and typography are preserved during conversion.

In standard SubRip (.srt) files, subtitle line breaks are indicated simply by physical newline characters (\n). However, because SAMI documents follow an HTML document object model, standard web parsers collapse consecutive whitespace and ignore carriage returns. If an SRT converter were to simply copy newlines into a SAMI file, media players would render multi-line dialogue as a single run-on sentence.

Our converter handles this gracefully by translating all newline characters within a subtitle cue into standard `<BR>` line break tags. Whether your subtitles contain two speakers marked by dashes (- Speaker 1 / - Speaker 2) or a long caption split across two visual tiers for readability, the exact two-tier visual layout is preserved.

Additionally, if your SRT file contains basic styling tags such as italics (`<i>...</i>`), bold (`<b>...</b>`), or underline (`<u>...</u>`), our converter can retain these tags directly inside the `<P Class=...>` body. Because SAMI natively supports HTML formatting tags, compliant players will render your emphasis styling accurately on screen.

Converting SRT to SMI via Command Line (FFmpeg)

Automate bulk subtitle conversion workflows using the open-source FFmpeg CLI.

ffmpeg -i input.srt -c:s sami output.smi

For developers, system administrators, and video engineers managing large video libraries, FFmpeg provides automated subtitle format conversion via terminal commands. The command `ffmpeg -i input.srt -c:s sami output.smi` reads your SubRip subtitle file and encodes it into a Microsoft SAMI (.smi) container.

To batch convert an entire folder of .srt files on Windows PowerShell, run: `Get-ChildItem *.srt | ForEach-Object { ffmpeg -i $_.FullName -c:s sami ($_.BaseName + '.smi') }`. On Linux or macOS terminal, use: `for f in *.srt; do ffmpeg -i "$f" -c:s sami "${f%.srt}.smi"; done`.

While FFmpeg is powerful for automated command-line scripts, its built-in SAMI muxer uses generic styling templates and does not allow interactive customization of language class names (.KRCC vs .ENCC) or clearance sync points. Our browser-based converter provides instant visual feedback, custom class assignment, and one-click copying without installing command-line tools.

Practical Use Cases for SRT to SMI Conversion

Discover the industries and environments that depend on accurate SRT to SAMI caption generation.

Troubleshooting Common SRT to SMI Conversion Issues

Resolve timing errors, overlapping subtitles, and player display glitches quickly.