SMI to SRT Converter Online

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

Master the conversion from Microsoft SAMI (.smi) caption files to universally compatible SubRip (.srt) subtitles. Learn how HTML-based SAMI architecture works, how to calculate precise end times from sync clear points, how to handle Korean EUC-KR / CP949 encodings without mojibake, and how to seamlessly import subtitles into Premiere Pro, DaVinci Resolve, Final Cut Pro, and VLC.

In the history of digital multimedia, subtitle formats have evolved alongside media playback architectures. In the late 1990s, Microsoft introduced the Synchronized Accessible Media Interchange (SAMI) specification, designated by the .smi or .sami file extension, to deliver rich, styled closed captioning for Windows Media Player. SAMI was revolutionary for its era: built on an HTML and CSS document model, it enabled web-like text styling, custom fonts, precise font sizing, color highlights, and multiple simultaneous language tracks.

Nowhere did the SAMI format achieve greater cultural and technical significance than in South Korea. During the broadband boom of the early 2000s, Korean fansubbing communities and media distributors adopted .smi as the undisputed national standard for television broadcasts, cinema releases, anime subtitling, and foreign language education. To this day, millions of Korean drama (K-drama) episodes, classic films, and video archives remain encoded exclusively in legacy SAMI (.smi) files.

However, modern video workflows have shifted entirely toward open, lightweight, cross-platform standards. Today, SubRip (.srt) is the undisputed worldwide standard for subtitle interchange across media players like VLC and Plex, streaming giants like YouTube and Netflix, and professional non-linear video editing (NLE) platforms like Adobe Premiere Pro, DaVinci Resolve, and Apple Final Cut Pro. Almost none of these modern tools support the legacy Microsoft SAMI format.

Converting SMI to SRT bridges this crucial technical gap. Because SAMI relies on complex HTML markup, millisecond timestamps without end-times, and legacy character encodings like EUC-KR and CP949, manual conversion is fraught with timing errors and corrupted text. This comprehensive technical guide details the inner architecture of SAMI and SRT files, the mathematics of converting millisecond sync tags into clock timecodes, character encoding solutions, command-line automation, and best practices for modern playback and video editing.

What is an SMI (SAMI) File? Architecture of Microsoft's Subtitle Standard

An SMI (.smi) file, also known by its full acronym SAMI (Synchronized Accessible Media Interchange), is a structured, plain-text document based on HTML and XML syntax. Microsoft published the SAMI 1.0 specification in 1998 as part of its Windows Media technologies to provide synchronized accessibility text, audio descriptions, and multilingual captioning for digital video and audio streams.

Structurally, an SMI file mirrors a traditional HTML web page. It begins with an opening <SAMI> tag, contains a <HEAD> section featuring embedded CSS style sheets (<STYLE TYPE="text/css">), and encloses all subtitle cues within a <BODY> section. Within the CSS header, authors define visual typography such as font family (commonly Gulim, Batang, Arial, or sans-serif), text color, font size, margin spacing, and custom CSS classes. Crucially, each language track is declared as a unique CSS class—such as .KRCC for Korean Closed Captions, .ENCC for English, or .JPCC for Japanese.

Within the document's <BODY>, subtitle cues are sequenced using <SYNC Start=#####> tags, where the Start attribute represents the appearance time in absolute milliseconds from the beginning of the video timeline (e.g. <SYNC Start=15200> for 15.2 seconds). Immediately following the sync tag, a paragraph tag (<P Class=KRCC>) specifies which language track is speaking, followed by the subtitle text. Line breaks are rendered using HTML <BR> tags.

SubRip (.srt), by comparison, was engineered as a streamlined, standalone subtitle format completely decoupled from HTML document trees. An SRT file uses simple numbered counter blocks (1, 2, 3...), clock-based timestamps declaring both start and end times joined by an arrow delimiter (00:00:15,200 --> 00:00:18,500), dialogue text, and blank line separators. Because SRT is universally implemented in every media playback library (FFmpeg, Libass, GStreamer), converting SMI to SRT unlocks effortless playback on any device.

Why Convert SMI Subtitles to SRT?

Discover the critical advantages of converting legacy SAMI (.smi) captions into universally compatible SubRip (.srt) subtitles.

How to Convert SMI to SRT Online in 3 Simple Steps

Follow these step-by-step instructions to convert your SAMI subtitle files into valid SubRip SRT subtitles in seconds.

Technical Comparison: SMI (SAMI) vs. SubRip (SRT)

Examine the architectural and structural differences between Microsoft's SAMI format and universal SubRip subtitles.

Korean SMI Files: Solving EUC-KR and CP949 Mojibake Problems

Understand why Korean subtitles often display as corrupted symbols and how our converter guarantees flawless Hangul text.

One of the most persistent and frustrating challenges when handling Korean SMI subtitles is the phenomenon known as 'mojibake'—where beautifully written Korean Hangul characters appear as random accented European letters (such as '¿©±â', '¾È³çÇϼ¿ä'), geometric shapes, or question marks.

This corruption occurs because of historical character encoding standards. During the late 1990s and 2000s in South Korea, Windows computers predominantly saved text files using Microsoft's Code Page 949 (CP949, also known as Unified Hangul Code / UHC), an extension of the EUC-KR 8-bit character encoding. Unlike modern UTF-8 Unicode, which uses variable-length multi-byte sequences to represent all world languages universally, CP949 assigns Korean characters to specific two-byte hex combinations.

When a modern operating system (macOS, iOS, Android, Linux) or international software (VLC, Plex, Adobe Premiere Pro) attempts to read a CP949 file, it assumes the file is encoded in modern UTF-8 or Western Windows-1252. Because the binary bytes do not match UTF-8 sequences, the text decoder misinterprets the bytes, rendering corrupted gibberish.

Our online converter solves this problem at the browser level. Using modern HTML5 FileReader APIs and TextDecoder specifications, our tool natively supports EUC-KR, CP949, and UTF-8 decoding. You can select your file's original encoding with a single click, and our converter accurately translates the raw bytes into crystal-clear Korean Hangul, exporting pristine UTF-8 SubRip (.srt) files that display perfectly on every modern screen.

How SMI Timestamps Work: The Mechanics of End-Time Calculation

Learn how our parser transforms single millisecond sync tags into compliant SRT start and end intervals.

A fundamental difference between SAMI and SRT subtitle formats lies in how cue durations are declared. In an SRT file, every subtitle cue explicitly specifies its exact beginning and end: '00:01:14,250 --> 00:01:17,800'. In contrast, a SAMI file only records the start time in milliseconds: '<SYNC Start=74250>'.

To display subtitles accurately, media players must know when the text should disappear. In professional SAMI authoring, cue clearance is accomplished using a subsequent <SYNC> tag containing an empty paragraph or non-breaking space: '<SYNC Start=77800><P Class=KRCC>&nbsp;'. When the media player reaches 77,800 milliseconds, the empty text clears the screen.

However, real-world SAMI files frequently contain formatting inconsistencies. Some files omit clear tags entirely, relying on the next speaker's dialogue to replace the previous cue. In scenes with prolonged silence, music, or dramatic pauses, simply using the next dialogue cue's start time would cause the previous dialogue line to linger on screen for dozens of seconds or even minutes.

Our conversion engine implements intelligent end-time deduction: (1) If a subsequent clear point (<SYNC ...>&nbsp;) exists, its Start millisecond becomes the exact end timestamp. (2) If another dialogue cue follows shortly after, its start time becomes the end time. (3) If the gap between cues exceeds a natural threshold (or if the cue is the final subtitle in the file), our algorithm calculates a natural reading duration based on character length (approximately 15–20 characters per second, bounded between 1.8 and 7.0 seconds). This guarantees that every subtitle cue appears and disappears with natural, professional cadence.

Side-by-Side Example: SAMI Input vs. SubRip Output

Compare the verbose HTML structure of a Korean SAMI subtitle file with the clean, streamlined SubRip SRT output produced by our converter:

<SAMI>
<HEAD>
<TITLE>Korean Drama Episode 01</TITLE>
<STYLE TYPE="text/css">
<!--
P { font-family:gulim, sans-serif; font-size:14pt; color:white; }
.KRCC { Name:Korean; lang:ko-KR; SAMIType:CC; }
.ENCC { Name:English; lang:en-US; SAMIType:CC; }
-->
</STYLE>
</HEAD>
<BODY>
<SYNC Start=1500><P Class=KRCC>
안녕하세요! 오늘 날씨가 참 좋네요.
<SYNC Start=4800><P Class=KRCC>&nbsp;
<SYNC Start=6200><P Class=KRCC>
네, 정말 산책하기 좋은 날씨예요.<BR>우리 공원에 갈까요?
<SYNC Start=10500><P Class=KRCC>&nbsp;
</BODY>
</SAMI>

1
00:00:01,500 --> 00:00:04,800
안녕하세요! 오늘 날씨가 참 좋네요.

2
00:00:06,200 --> 00:00:10,500
네, 정말 산책하기 좋은 날씨예요.
우리 공원에 갈까요?

Bilingual SMI Files: Managing Dual-Language Tracks (KRCC & ENCC)

How our converter gracefully handles multi-language SAMI files without mixing or losing dialogue text.

A unique feature of SAMI files popularized by Korean translation groups is embedded bilingual captioning. In educational releases, foreign movie imports, and language-learning broadcasts, each dialogue exchange often includes two simultaneous paragraph tags: '<SYNC Start=5000><P Class=KRCC>안녕하세요!<P Class=ENCC>Hello!'.

If you attempt to convert such a file using naive search-and-replace scripts, both language lines may end up jumbled together into the same subtitle cue, resulting in cluttered three- or four-line subtitles that overwhelm the viewer. Worse, some basic converters simply discard the second language class entirely, causing silent data loss.

Our converter inspects the CSS class declarations inside the file and gives you full control over multilingual extraction: (1) All Tracks: Combines both lines cleanly with standardized spacing. (2) Specific Language Extraction: Allows you to isolate only the Korean track (.KRCC) or only the English track (.ENCC) into its own dedicated .srt file. This flexibility lets you generate separate subtitle files (e.g. video.ko.srt and video.en.srt) perfect for multi-track streaming on Plex or YouTube.

Command-Line Automation: Converting SMI to SRT Using FFmpeg

Execute fast batch subtitle conversions directly from your terminal or command prompt using FFmpeg.

ffmpeg -sub_charenc CP949 -i input.smi -c:s srt output.srt

For video engineers, server administrators, and power users with large collections of subtitle archives, the open-source multimedia framework FFmpeg provides built-in command-line subtitle conversion capabilities.

To convert a standard UTF-8 encoded SMI file, use: 'ffmpeg -i input.smi -c:s srt output.srt'. FFmpeg will parse the sync points and export a standard SubRip subtitle track.

If your input file is a legacy Korean SAMI file encoded in CP949 / EUC-KR, you MUST explicitly tell FFmpeg which character encoding to read using the '-sub_charenc' flag: 'ffmpeg -sub_charenc CP949 -i input.smi -c:s srt output.srt'. Failing to supply the sub_charenc parameter will result in corrupted mojibake characters in the output file.

While FFmpeg is extraordinarily powerful for automated batch scripts across hundreds of files, our browser-based online tool offers the exact same mathematical parsing precision without requiring command-line installations, terminal configuration, or binary downloads.

Common Real-World Use Cases for SMI to SRT Conversion

Discover how creators, translators, and media archivists rely on SMI to SRT conversion every day.

Troubleshooting Common SMI to SRT Conversion Issues

Diagnose and resolve common problems encountered when converting legacy SAMI files.