About Sup to Srt

A free, privacy-first subtitle converter built for Blu-ray enthusiasts, translators, and media server users.

Who We Are

We are a small team of subtitle enthusiasts and software developers who care deeply about privacy, open-source technology, and making powerful tools accessible to everyone — without paywalls or sign-up forms.

Our backgrounds span video production, media server management, and web development. We built Sup to Srt because we kept running into the same problem: existing SUP-to-SRT converters were either Windows-only, required server uploads, or charged for a feature that should be simple and free.

We believe your subtitle files are yours. They should never touch a stranger's server just to be converted. That belief is baked into every line of code we write.

Our Story

Sup to Srt started as a personal project. One of our team members was building a Plex library from a Blu-ray collection and needed a way to extract and search subtitles — without sending every file to a cloud service or being locked into a single operating system.

The existing options were frustrating. Desktop tools were Windows-only. Online converters uploaded files to remote servers. Command-line approaches worked but required technical knowledge most people don't have. There was no simple, private, cross-platform solution.

So we built one. We combined a hand-written JavaScript PGS parser with WebAssembly-powered Tesseract OCR and wrapped it in a clean, no-friction interface. The first working version ran entirely in the browser with no server involved at all.

Since then, we've expanded language support to 40+ languages, added multiple OCR accuracy profiles, and refined the post-processing pipeline based on real-world feedback from translators, archivists, and home theater enthusiasts around the world. Sup to Srt remains free, open, and private — just as it was on day one.

What Is Sup to Srt?

Sup to Srt is a free, browser-based tool that converts PGS (Presentation Graphic Stream) subtitle files — also known as .sup files — into editable SRT (SubRip Text) format using Optical Character Recognition (OCR).

Unlike server-side converters, Sup to Srt processes everything inside your browser. Your subtitle files are never uploaded to any server. Conversion happens entirely on your device using WebAssembly-powered OCR.

The Tool

Tesseract OCR Engine

Sup to Srt uses Tesseract OCR — the industry-standard open-source OCR engine originally developed by HP and now maintained by Google. Tesseract achieves 95–99% accuracy for Latin-script languages and supports 40+ languages including Arabic, Japanese, Korean, Chinese, and more.

PGS Parser

The converter includes a full PGS stream parser written in JavaScript. It reads the binary PGS format, decodes RLE-compressed subtitle images, applies YCbCr-to-RGB color conversion, and renders each subtitle frame as a canvas image for OCR processing.

Privacy by Design

No file ever leaves your browser. The OCR engine loads from a CDN once and runs locally via WebAssembly. There are no server-side logs of your subtitle content, no accounts, and no tracking beyond standard web analytics.

OCR Profiles

Three OCR accuracy profiles let you trade speed for precision:

  • Fast: Quick processing for clean, standard subtitle fonts
  • Balanced: Best for most users — reliable and reasonably fast
  • Accurate: Maximum recognition accuracy for stylized fonts or low-quality source images

Post-Processing Options

Built-in cleanup options improve output quality:

  • Preserve original line breaks
  • Remove common OCR artifacts (misread characters, stray symbols)
  • Smart punctuation normalization
  • Forced captions filter (for films with foreign-language inserts)

Language Auto-Detection

The converter detects the subtitle language from your filename. A file named movie_spa.sup automatically selects Spanish OCR. You can always override the detection.

Supported Languages

English, Arabic, Belarusian, Bengali, Bulgarian, Catalan, Chinese (Simplified & Traditional), Croatian, Danish, Dutch, Estonian, Finnish, French, German, Greek, Hebrew, Hindi, Hungarian, Icelandic, Indonesian, Irish, Italian, Japanese, Korean, Norwegian, Persian, Polish, Portuguese, Romanian, Russian, Serbian, Spanish, Swedish, Tamil, Telugu, Thai, Turkish, Ukrainian, Urdu, Vietnamese.

Who Is This For?

  • Blu-ray collectors who archive discs and want searchable SRT subtitles for Plex or Jellyfin
  • Subtitle translators who need to convert PGS source material to editable text
  • Language learners who want to use Blu-ray movie subtitles with learning apps
  • Media server users who want to reduce transcoding load by using text-based subtitles
  • Accessibility advocates who need editable captions for customization
  • Mac and Linux users who can't use Windows-only tools like Subtitle Edit

Limitations

Sup to Srt has a few limitations to be aware of:

  • OCR is not perfect. Accuracy depends on font quality, language, and image resolution. Always review converted subtitles for critical use cases.
  • One file at a time. Batch conversion is not supported. For bulk processing, use command-line tools like FFmpeg and Tesseract directly.
  • 100MB file limit. Very large SUP files (rare) may exceed the browser processing limit.
  • No formatting preservation. PGS subtitle styling (colors, positioning, font size) is not carried over to SRT.

Get in Touch

Have a question, found a bug, or want to suggest an improvement? Visit our Contact page to reach out.