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 difficult to set up, 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 required setup. 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 OCR language support, added multiple OCR 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. OCR accuracy varies by language, font, contrast and source quality, and the converter offers many OCR language options 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)
Filename-Based Language Suggestion
The converter checks common language codes in your filename and suggests an OCR language. A file named movie_spa.sup suggests Spanish OCR. You can always change the language before conversion.
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 prefer browser tools instead of desktop subtitle software
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.