TL;DR: A Blu-ray subtitle is usually PGS — a stream of subtitle images, one bitmap per line, each carrying its own start and end time, saved as a .sup file. Because a .sup holds pictures and not characters, most players and cloud drives can't display it, and no format converter can turn it into SRT. You OCR the images into text — GeekLink reads a .sup straight into a timed SRT on a Mac, locally.
What is a SUP (PGS) subtitle?
PGS — Presentation Graphic Stream — is the subtitle format used on Blu-ray discs. Every subtitle line is stored as a small rendered image of the text, together with the exact time it should appear and disappear, and the whole track is saved as a single .sup file. It is the Blu-ray counterpart of the DVD's VobSub: same idea (pictures, not characters), newer container.
Because the subtitle is a picture, there is no text inside the file to copy out, and a subtitle editor or player that expects SRT has nothing to read. A .sup is a sequence of images, so turning it into an editable SRT always needs OCR — not a format conversion, because there is no text in the file to convert.
Why won't my player or cloud drive load a .sup?
This is the reason most people go looking for the conversion. Lightweight players — phone apps, smart-TV players, and the built-in players inside cloud drives — only accept text subtitle files such as SRT. They have no OCR built in, so they simply cannot render a picture-based .sup track. You end up with a film that plays but shows no subtitle.
If your cloud drive plays the video but the subtitle never shows, and the subtitle file is a .sup, that is why: those players load SRT, not graphic subtitle tracks. Converting the .sup to SRT once, up front, is what makes the subtitle work everywhere you actually watch.
Converting SUP to SRT is an OCR job
The .sup images have to be read line by line to become text. On Windows, Subtitle Edit can run this OCR pass, but it reads the images one at a time and gets slow across a full film. The result, whichever tool you use, is a plain SRT that carries the same timings the .sup already had, now with editable text you can load in any player or hand to a translator.
A SUP-to-SRT tool does not "convert" a file — it OCRs each subtitle image and writes the recognized text into an SRT, keeping the original start and end times. That is why the timing comes out right without any manual syncing: every line already carried its own timestamp inside the .sup.
Why SUP OCR beats OCR-ing the video
There are two ways to OCR a Blu-ray subtitle, and they are not equally accurate. You can render the subtitle onto the video and OCR the frames, or you can OCR the .sup images directly. The second is far more reliable.
A .sup image is a clean subtitle bitmap on a transparent background — there is no film footage behind the text, so the OCR never has to separate letters from a busy, moving scene. That is the exact opposite of extracting hardcoded subtitles, where the text sits on top of the picture and the background is the hard part. It also means you should never render a .sup back onto the video first: doing so only adds a background the OCR then has to fight through.
Even a clean image can be misread, though — a thin outline or an unusual font can trip any OCR engine. That is why the useful part is being able to check it: GeekLink shows the original subtitle image next to each recognized line, so you can catch a wrong character at a glance and fix it, instead of trusting the output blind.
How do I do this on a Mac?
On a Mac, GeekLink converts a .sup directly — no rendering onto video, no cloud upload:
- Get the
.supoff the Blu-ray. Rip the disc with MakeMKV and demux the PGS track, or pull it out of an MKV with mkvextract. Either way you end up with a.supfile. - Drop the
.supinto GeekLink. It OCRs each subtitle image into text and writes a timed SRT, locally on your computer, with nothing uploaded. - Review and fix. GeekLink lays the original subtitle image beside each recognized line, so you can spot and correct any OCR slip, adjust a timing if needed, and save.
- Translate or reuse. From the SRT you can translate into 40+ languages, export a bilingual file, or just load the SRT next to the video in any player or cloud drive.
GeekLink runs the whole thing locally and offline, so a full film — or a box set of episodes queued together — is converted on your own machine, with nothing sent to a server. If your source is a DVD rather than a Blu-ray, its subtitles are VobSub instead of PGS; the idea is the same, and the workflow is covered in extract subtitles from a DVD.
FAQ
What is a .sup file?
It is a Blu-ray PGS subtitle track — a stream of subtitle images, each with its own start and end time. Because it is image-based, it needs OCR to become an editable SRT.
Can I just rename or convert a .sup to .srt?
No. A .sup holds pictures, not text, so renaming does nothing and no format converter can pull out text that is not there. Only OCR turns the subtitle images into an SRT.
Why does my cloud drive play the video but show no subtitle?
Cloud-drive players load text subtitle files like SRT, not graphic .sup tracks. Convert the .sup to SRT once and load that SRT alongside the video instead.
Is OCR-ing the .sup better than speech recognition?
For an official Blu-ray, yes in one sense: the .sup is the exact subtitle the studio put on screen, so OCR-ing it preserves the original wording, whereas speech recognition re-transcribes the audio and can differ from the on-screen text. OCR can still misread a character, which is why reviewing the result against the original image matters.
Does this work offline?
Yes. GeekLink OCRs the .sup locally on your Mac. The subtitle images and the resulting SRT never leave your computer.