How to convert Blu-ray PGS subtitles to text on a Mac
Blu-ray subtitles are pictures, not text. Here’s why that causes problems in a remux, and how to turn PGS subtitles into text subtitles on macOS.
Rip a Blu-ray or 4K Blu-ray and the subtitle tracks come across as PGS (Presentation Graphic Stream). Despite looking like ordinary subtitles on screen, PGS tracks are images: each line is a small picture laid over the video. That’s fine on a disc player, but in a library of files it gets in the way.
Why picture subtitles are a nuisance
- They can’t be restyled. The font, size and position are baked into the image. Your player can’t make them bigger or change the colour.
- They don’t fit every container. MKV carries PGS happily, but MP4 generally doesn’t, so they’re often lost if you remux a film to MP4.
- They can’t be searched or edited. You can’t fix a typo, or search for a line, in a picture.
- Some players have to burn them in. Where a player can’t overlay picture subtitles itself, the video may need to be transcoded on the fly to draw them in, which defeats the point of a lossless remux.
Text subtitles avoid all of that. They’re tiny, they can be styled by the player, and they work in more places.
How the conversion works
Turning pictures into text is optical character recognition (OCR): each subtitle image is read and its text written out with the same timing. The traditional route on a Mac means extracting the subtitle track with one tool, running it through a separate OCR program, correcting the output, and muxing the result back in.
Doing it with Remux Doctor
Remux Doctor handles that as one fix.
- Drop in your files. Each one is examined, and its subtitle tracks are listed by format in plain English, so you can see which are picture subtitles.
- Say you want text subtitles in your target. Every file with picture subtitles is then flagged.
- Fix. Remux Doctor reads the picture subtitles with Apple’s on-device text recognition and writes them as text. Nothing is uploaded; it all happens on your Mac.
As with every Remux Doctor fix, the result is a new file, checked before it’s kept, and the video is never re-encoded. Your original stays as it is.
A tip
OCR is very good on clean, standard subtitles, but no OCR is perfect. Italics, unusual fonts and song lyrics are where mistakes tend to creep in, so it’s worth spot-checking a film you care about.
If you’re also remuxing to MP4, Remux Doctor can do that in the same run, with each file’s fixes applied in the right order. Examining and checking your files is free, and your first three files can be fixed free; after that, converting subtitles is part of the one-time unlock. Remux Doctor is coming soon for Macs with Apple silicon.