What is the SUP file format?
.sup is a raster image file used to store video subtitles as bitmaps. .sup files are the standard bitmap subtitle stream on Blu-ray discs (the HDMV Presentation Graphics Stream, or PGS), and can also be demuxed from Blu-ray .m2ts disc images or remuxed into MKV containers. They can be supplied to translators preparing a localised version of a film.
A .sup file holds subtitles as pictures, not as readable text - each cue is a positioned bitmap rendered over the video frame. The binary stream is a sequence of timestamped segments, each starting with the two-byte magic PG: PCS (composition), WDS (window), PDS (palette), ODS (RLE-compressed bitmap), and END. Because the words are stored as images, .sup files cannot be edited in a text editor. They can be converted to plain text using an OCR program; Subtitle Edit, for example, converts a .sup directly to .SRT using its built-in OCR engine.
OCR (Optical Character Recognition) is a text recognition technology used to extract text from image files. OCR is used by various programs supplied with scanners, office applications, or archiving software. Modern OCR technology heavily relies on neural networks trained to recognize text. The comparable bitmap subtitle format for DVD is VobSub (.sub / .idx).
Security & safety
RISK: LOWA .sup is passive subtitle data (timestamped bitmaps) and contains no executable code, so opening one in a player or Subtitle Edit is safe. Two practical cautions: keep your media player updated, since malformed subtitle streams have historically triggered decoder bugs (the 2017 "Subtitle Hell" research); and avoid sketchy "SUP converter" or "SUP viewer" download sites that bundle adware - VLC, Subtitle Edit and MKVToolNix are the trustworthy free tools.
Format details
in a nutshell- DVD/SUP subtitle (legacy SUP) - Older DVD-ripping tools (SubRip/ProjectX era) exported subtitle bitmaps to a .sup with no PG header; also image-based and OCR'd to .srt.
Programs that open SUP files
Windows4 apps
SupRip
Free Legacy tool that OCRs a .sup to .srt; functional but Subtitle Edit's OCR is the modern, better-maintained choice. 
VLC media player
Open-source Play the video, then Subtitle > Add Subtitle File and pick the .sup (VLC renders PGS bitmaps). 
Subtitle Edit
Open-source Open the .sup, use the built-in OCR (Tesseract) to turn the bitmaps into editable text, then save as .srt. 
MKVtoolnix
Open-source Add the .sup as a subtitle track when muxing an MKV - keeps the original Blu-ray subtitles, selectable in players. 
macOS2 apps
VLC media player
Open-source Add the .sup as a subtitle file to the playing video; VLC renders the PGS bitmaps. 
Linux2 apps
Technical details
deep spec| Format type | Binary bitmap subtitle stream - subtitles are stored as images, not text |
| Developer | Blu-ray Disc Association - part of the HDMV Presentation Graphics Stream (PGS) specification |
| Byte order | Big-endian |
| File magic bytes | 0x50 0x47 (ASCII "PG") at offset 0 - marks the start of each PGS segment header |
| Compression | RLE (run-length encoding) applied to indexed-colour bitmap objects within ODS segments |
| Colour depth | 8-bit indexed - up to 256 colours per palette definition segment (PDS), with alpha transparency |
| Maximum resolution | 1920 × 1080 pixels (Blu-ray HD frame); each bitmap object occupies a positioned sub-region |
| Container origin | Raw PGS elementary stream demuxed from a Blu-ray M2TS disc track |
| Typical file size | 100 KB - 30 MB for a full film's subtitle track |
| Segment structure | Ordered stream of timestamped segments: PCS (composition), WDS (window), PDS (palette), ODS (bitmap), END |
| Encryption | None inside the .sup file itself; on-disc the carrying M2TS may be AACS-protected |
| MIME type | application/octet-stream |
| Related subtitle formats | .srt, .ass / .ssa (text-based); .sub / .idx (VobSub - the DVD-era equivalent bitmap format) |
| Platform support | Windows, macOS, Linux via software players and tools; hardware Blu-ray players and set-top boxes |
| Released | 2006 (Blu-ray Disc, HDMV Presentation Graphics Stream) |
| Latest version | N/A (stable as part of the Blu-ray HDMV spec) |
| Open standard | Yes · royalty-free |
| Specification | en.wikipedia.org |
SUP conversions
Community Q&A
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