Convert SRT to SUP

Blu-ray authoring and some hardware-media workflows need a PGS subtitle stream rather than an editable text subtitle file. Converting an SRT to a .sup file renders each timed cue as a bitmap for muxing into Blu-ray-compatible video or an MKV file.

What SRT is

.srt is a plain-text subtitle format used by subtitle editors, web-video services, media players, and video encoders. Each cue contains a sequence number, start and end times, and one or more lines of text, for example 00:01:12,500 --> 00:01:15,000.

SRT is easy to revise in tools such as Subtitle Edit and Aegisub. It can carry limited inline formatting in some implementations, but it does not reliably define the font, glyph rendering, palette, exact screen placement, Blu-ray forced-display metadata, or bitmap appearance required by PGS.

What SUP is

For Blu-ray work, a .sup file normally means a Blu-ray PGS (Presentation Graphic Stream) subtitle track. PGS stores compressed bitmap images, palette data, positions, and presentation timestamps instead of editable text.

PGS is used in Blu-ray folders and discs and can be multiplexed into Matroska (.mkv) files. It preserves the selected font, outline, shadow, color, and placement on compatible players, including when a playback device lacks the required font or script.

A SUP file is much larger than its SRT source, and changing its wording later usually requires the original SRT or OCR. The .sup extension is also used by some non-PGS subtitle systems, so confirm that the destination specifically requires Blu-ray PGS/HDMV PGS.

Convert SRT to Blu-ray SUP

Subtitle Edit is the practical desktop option because it can render an SRT into Blu-ray PGS while providing font, palette, position, and video-preview controls.

1. Open the SRT in Subtitle Edit with File → Open.
2. Load the exact target video with Video → Open video file. Subtitles from a different release, cut, frame-rate conversion, or version with added logos can drift out of sync.
3. Correct timing, line breaks, spelling, and reading speed before export. Review every non-Latin character and symbol in the selected font.
4. Select File → Export → Blu-ray SUP, or the Blu-ray/PGS .sup export entry in the installed version.
5. Set the output canvas to the target video format, usually 1920×1080 for 1080p Blu-ray or 1280×720 for 720p material. Set a Unicode-capable font, font size, text and outline colors, outline width, shadow, and bottom margin.
6. Save the result as subtitles.sup and play it with the target video in VLC, mpv, or another player that reports PGS subtitle support.

To add the PGS track to an MKV without re-encoding video, open the video and subtitles.sup in MKVToolNix GUI, set the language and track name, then multiplex. For Blu-ray output, import the PGS stream into the authoring application or use a Blu-ray-compatible muxing workflow such as tsMuxeR where appropriate.

Browser converters such as Convertio can be used for small, non-sensitive test files if its current format list offers SRT-to-SUP output. Before relying on online output, inspect it with MediaInfo or test it in a PGS-capable player: services may expose a different subtitle format under the same .sup extension, and they provide less control over font, resolution, margins, and privacy.

Compatibility and quality limits

Use a font containing every required glyph for Arabic, CJK, Cyrillic, accented Latin text, and symbols. Missing characters become replacement glyphs or empty boxes in the rendered bitmap and cannot be fixed as editable text afterward.

Match the PGS canvas to the intended video resolution. Players can scale a mismatched stream, but subtitle thickness, safe-area margins, and placement can change.

SRT timestamps are time-based, but timing still must match the same edit. A subtitle timed for a 23.976 fps release may progressively drift against a 25 fps speed-up unless its timestamps are retimed before rendering.

Do not assume an SRT can identify individual forced subtitles. MKVToolNix's forced-display setting is normally a track-level flag, not a way to mark selected cues. For selected forced dialogue, create a separate forced PGS track or use Blu-ray authoring software that can set the required per-event PGS metadata.

PGS is suitable for Blu-ray players and many desktop players, but browser players and most streaming platforms usually require WebVTT, TTML, or text-based captions instead. Keep the original .srt as the editable master; PGS is a delivery format.