SUB Subtitle
Subtitles & CaptionsSUB can identify different subtitle formats, including text and VobSub images. VobSub can pair SUB with an IDX index. Identify the format/companions before treating it as editable SRT-like text.
- What it is used for
- Storage of text-based or image-based subtitles
- What the file contains
- Producer-dependent
All sections, questions and sources
Content reviewed： · Editor：Kai
Opening steps
Choose your environment or purpose to see its steps.
Menu labels and support vary by app, OS and version. Preserve the original before making changes.
Troubleshooting by symptom
- Unreadable as text: it may be image/binary subtitles; do not overwrite it as an encoding fix.
- Missing timing: check whether an IDX/other companion supplies index/timing information.
- Out of sync: frame-based and time-based formats differ; check video edition and frame rate.
- SUB alone fails: inspect its matching VobSub IDX.
- Text SUB drifts: inspect source and conversion frame rates.
- Empty text after conversion: check whether bitmap subtitles required OCR.
Identified SUB → SRT
- Use a compatible converter for text subtitles; image subtitles require an OCR step.
- Proofread OCR names, punctuation, wrapping and timing against the video; retain original companions.
- Record subtitle type and validate OCR text and timing.
Renaming cannot extract text from images. OCR may misrecognize text and does not preserve the original appearance equivalently.
Do not identify subtitle format solely by suffix
Choose a workflow from readability, matching IDX and provenance.
Source for these steps：Library of Congress · VobSub Subtitle File (.sub) / Library of Congress · SubRip Subtitle format (SRT) / Subtitle Edit Project · Optical Character Recognition / VideoLAN · Subtitles — VLC desktop user documentation
Separate frame-based timing from OCR
Frame-based timing needs the correct fps; bitmap OCR can introduce text errors.
Compare punctuation, numbers, names and breaks with source images and check sync at three positions.
Source for these steps：Library of Congress · VobSub Subtitle File (.sub) / Library of Congress · SubRip Subtitle format (SRT) / Subtitle Edit Project · Optical Character Recognition / VideoLAN · Subtitles — VLC desktop user documentation
Related-format differences
| Format | Main role | What to check |
|---|---|---|
| Text SUB | Text/frame-based cues | Syntax/fps |
| SUB + IDX | Bitmap subtitle pair | Preserve the pair |
| SRT | Recognized text captions | OCR proofreading |
Handling and security
Review privacy before online OCR and retain paired SUB/IDX originals together.
Questions and answers
Is every SUB text?
No; VobSub and other variants can be image-based.
Do I need the IDX?
Some formats require the paired index.
Can I rename it SRT?
Format-specific timing conversion or OCR is needed.
What if a text SUB’s frame rate is unknown?
Identify source video/timing conditions and validate synchronization before frame-to-time conversion.
What needs careful proofreading after bitmap OCR?
Compare names, numbers, similar glyphs and breaks with the source images, then validate sync.
Format facts: name, steward and MIME type
- Formal name
- Producer-specific subtitle file
- Steward / specification
- Subtitle format ecosystem
- MIME type
- Depends on the producer or server; an extension alone does not establish a MIME type.
Primary and official sources
- Official documentationVobSub Subtitle File (.sub)
Institutional reference describing image-based SUB and its IDX companion.
Library of Congress · Link checked： - Official documentationSubRip Subtitle format (SRT)
Documents SRT timing, caption blocks and encoding.
Library of Congress · Link checked： - Official documentationOptical Character Recognition
OCR for image subtitles such as PGS and VobSub.
Subtitle Edit Project · Link checked： - Official documentationSubtitles — VLC desktop user documentation
Load subtitles and select a subtitle track.
VideoLAN · Link checked：