How to Convert DVD Subtitles (SUB/IDX) to Editable Text

Want to edit, translate, or fix DVD subtitles but they're locked as images? This comprehensive guide explains how to convert image-based DVD subtitles (SUB/IDX and SUP formats) to editable SRT text format using OCR (Optical Character Recognition) technology.

Quick Summary

Problem: DVD/Blu-ray subtitles are images (SUB/IDX, SUP), not editable text
Solution: Use OCR (Optical Character Recognition) to convert images to text
Process: Extract subtitle files → Upload to converter → Select language → OCR → Download SRT
Time Required: 5-15 minutes depending on subtitle length
Accuracy: 95-99% for Latin scripts, 85-95% for Asian languages

Understanding Image-Based Subtitles

DVD and Blu-ray discs don't store subtitles as text — they use bitmap images instead. This means each subtitle line is literally a picture burned into the disc.

Why Do DVDs Use Image Subtitles?

Font control: Movie studios can use custom fonts and styling
Position control: Subtitles can be placed anywhere on screen
Graphics support: Can include studio logos or special symbols
Copy protection: Harder to extract and distribute than text files
Universal compatibility: DVD/Blu-ray players only need to display images, not parse text

Types of Image-Based Subtitle Formats

Image-Based vs Text-Based Subtitles

Feature	SUB/IDX (DVD)	SUP (Blu-ray)	SRT (Text)
File Type	Two files (.sub + .idx)	Single file (.sup)	Single text file (.srt)
Subtitle Data	Bitmap images (VobSub format)	Bitmap images (PGS format)	Plain text
Source	DVD discs	Blu-ray discs	User-created or OCR output
Editable?	❌ No (images)	❌ No (images)	✅ Yes (text)
File Size	Large (10-50 MB for 2hr movie)	Very large (30-100 MB)	Tiny (50-200 KB)
Quality	SD resolution (720x480)	HD resolution (1920x1080)	Depends on player rendering
Searchable?	❌ No	❌ No	✅ Yes
Translatable?	❌ No	❌ No	✅ Yes
Player Compatibility	⚠️ Moderate (VLC, MPC-HC)	⚠️ Moderate (modern players)	✅ Universal (99%)
Conversion Method	OCR required → SRT	OCR required → SRT	Already text

What is OCR (Optical Character Recognition)?

OCR is technology that "reads" text from images, just like how you read text with your eyes. The software analyzes each subtitle image, recognizes letter shapes, and converts them to actual text characters.

How OCR Works for Subtitles

Image Extraction

Software extracts each subtitle frame as a separate PNG/BMP image with timestamp

Image Preprocessing

Enhance contrast, remove noise, apply filters to make text clearer for recognition

Character Recognition

Tesseract OCR engine analyzes letter shapes and matches them to known characters in selected language

Context Analysis

Use dictionary and language models to improve accuracy (e.g., "rn" looks like "m", context helps decide)

Text Output

Generate SRT file with recognized text and original timing from IDX/SUP file

Convert DVD Subtitles to Editable Text

Upload your SUB/IDX files and convert them to editable SRT format using our free OCR-powered converter. Supports 100+ languages.

Convert SUB/IDX to SRT

Step-by-Step: Converting SUB/IDX to SRT

Step 1: Extract SUB/IDX Files from DVD

Before conversion, you need to extract the subtitle files from your DVD. You'll need both files:

.sub file: Contains the actual bitmap images of subtitles (large file, 10-50 MB)
.idx file: Contains timing, positioning, and color palette information (small file, 10-100 KB)

Extraction Tools:

Windows

DVDFab: Professional tool (paid/trial)
DVD Decrypter: Free, old but works
MakeMKV: Free for 30 days

Mac/Linux

MakeMKV: Cross-platform
HandBrake: Free, open-source
mencoder: Command-line (advanced)

Step 2: Go to Our SUB/IDX Converter

Visit our SUB/IDX converter tool. It's completely free and requires no installation or signup.

Step 3: Upload Both SUB and IDX Files

Important: You MUST upload BOTH files together. The .sub file contains images, and the .idx file contains timing. The converter needs both to create a properly timed SRT file.

⚠️ Common mistake: Only uploading .sub file. This won't work! Always upload both .sub AND .idx.

Step 4: Select the Correct Language

This is the most critical step for accuracy. OCR engines are trained for specific languages, and selecting the wrong language will result in gibberish output.

How to Identify Subtitle Language:

Check filename: Often includes language code (e.g., movie_eng.idx = English, movie_spa.idx = Spanish)
Check disc menu: DVD menu usually lists available subtitle languages
Try extraction tool: MakeMKV and DVDFab show language names
Visual check: If you can read the subtitle images, you know the language

💡 Pro Tip: Multi-language DVDs

DVDs often have multiple subtitle tracks (English, Spanish, French, etc.). Make sure you extract and convert the correct language you need. Each track will have its own .sub/.idx pair, usually named like:

movie_eng.sub / movie_eng.idx → English
movie_spa.sub / movie_spa.idx → Spanish
movie_fre.sub / movie_fre.idx → French

Step 5: Wait for OCR Processing

OCR processing is computationally intensive and takes time:

Short subtitles: 30 minutes of dialogue = 2-3 minutes processing
Feature film: 90-120 minutes of dialogue = 5-10 minutes processing
Long content: 2+ hours = 10-15 minutes processing

Processing time depends on the number of subtitle lines, image quality, and language complexity.

Step 6: Download Your SRT File

Once OCR completes, you'll receive an SRT file that you can:

✅ Edit in any text editor (fix OCR errors)
✅ Adjust timing with our Sync Shifter tool
✅ Translate to other languages
✅ Use with any video player (VLC, MPC-HC, Plex)
✅ Upload to YouTube, Vimeo, streaming platforms

OCR Accuracy: What to Expect

OCR accuracy varies significantly based on language, font quality, and image resolution:

Language	DVD Quality	Blu-ray Quality	Common Errors
English	95-98%	98-99%	I/l confusion, rn→m, 0→O
Spanish/French/German	94-97%	97-99%	Accents (é→e), ñ→n, ü→u
Simplified Chinese	85-90%	92-95%	Similar characters (日→目)
Traditional Chinese	83-88%	90-94%	Complex strokes
Japanese	80-87%	88-93%	Kanji variations, small kana
Korean	87-92%	93-96%	Similar jamo (ㅇ→ㅁ)
Arabic/Hebrew	82-88%	90-94%	Connected letters, diacritics
Russian/Cyrillic	92-96%	96-98%	Latin lookalikes (В→B, Р→P)

Factors Affecting OCR Accuracy:

Image resolution: Blu-ray SUP (HD) is much clearer than DVD SUB/IDX (SD)
Font size: Larger fonts = better accuracy
Font style: Simple sans-serif fonts work best; decorative fonts cause errors
Image quality: Clean backgrounds and high contrast improve results
Language complexity: Languages with fewer similar characters have better accuracy

⚠️ Always Proofread OCR Output!

OCR is NOT 100% perfect. Even with 95% accuracy, a 2-hour movie with 1,000 subtitle lines means 50 errors you'll need to fix.

Recommended workflow:

Convert SUB/IDX to SRT with OCR
Watch video with generated subtitles
Note any errors (wrong words, missing punctuation)
Edit SRT file to fix mistakes
Save corrected version

Post-OCR Cleanup: Fixing Common Errors

After OCR conversion, you'll likely need to fix some errors. Here are the most common ones:

Common Error #1: Letter Confusion

❌ Wrong:

l → I (lowercase L vs uppercase i)
rn → m (r+n looks like m)
0 → O (zero vs letter O)
8 → B

✅ Fix manually

Use Find & Replace in text editor, but check context!

Common Error #2: Missing Punctuation

OCR often misses periods, commas, and apostrophes, especially in low-resolution images.

Solution: Use our SRT Cleaner tool to automatically fix common punctuation issues.

Common Error #3: Broken Words

Words split incorrectly: "hel lo" instead of "hello"

Solution: Manual proofreading required. No automated tool can reliably fix this.

Common Error #4: Timing Drift

Subtitles start in sync but gradually drift out of sync over time.

Solution: Use our Sync Shifter or Partial Shifter to fix timing.

Converting Blu-ray Subtitles (SUP)?

If you have Blu-ray SUP files instead of DVD SUB/IDX, use our dedicated SUP to SRT converter. Higher resolution means better OCR accuracy!

Convert SUP to SRT

Blu-ray SUP vs DVD SUB/IDX

If you're working with Blu-ray discs, you'll encounter SUP files instead of SUB/IDX:

DVD SUB/IDX

Two files: .sub (images) + .idx (timing)
Resolution: 720x480 (SD)
Format: VobSub
OCR accuracy: 85-95%
File size: 10-50 MB per track

Blu-ray SUP

Single file: .sup (images + timing)
Resolution: 1920x1080 (HD)
Format: PGS (Presentation Graphic Stream)
OCR accuracy: 95-99% (higher res!)
File size: 30-100 MB per track

💡 Recommendation: If you have both DVD and Blu-ray versions, extract from Blu-ray for better OCR results.

Clean Up Your Converted Subtitles

After OCR conversion, use our SRT Cleaner tool to automatically fix common errors like extra spaces, broken formatting, and punctuation issues.

Clean SRT File

Frequently Asked Questions (People Also Ask)

What's the difference between SUB/IDX and SUP files?

SUB/IDX and SUP are both image-based subtitle formats, but from different disc types:

SUB/IDX (DVD Format):

Two files: .sub (bitmap images) + .idx (timing/index)
Format name: VobSub
Resolution: SD (720x480 NTSC or 720x576 PAL)
Source: DVD-Video discs
Color depth: 4-bit (16 colors)

SUP (Blu-ray Format):

Single file: .sup (contains both images and timing)
Format name: PGS (Presentation Graphic Stream)
Resolution: HD (1920x1080) or 4K (3840x2160)
Source: Blu-ray discs
Color depth: 8-bit (256 colors with transparency)

🎯 Key difference: SUP has much higher resolution (HD vs SD), resulting in better OCR accuracy when converting to text.

How accurate is OCR for subtitle conversion?

OCR accuracy ranges from 80-99% depending on multiple factors:

Excellent Accuracy (95-99%):

English subtitles from Blu-ray SUP files
Clean, simple sans-serif fonts
High contrast (white text on black background)
Large font size (>20pt)
HD resolution images

Good Accuracy (85-95%):

English from DVD SUB/IDX
Western European languages (Spanish, French, German)
Standard DVD subtitle quality

Moderate Accuracy (80-90%):

Asian languages (Chinese, Japanese, Korean)
Decorative or stylized fonts
Low contrast or colored backgrounds
Small font sizes

Real-world example:

A 2-hour English movie with 1,200 subtitle lines at 95% accuracy means approximately 60 errors that need manual correction. Plan 30-60 minutes for proofreading and fixing.

💡 Pro tip: Always select the correct language in the OCR tool. Wrong language selection can drop accuracy to 20-30%.

Can I convert Blu-ray subtitles to SRT?

Yes! Blu-ray subtitles use SUP format and can be converted to SRT using OCR, just like DVD subtitles.

Step-by-step process:

Extract SUP file: Use MakeMKV, BDInfo, or eac3to to extract .sup subtitle track from Blu-ray disc
Upload to converter: Use our SUP to SRT converter
Select language: Choose correct language for OCR
Wait for processing: OCR takes 5-15 minutes depending on length
Download SRT: Get editable text subtitle file

✅ Advantages of converting Blu-ray SUP:

Better OCR accuracy: HD resolution (1920x1080) vs DVD SD (720x480)
Clearer text: Sharper fonts, better anti-aliasing
Fewer errors: Typically 95-99% accuracy vs 85-95% for DVD
Single file: Only one .sup file vs two .sub/.idx files

💡 Recommendation: If you own both DVD and Blu-ray versions, extract subtitles from Blu-ray for best results.

Why is my OCR output gibberish?

OCR producing gibberish is almost always caused by selecting the wrong language. Here's how to diagnose and fix:

❌ Common Causes of Gibberish:

Wrong language selected: Trying to OCR French subtitles with English language model
Wrong script selected: Using Latin OCR for Cyrillic/Arabic text
Multi-language subtitles: Subtitles contain mixed languages (e.g., English + Chinese)
Corrupted image data: SUB/IDX files are damaged or incomplete

How to fix:

Verify subtitle language:
- Check DVD menu or disc case
- Look at extracted filename (movie_eng.sub = English)
- Use image viewer to open .sub file and visually check language
Re-run OCR with correct language
If still gibberish, try re-extracting SUB/IDX from disc (files may be corrupted)

💡 Pro Tip: Test with first subtitle

Many OCR tools show a preview of the first subtitle. If the preview is gibberish, STOP and fix the language selection before processing the entire file.

How long does OCR conversion take?

OCR processing time depends on subtitle length, image count, and language complexity:

Typical Processing Times:

TV Episode (22 minutes): 1-3 minutes
TV Episode (45 minutes): 2-5 minutes
Feature Film (90 minutes): 5-8 minutes
Feature Film (120 minutes): 8-12 minutes
Long Film (150+ minutes): 12-20 minutes

Factors affecting processing time:

Number of subtitles: Dialogue-heavy movies take longer
Image resolution: Blu-ray HD subtitles take 2-3x longer than DVD SD
Language complexity: Asian languages (CJK) take longer than Latin scripts
Server load: Processing may be queued during peak usage

⏱️ Patience Required!

OCR is computationally intensive. Do NOT close the browser window or refresh the page during processing, or you'll lose progress and have to start over.

Can I convert multiple subtitle languages at once?

No, you must convert each language track separately. Each language needs its own SUB/IDX or SUP file and appropriate OCR language setting.

Why separate conversion is required:

Each language track is a separate set of files (e.g., movie_eng.sub, movie_spa.sub, movie_fre.sub)
OCR engines are trained for specific languages and cannot process mixed languages
Different languages may have different timing or subtitle counts

🔄 Workflow for Multi-Language DVDs:

Extract all subtitle tracks from DVD/Blu-ray (you'll get multiple SUB/IDX or SUP files)
Identify which file corresponds to which language (check filenames)
Convert each track separately:
- Upload movie_eng.sub/idx → Select English → Get movie_eng.srt
- Upload movie_spa.sub/idx → Select Spanish → Get movie_spa.srt
- Upload movie_fre.sub/idx → Select French → Get movie_fre.srt

What if OCR misses some characters?

Missing or incorrect characters are normal in OCR output and must be fixed manually.

Common OCR Character Errors:

Frequently Confused Characters:

I ↔ l ↔ 1 (capital i, lowercase L, number 1)
O ↔ 0 (letter O vs zero)
rn → m (r+n looks like m)
vv → w
cl → d
nn → m

Often Missed Characters:

Periods (.) at end of sentences
Commas (,)
Apostrophes (') → becomes empty space
Quotation marks (")
Hyphens (-) in compound words

How to fix efficiently:

Watch video with OCR subtitles: This is the fastest way to spot errors
Note errors as you watch: Keep a list of timestamp + error
Edit SRT file: Open in text editor (Notepad++, VS Code) and fix mistakes
Use Find & Replace carefully: Fix repeated errors (e.g., name spelled wrong throughout)

💡 Reality check: Even professional subtitle services manually proofread OCR output. Budget 30-60 minutes for proofreading a 2-hour movie.