Convert SUB/IDX to SRT

Convert DVD SUB/IDX Subtitles to Editable SRT Format

Convert image-based SUB/IDX (VobSub) subtitles from DVDs and video files to editable SRT text format using advanced OCR technology. Extract subtitles from DVD rips, convert VobSub to SRT, and edit subtitle timing or text freely. Supports multiple languages with automatic detection.

What are SUB/IDX Subtitles?

SUB/IDX, also called VobSub format, is an image-based subtitle format commonly found on DVDs and in DVD rips. Unlike text-based formats like SRT, SUB/IDX subtitles store each subtitle line as a bitmap image. This format always comes as two files:

• .sub file - The large file containing actual subtitle images (bitmaps of text rendered in specific fonts and colors)
• .idx file - The small index file with timing information, language codes, and pointers to subtitle images in the .sub file

Because SUB/IDX subtitles are images, you cannot edit the text, change fonts, or modify timing easily. Converting to SRT format using OCR creates editable text subtitles that work with all media players and subtitle editors.

Why Convert SUB/IDX to SRT?

Make Subtitles Editable

Image-based SUB/IDX subtitles cannot be edited without specialized software. After converting to SRT, you can edit subtitle text in any text editor (Notepad, VS Code, Sublime) to fix typos, improve translations, or change wording. Essential for subtitle creators and translators.

Adjust Subtitle Timing Easily

Once in SRT format, you can use subtitle timing tools like our Subtitle Shifter to sync subtitles perfectly with your video. SUB/IDX files require specialized tools to adjust timing. SRT files are simple text files you can shift, split, or merge with any subtitle editor.

Reduce File Size Dramatically

SUB files containing subtitle images can be 5-20MB or larger, especially for movies with complex fonts or colored subtitles. Converted SRT text files are typically 50-200KB—a reduction of 98-99%. Much easier to store, share, and transfer.

Universal Compatibility

While most media players support SUB/IDX, SRT format has even wider compatibility. SRT works on smartphones, tablets, smart TVs, web players, video editing software, and subtitle editors. Converting to SRT ensures your subtitles work everywhere.

Extract Multiple Language Tracks

DVD subtitles often contain multiple language tracks in a single SUB/IDX file pair. Our tool detects and extracts all language tracks, giving you separate SRT files for each language (English, Spanish, French, etc.). Perfect when you need only specific languages or want to distribute subtitles separately.

Common Use Cases

1. DVD Rips and Personal Video Collections

You've ripped your DVD collection to digital video files (MKV, MP4, AVI). The extracted subtitle files are SUB/IDX format. Convert them to SRT so you can easily edit them, sync them if needed, and reduce file sizes for your media server (Plex, Jellyfin, Emby).

2. Fixing OCR Errors from DVD Subtitles

DVD subtitles often have OCR errors ("rn" recognized as "m", "l" as "I") that you need to fix. Convert SUB/IDX to SRT, then open the SRT file in a text editor and correct mistakes manually. Much faster than trying to fix image-based subtitles.

3. Creating Custom Subtitles from DVDs

You want to extract English subtitles from a DVD, translate them to another language, or adapt them for a different video cut. Convert SUB/IDX to SRT to get editable text, then translate or modify the subtitles using subtitle editors like Subtitle Edit or Aegisub.

4. Extracting Forced Subtitles from DVDs

Many DVDs have "forced" subtitle tracks that only show subtitles for foreign language dialogue. These are often embedded as SUB/IDX. Extract and convert them to SRT so you can merge them with full subtitle files or use them standalone for bilingual videos.

How to Extract SUB/IDX Files from DVDs

Before you can convert SUB/IDX to SRT, you need to extract the subtitle files from your DVD or video file:

From DVD Discs (MakeMKV Method)

1. Download and install MakeMKV - Free DVD/Blu-ray ripping software (free while in beta)
2. Insert DVD and open MakeMKV - It will scan the disc and show all video tracks
3. Select subtitle tracks - In the track list, check the subtitle tracks you want (marked as "VobSub")
4. Choose output format - Select "Extract to separate files" for subtitles
5. Start extraction - MakeMKV will create .sub and .idx files for each selected language

From MKV Video Files (MKVToolNix Method)

1. Download and install MKVToolNix - Free MKV editing suite
2. Open MKVToolNix GUI - Launch mkvtoolnix-gui (or mkvmerge GUI)
3. Load your MKV file - Drag and drop your video file into the interface
4. Select subtitle tracks only - Uncheck video and audio tracks, keep only subtitle tracks checked
5. Set output filename - Choose where to save the extracted subtitles
6. Start extraction - Click "Start multiplexing" to extract .sub and .idx files

Understanding OCR Accuracy

OCR (Optical Character Recognition) converts subtitle images to text by analyzing pixel patterns. OCR accuracy depends on several factors:

Factors Affecting OCR Quality

• Font complexity - Simple, clean fonts (Arial, Helvetica) have better recognition than decorative or script fonts
• Font size - Larger subtitle text is easier to recognize accurately than small text
• Image quality - High-resolution subtitle images from DVDs give better results than low-quality sources
• Language - Common languages (English, Spanish, French, German) have better OCR support than less common languages
• Special characters - Accented characters (é, ñ, ü) and punctuation may have lower accuracy than standard letters
• Colors and effects - Colored text, outlines, or shadows can reduce OCR accuracy

Common OCR Errors to Watch For

• Character confusion: "rn" recognized as "m", lowercase "l" as uppercase "I", "0" (zero) as "O" (letter)
• Missing punctuation: Commas, periods, and apostrophes may be missed or misplaced
• Word spacing: Occasional missing or extra spaces between words
• Line breaks: Multi-line subtitles may have incorrect line break positions
• Special characters: Accented letters (é becomes e, ñ becomes n) or symbols replaced with similar characters

After conversion, always review your SRT file and manually correct OCR errors. Most conversions achieve 95-98% accuracy, requiring only minor edits.

Multiple Language Support

DVD subtitles often include multiple language tracks in a single SUB/IDX file pair. Our tool automatically:

• Detects all language tracks - Reads the .idx file to identify all available subtitle languages
• Processes each language separately - Runs OCR on each language track using appropriate language models
• Creates individual SRT files - Generates separate SRT files for each language (English.srt, Spanish.srt, French.srt, etc.)
• Provides ZIP download - If multiple languages detected, you can download all SRT files as a ZIP archive or individually

Language detection is automatic based on the language codes stored in the .idx file. Common DVD language codes include: en (English), es (Spanish), fr (French), de (German), it (Italian), pt (Portuguese), ja (Japanese), zh (Chinese), and many more.

Tips for Best OCR Results

• Use high-quality DVD sources - Original DVDs produce better subtitle images than compressed or low-quality copies
• Extract subtitles properly - Use MakeMKV or MKVToolNix to ensure .sub and .idx files are correctly extracted
• Keep both files together - Store .sub and .idx files in the same folder with matching base names (e.g., "Movie.sub" and "Movie.idx")
• Verify language selection - If the .idx contains multiple languages, note which language corresponds to which track number
• Proofread the output - Always review converted SRT files for OCR errors and manually correct them in a text editor
• Save original SUB/IDX files - Keep the original image-based subtitles as backup in case you need to re-convert with different settings

Troubleshooting Common Issues

Issue 1: "IDX file required" Error

Cause: You uploaded only the .sub file without the corresponding .idx file, or the files don't have matching names.

Solution: SUB/IDX format always requires both files. Locate the matching .idx file (it should have the same base name as your .sub file). Upload both files together. If you truly don't have an .idx file, your .sub file might be a different format entirely (MicroDVD text subtitle), in which case try our general subtitle converter instead.

Issue 2: OCR Output is Gibberish or Wrong Language

Cause: The OCR engine selected the wrong language model, or the subtitle images are corrupted/unreadable.

Solution: Check the .idx file language code. If it's incorrect, the OCR may use the wrong language dictionary. Try re-extracting your SUB/IDX files from the original DVD with MakeMKV, ensuring you select the correct subtitle track. If the subtitle images are damaged, OCR cannot recover readable text—you may need a different copy of the subtitles.

Issue 3: Many OCR Errors in the Output SRT

Cause: Poor quality subtitle images, complex decorative fonts, or small text size leading to reduced OCR accuracy.

Solution: Unfortunately, OCR accuracy is limited by the quality of the source images. After conversion, manually proofread and correct errors in the SRT file using any text editor. Common corrections: "rn" → "m", "l" → "I", "0" → "O". For subtitles with extensive errors, consider searching for existing SRT subtitles online rather than converting from SUB/IDX.

What If I Don't Have an IDX File?

If you only have a .sub file without a matching .idx file:

• Check if it's really VobSub: VobSub SUB files are binary image files (large, 5-20MB). If your .sub file is small (under 1MB) and opens as readable text, it's probably MicroDVD text format instead.
• For MicroDVD .sub files: Try our general SRT converter, which handles text-based .sub files
• For real VobSub without IDX: Unfortunately, conversion is impossible without the .idx file. The .idx file contains essential timing and language data that cannot be recovered from the .sub file alone. You'll need to re-extract from the original DVD or find a complete SUB/IDX pair.

Related Tools

• Convert SUP to SRT - Convert Blu-ray PGS (SUP) image-based subtitles to SRT format
• Subtitle Shifter - Sync your converted SRT subtitles with video timing
• UTF-8 Converter - Fix encoding issues in converted SRT files (for non-English languages)
• SRT Cleaner - Remove formatting artifacts from OCR-converted subtitles
• All Subtitle Tools - Browse our complete collection of subtitle editing tools

Frequently Asked Questions

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

Both are image-based subtitle formats. SUB/IDX (VobSub) is used on DVDs and comes as two files (.sub + .idx). SUP (PGS) is used on Blu-ray discs and comes as a single .sup file. Both require OCR to convert to text-based SRT format. Use our SUP to SRT converter for Blu-ray subtitles.

Why is my SUB file so large (10-20MB)?

SUB files store every subtitle line as a bitmap image. A 2-hour movie may have 800-1500 subtitle images stored in the .sub file, resulting in large file sizes. After converting to SRT text format, file size typically reduces to 50-200KB (a 99% reduction), as text is much more storage-efficient than images.

Can I edit SUB/IDX subtitles directly without converting?

Technically yes, but it's extremely difficult. You would need specialized software like SubtitleCreator or SUBtool to edit individual subtitle images pixel-by-pixel—essentially creating new subtitle images from scratch. Converting to SRT and editing the text is 100x easier and faster for any text corrections, timing adjustments, or translation work.

How accurate is the OCR conversion?

OCR accuracy for DVD subtitles is typically 95-98% for clean, high-quality subtitle images in common languages (English, Spanish, French, German). Expect some minor errors like "rn" recognized as "m" or "l" as "I" that require manual correction. Complex fonts, small text, or less common languages may have lower accuracy (85-90%). Always proofread your converted SRT file after OCR processing.

Do I get all languages if the DVD has multiple subtitle tracks?

Yes! If your SUB/IDX file pair contains multiple language tracks (common on international DVDs), our tool will detect and process all languages automatically. You'll receive separate SRT files for each language track (English.srt, Spanish.srt, French.srt, etc.), or a ZIP archive if there are multiple languages. Check the results page after upload to download individual languages or all at once.