MicroDVD Subtitle (.sub)
MicroDVD StandardMicroDVD Subtitle (SUB) is a legacy frame-based subtitle format that synchronizes dialogue cues using exact video frame numbers rather than absolute clock timestamps.
Convert SUB to SRT
Free in-browser SUB to SRT converter. Convert files instantly on your device.
Inspect & Metadata
Operating systems and file analyzers identify SUB files by inspecting the leading binary byte sequence:
Byte-Level Header Signature (Magic Bytes)
Operating systems and file analyzers identify SUB files by inspecting the leading binary byte sequence:
HEX SIGNATURE (OFFSET 0):
7B 31 7D 7B / 7B 30 7D 7BASCII REPRESENTATION: {1}{ / {0}{
Standardization: MicroDVD File Specification
Technical Specifications
| Container Architecture | Frame-based text format where each line defines {start_frame}{end_frame} followed by subtitle text |
| Compression | Uncompressed plain text |
| Byte Endianness | UTF-8 or ANSI text stream |
| Color Spaces | Optional MicroDVD control codes ({y:b}, {y:i}, {c:$BBGGRR}) |
| Channels & Structure | Frame-synchronized subtitle text with basic formatting |
| Max Dimensions | Unbounded sequential lines |
| Transparency | None |
| Streaming & Progressive | Sequential frame-by-frame streaming playback |
Technical Comparison Matrix: SUB vs Competitors
| Technical Attribute | SUB (Current) | SRT | VTT | ASS |
|---|---|---|---|---|
| Timing Mechanism | Frame numbers ({start_frame}{end_frame}) | Timecodes (HH:MM:SS,mmm) | Timecodes (HH:MM:SS.mmm) | Timecodes (H:MM:SS.cc) |
| Frame Rate Dependence | 100% dependent on exact video FPS | Independent of video frame rate | Independent of video frame rate | Independent of video frame rate |
| Modern Web Support | None (requires conversion) | Requires JS conversion | Native HTML5 <track> | Requires WebAssembly |
| Current Usage | Legacy DivX/XviD archives | Universal global standard | Modern web video standard | Anime & stylized subtitles |
Common Corruption Modes & Hex Recovery Guide
Subtitles play twice as fast or twice as slow as the movie audio.
Root Cause: Frame rate mismatch (e.g. subtitle timed for 29.97 fps video played with 23.976 fps file).
Recovery: Convert to timestamp-based SRT with correct FPS using File2File Subtitle Converter.
Security Analysis & Parser Attack Vectors
MicroDVD parsers evaluate frame calculation mathematics where integer overflow can cause buffer memory corruption.
Known Attack Vectors
- Integer overflow during frame-to-millisecond timestamp conversion.
- Buffer over-read when parsing unclosed curly brace tags.
- Denial of service through negative or descending frame number sequences.
Defensive Best Practices: Validate that end frame numbers are strictly greater than start frame numbers.
Historical Origins & Milestones
Key Advantages & Pros
- Guarantees exact frame-accurate subtitle timing tied directly to video refresh cycles.
- Extremely compact syntax: each cue occupies exactly one line of text (e.g. '{100}{250}Hello world').
- Supported by major legacy desktop media players (VLC, MPC, GOM Player).
Technical Limitations & Cons
- Frame-rate dependent: if the video frame rate changes (e.g. from 23.976 fps to 25 fps), all subtitles immediately lose synchronization.
- Ambiguous file extension: '.sub' is also used for binary VobSub DVD bitmap graphics.
- Not supported natively by modern web browsers or streaming platforms.
Interesting Technical Trivia
- Each line in a MicroDVD SUB file starts with curly braces containing frame numbers: '{1200}{1280}Watch out!'.
- If a SUB file does not declare the video frame rate on line 1, modern media players must guess the frame rate (often causing sync errors).
- The format was created specifically for the classic MicroDVD Player, which allowed custom skins on Windows 98.
Frequently Asked Technical Questions
Why are my .sub subtitles out of sync with my video?
Because .sub files use frame numbers instead of real time. If your video is playing at a different frame rate (like 24 fps vs 30 fps) than the subtitle was created for, it will drift out of sync.
How can I convert .sub to .srt?
You can convert frame-based .sub files into universal, timecoded .srt subtitles in one click using File2File.app directly in your web browser.
What is the difference between text .sub and VobSub .sub?
Text .sub (MicroDVD) is a plain text file with curly braces. VobSub .sub is a binary file containing raw graphical images ripped directly from a DVD, paired with an .idx index file.