What are the advantages of the SUB format?

Frame-accurate timing that precisely matches video frame boundaries. Simple format that is easy to parse and generate programmatically. Supported by many popular media players including VLC.

What are the limitations of SUB?

Frame-based timing requires knowledge of video frame rate for correct display. Changing the video frame rate misaligns all subtitle timing. Less intuitive than timestamp-based formats for manual editing.

MicroDVD Subtitle (.SUB)

Q: What is the MIME type of SUB?

The official MIME type for SUB files is text/x-sub.

SUB (MicroDVD Subtitle) is a frame-based subtitle format that uses frame numbers rather than timestamps for timing synchronization. Each line contains start and end frame numbers enclosed in curly braces followed by the subtitle text, with pipe characters separating multiple display lines. SUB requires knowing the video frame rate to correctly synchronize subtitle display timing.

.SUBtext/x-subSubtitle Converter

Advantages of MicroDVD Subtitle

What the SUB format does well, and why you might choose it.

Frame-accurate timing that precisely matches video frame boundaries
Simple format that is easy to parse and generate programmatically
Supported by many popular media players including VLC

Limitations of MicroDVD Subtitle

What the SUBformat doesn't do well, and when to choose another format.

Frame-based timing requires knowledge of video frame rate for correct display
Changing the video frame rate misaligns all subtitle timing
Less intuitive than timestamp-based formats for manual editing

What SUB files are used for

Legacy subtitle files for video content
Frame-accurate subtitle synchronization for specific video encodes
Subtitle conversion source for timestamp-based format output

How SUB files work

Subtitle formats carry timed text aligned to a video timeline. SRT (SubRip) is the simplest — start time, end time, text, blank line — and most widely supported. VTT (WebVTT) is the HTML5 standard and supports basic styling, positioning, and chapter cues. ASS/SSA (Advanced SubStation Alpha) supports rich typography, multiple styles, animation, and per-line positioning, and is the format of choice for fansubs and karaoke. Embedded subtitles (in MKV or MP4) carry SRT, VTT, or PGS (image-based) tracks inside the video container itself.

Best practices when working with SUB

Use SRT for maximum compatibility — every video player, streaming platform, and editing tool reads it. Use VTT when delivering web video to HTML5 video elements; it's the format browsers natively understand. Use ASS/SSA when typography and positioning matter (fansubs, karaoke, complex educational content). Validate timecodes after auto-generation: ASR-generated subtitles often have overlapping cues and unrealistic display durations that look wrong on playback. Encode in UTF-8 with BOM if your subtitles include non-Latin characters and you want broad compatibility.

Convert to SUB

The most common formats people convert to SUB, ready to convert in seconds.

SRT → SUB ASS → SUB SSA → SUB VTT → SUB JSON → SUB

Convert SUB to other formats

Convert MicroDVD Subtitle files into the format you actually need.

SUB → SRT SUB → ASS SUB → SSA SUB → VTT SUB → JSON

Choosing SUB versus the alternatives

SRT: distribution to platforms and players that may not support newer formats. The lowest-common-denominator. VTT: HTML5 video, web platforms, modern streaming. SUB and IDX: legacy DVD-style subtitle pairs you'll probably want to convert away from. ASS/SSA: when you need precise positioning, multiple styles, or animation effects.

Where SUB fits in real workflows

Subtitles are usually authored in a dedicated tool (Aegisub for ASS, web tools for SRT/VTT, professional captioning tools for broadcast) and exported to whatever format the destination platform requires. Most conversions are between the three text-based formats (SRT, VTT, ASS); converting from image-based formats (SUB/IDX) requires OCR.

Privacy and file handling

When you convert a SUBfile with MegaConvert, the file is uploaded to our converter, processed, and automatically deleted within an hour. We don't train models on your files, share them with third parties, or retain them after the conversion completes. The download link expires when the file is removed. If your work involves files subject to NDA or compliance requirements (HIPAA, GDPR data processing), please review our privacy policy before uploading sensitive material.

Frequently asked questions about SUB

What is a .SUB file?

What is the MIME type of SUB?

The official MIME type for SUB files is text/x-sub. This is the value web servers and applications use to identify the format when transferring files.

What category does SUB belong to?

SUB is a Subtitle Converter format. Files in this category share common conversion paths and use cases.

How do I open a .SUB file?

SUB files are typically opened by software that natively supports the MicroDVD Subtitleformat. If you don't have a compatible application, the most reliable approach is to convert the file to a more universal format using the converters listed above. Most MicroDVD Subtitle files convert to widely-supported alternatives in seconds.

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Convert SUB to SRT