EPUB vs SUB
A detailed comparison of EPUB eBook and MicroDVD Subtitle — file size, quality, compatibility, and which format to choose for your workflow.
Technical Specifications
| Specification | .EPUB | .SUB |
|---|---|---|
| MIME type | application/epub+zip | text/x-microdvd (MicroDVD); image/vnd.dvb.subtitle (VobSub) |
| Extension | .epub | .sub (paired with .idx for VobSub) |
| Container | ZIP archive | — |
| Markup | XHTML 1.1 (EPUB 2); HTML5 (EPUB 3) | — |
| Standards | IDPF/W3C EPUB 2.0.1, 3.0, 3.2, 3.3 | — |
| Variants | — | MicroDVD (text), VobSub (bitmap) |
| Common conversion | — | OCR VobSub → SRT |
Strengths Comparison
.EPUB Strengths
- Open standard — no vendor lock-in, no DRM required.
- Reflowable text — adapts to any screen size, font size, or orientation.
- Rich typography via CSS, embedded fonts, and SVG.
- Accessibility-first: native support for screen readers, adjustable text, and alt-text.
- Universal across every non-Kindle ebook reader and library app.
.SUB Strengths
- VobSub preserves DVD subtitle appearance exactly.
- MicroDVD is trivially editable text.
- Universal player support (VLC, mpv, MPC).
- Historical format for DVD-era subtitle preservation.
Limitations
.EPUB — Limitations
- Kindle does not support EPUB natively (Amazon wants you to convert to AZW3).
- Fixed-layout EPUBs (for children's books, comics) are awkward to author.
- Rendering quality varies between apps — some CSS works everywhere, some does not.
- Adobe DRM (ADEPT) or Apple FairPlay are optional layers that complicate portability.
.SUB — Limitations
- Bitmap subtitles (VobSub) cannot be edited as text.
- MicroDVD frame-based timing breaks on framerate changes.
- Two incompatible formats sharing one extension causes confusion.
- Superseded by SRT and ASS for editing and modern streaming.
Frequently Asked Questions
EPUB (Electronic Publication) is the open standard eBook format maintained by the W3C. It supports reflowable text that adapts to screen size, embedded fonts, images, and interactive content, making it the most widely supported eBook format globally.
SUB (MicroDVD Subtitle) is a document format used to store paginated text, with optional formatting, tables, images, hyperlinks, headers and footers. It sits in the documents & text family and is typically associated with a specific office suite or publishing pipeline that defined the format and ships the canonical reader.
EPUB files open in Apple Books, Google Play Books, Calibre (free), Kobo eReaders, and Adobe Digital Editions. Note that Amazon Kindle does not natively support EPUB, so conversion to MOBI or AZW3 is needed.
Modern office suites — Microsoft Word, Google Docs, LibreOffice Writer, Apple Pages — open most SUB files with reasonable fidelity. If your installed software does not support SUB, convert to DOCX or PDF first using KaijuConverter; both open in virtually every reader, including free online viewers.
Use EPUB for reading on phones and eReaders since it reflows text to fit any screen. Use PDF for documents with fixed layouts like textbooks with precise formatting, scanned pages, or documents intended for printing.
Upload the SUB to KaijuConverter and pick DOCX, PDF, ODT, RTF, HTML, Markdown, or plain text. Our pipeline runs LibreOffice headlessly plus pandoc for text formats — the same engines behind professional document pipelines. Styles, tables, images, and hyperlinks survive the conversion intact.
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