# EPUBCheck OPF-036: video type may not play, how to fix it

Source: https://epubcc.com/epubcheck/opf-036/ (updated 2026-11-04)

EPUBCheck OPF-036 is a usage message: “Video type "…" might not be supported by reading systems.” A video uses a media type that reading apps may not support. This is a usage note (shown with -u), and EPUBCheck suggests video/mp4, video/h264 or video/webm instead.

- Official message (EPUBCheck 5.4.0): Video type "%1$s" might not be supported by reading systems
- Default severity: Usage
- EPUBCheck's suggestion: Use "video/mp4", "video/h264" or "video/webm" instead.

## Typical causes

- Video exported in a less common container or codec, such as Ogg or QuickTime.
- Video copied from a website in whatever format the site used.
- A manifest media type that does not describe the real file.

## How to fix it

1. Check which formats the reading apps you target can play.
2. Re-encode the video as MP4 (H.264) or WebM if you need it to play widely.
3. Update the manifest item's media-type and the source element's type attribute to the new format.

## When it's not this

If the video is placed directly in the spine, the rules for spine items and fallbacks (OPF-043) apply as well.

## Sources

- EPUB 3.3, §3.2 Core media types: https://www.w3.org/TR/epub-33/#sec-core-media-types (read 2026-11-04)
- EPUB 3.3, §3.3 Foreign resources: https://www.w3.org/TR/epub-33/#sec-foreign-resources (read 2026-11-04)

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EpubCC.