# EPUBCheck MED_010: no media-overlay attribute, how to fix it

Source: https://epubcc.com/epubcheck/med_010/ (updated 2026-11-04)

EPUBCheck MED_010 is an error message: “EPUB Content Documents referenced from a Media Overlay must specify the "media-overlay" attribute.” A content document is used by a media overlay, but its manifest item has no media-overlay attribute. The attribute is how the reading app finds the narration for a chapter, so without it the audio is never played.

- Official message (EPUBCheck 5.4.0): EPUB Content Documents referenced from a Media Overlay must specify the "media-overlay" attribute.
- Default severity: Error

## Typical causes

- A SMIL file added to the book without updating the manifest item of the chapter it narrates.
- A manifest regenerated by a tool that dropped the attribute.

## How to fix it

1. In the package document, find the manifest item of the chapter EPUBCheck names.
2. Add media-overlay="..." with the id of the manifest item of its SMIL file, for example <item id="ch1" href="ch1.xhtml" media-type="application/xhtml+xml" media-overlay="ch1_audio"/>.
3. Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

## When it's not this

If the attribute is there but names a different overlay, the error is MED_012.

## Sources

- EPUB 3.3, §9.3.5.1 Including media overlays: https://www.w3.org/TR/epub-33/#sec-package-including (read 2026-11-04)

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