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EPUBCheck · Images, audio and media overlays

EPUBCheck MED_010: no media-overlay attribute

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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.

The official message

EPUB Content Documents referenced from a Media Overlay must specify the "media-overlay" attribute.

Default severity
Error. The EPUB breaks a rule of the specification and is invalid. Stores and Send to Kindle may reject it, and EPUBCheck exits with status 1.
EPUBCheck version
5.4.0

EPUBCheck prints this ID with an underscore instead of a hyphen; this page uses the ID exactly as EPUBCheck reports it.

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.

Terms used here

Other MED messages

  • MED-009 The time specified in the clipBegin attribute must not be the same as clipEnd.
  • MED_011 EPUB Content Document referenced from multiple Media Overlay Documents.
  • MED-008 The time specified in the clipBegin attribute must not be after clipEnd.
  • MED_012 The "media-overlay" attribute does not match the ID of the Media Overlay that refers to this document.
  • MED_007 Picture "source" elements must define a "type" attribute when they reference foreign resources; found resource "…" of type "…".
  • MED_013 Media Overlay Document referenced from the "media-overlay" attribute does not contain a reference to this Content Document.

Sources

Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EpubCC.

FAQ

What does EPUBCheck MED_010 mean?

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.

Is MED_010 an error?

MED_010 is reported as error by default. The EPUB breaks a rule of the specification and is invalid. Stores and Send to Kindle may reject it, and EPUBCheck exits with status 1.