MED_011 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.

EPUBCheck · Images, audio and media overlays

EPUBCheck MED_011: chapter in two media overlays

Updated: Nov 4, 2026

EPUBCheck MED_011 is an error message: “EPUB Content Document referenced from multiple Media Overlay Documents.” A content document is referenced from more than one media overlay. The media-overlay attribute names a single SMIL file per chapter, so the narration of one chapter has to be in one overlay.

The official message

EPUB Content Document referenced from multiple Media Overlay Documents.

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

Two SMIL files that both point to the same chapter, for example after splitting the narration.
A chapter split or merged after the overlays were generated.

How to fix it

Find which SMIL files reference the chapter EPUBCheck names (their text elements' src attributes).
Merge the narration of that chapter into one SMIL file, or split the chapter so each overlay narrates its own document.
Make the media-overlay attribute of the chapter's manifest item name the remaining overlay.
Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

When it's not this

If only the media-overlay attribute names the wrong overlay, the error is MED_012.

Terms used here

Other MED messages

MED_010 EPUB Content Documents referenced from a Media Overlay must specify the "media-overlay" attribute.
MED_012 The "media-overlay" attribute does not match the ID of the Media Overlay that refers to this document.
MED-009 The time specified in the clipBegin attribute must not be the same as clipEnd.
MED_013 Media Overlay Document referenced from the "media-overlay" attribute does not contain a reference to this Content Document.
MED-008 The time specified in the clipBegin attribute must not be after clipEnd.
MED_014 Media overlay audio file URLs must not have a fragment, but found '#…'.

Sources

EPUB 3.3, §9.3.5.1 Including media overlays · read Nov 4, 2026

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