Report MIME type / file extension mismatch as an informative message

[Sombrero51]

EpubCheck 4.2.2 did not detect an error in the .opf file that concerned an audio resource declared with an incorrect media-type.

Incorrect but not detected by EpubCheck 4.2.2:

<item id="audio-internal" href="audio/audio.mp3" media-type="audio/mp4" fallback="fallback" />

Fixed:

<item id="audio-internal" href="audio/audio.mp3" media-type="audio/mpeg" fallback="fallback" />

I noticed the error with the Calibre Check Book, integrated in the e-book editor.

(edited by @rdeltour to add code formatting blocks)

[rdeltour]

Thanks for the report!

I understand that you expected EPUBCheck to detect the mismatch between the declared media type (audio/mp4) and the file extension (.mp3). Correct?

EPUBCheck currently does not base its checks on file extensions. It is not disallowed —i.e. conforming to the specs— for an actual MP4 file to have a .mp3 extension (even if it would be confusing and probably pretty rare).

I guess EPUBCheck could report this as an informative message (not an error or warning); but I think it’s all it could do…

[Sombrero51]

Yes It is correct.

Yes, maybe it could be useful if it reported it as an informational message. But it's my opinion.

Thanks for the clarification!