Sergey Biryukov

Recent minor updates for WordPress introduced a couple of regressions when uploading audio and video files:
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<li>
On WordPress 4.3.x and earlier branches, audio/video files cannot be uploaded at all due to a fatal error.
Full list of affected versions: 3.7.19, 3.8.19, 3.9.17, 4.0.16, 4.1.16, 4.2.13, 4.3.9.
This will be fixed in the next minor update, see the <a href="https://core.trac.wordpress.org/ticket/40085" rel="nofollow ugc">Trac ticket #40085</a>.
</li>
<li>
On WordPress 4.4.x and later branches, audio/video files are uploaded with corrupted thumbnails.
Full list of affected versions: 4.4.8, 4.5.7, 4.6.4, 4.7.3.
This will be fixed in the next minor update, see the <a href="https://core.trac.wordpress.org/ticket/40075" rel="nofollow ugc">Trac ticket #40075</a>.
</li>
</ul>
In the meantime, this plugin is a workaround that solves both issues and restores the upload functionality for audio and video files.
Don’t forget to remove the plugin once the next minor WordPress update is available!

Correct Audio/Video Uploads

Restores the ability to upload audio & video files in recent minor WordPress updates.

edik

If FacadeX is active, the public WordPress sites are sent with the xhtml mime type. The internal sites like the administration panel and the login screen, which have many xhtml syntax errors, are still sent with the standard mime type.
You must ensure that your public sites have valid XHTML, otherwise you will get parsing errors in your browser.

FacadeX

Sends public sites with the XHTML mime type. The internal sites, which have many XHTML errors, are still sent with the HTML mime type.

Correct Audio/Video Uploads vs FacadeX