Sergey Biryukov

Recent minor updates for WordPress introduced a couple of regressions when uploading audio and video files:
<ul>
<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.

Peter Westwood

This plugin allows you to configure extra mime-types for support by the inline-uploader.
A new options page is added as Options … Mime-types which allows you to add/delete the extra mime-types.
By default the following extra mime-types are registered: audio/ac3, audio/MPA and video/x-flv.
With version 0.90 of the plugin you are now able to upload a file containing a long list of mime types as an easy way to register multiple mime-types. 
The file format is “mime/type extension” for example like this:
<pre><code>audio/ac3 ac3
audio/MPA mpa
video/x-flv flv
</code></pre>

PJW Mime Config

This plugin allows you to configure extra mime-types for support by the inline-uploader.

Correct Audio/Video Uploads vs PJW Mime Config