ms-files.php sets *.webm mimetype incorrectly

[braydonf]

The content-type of *.webm files is incorrectly being set to image/webm by ms-files.php for multisite networks on uploaded *.webm videos in the media library.

There is no reference to .webm in core... so you must be filtering the list of allowed file extensions/MIME types in order to be able to upload WebM videos in the first place?

In one of the themes I have done so yes, using this in functions.php

    add_filter( 'upload_mimes', 'custom_mimes' );

    function custom_mimes( $mimes ){
        $mimes['webm'] = 'video/webm';

        return $mimes;
    }

However in the rewrite to wp-includes/ms-files.php, the filter isn't being run since it is "outside" of a site.

The rewrite is also preventing some aspects of the video to be displayed correctly, since it's not being served directly from Apache. This is part of a larger issue.

Ah, I see the problem now.

Related: #14659

Patch attached to #14659