I allowed upload of "any" type via LocalFiles Editor plugin:

   $conf['upload_form_all_types'] = true;

This option adds more filetypes including .mp4 files.
This worked for me.

Thanks for posting the solution.  I tried many things before checking the forum.

Albert, your site URL must be mispelled, the way you posted it, it cannot be reached.

Have you 'synced' the uploaded files with VideoJS after the upload?
The sync option updates the database and prepare video thumbnails.