Kdenlive/Manual/Project Menu/Online Resources
Online Resources
Available from the Project menu and the Add Clip dropdown, this feature allows you to search online audio, video and graphics libraries for resources to download.
Freesound Audio Archive
The freesound audio library part of this became non-functional on old versions of Kdenlive in Oct 2015 because freesound now requires user registration. If you are using and old version of Kdenlive you can still download great audio clips from https://www.freesound.org/ - just not through the Kdenlive interface.
Version 15.? Dec 2015 allowed users to automatically download the high quality .mp3 preview file from freesound using the Online Resources module.
Freesound Audio Archive - Future version
A future version of Kdenlive will allow you to authenticate kdenlive with your free freesound web account and download the high quality files.
If the Online Resources dialog offers up this error
Error Getting Access Token from Freesound. Try importing again to obtain a new freesound connection
Hit the import button again to make it try and establish a new authentication handshake with the free sound web site.
Revoke kdenlive's access to your freesound account from the freesound web site. Log in to your account and click the link in the App permissions section on the settings page "Manage your list of permissions granted to API applications" http://freesound.org/home/app_permissions/