Most songs available on Tracklib include the right to synchronize the new song (derivative work) containing a sample. However, tracks marked with ‘Sync on Request’ do not include the rights to synchronization of the derivative work without prior approval of the original rightsholders. This means that when you purchase a license for these songs, the original rightsholders (original label/artist and/or publisher/songwriter) have to be contacted to provide their approval if you are to synchronize your new song to any form of TV/video/podcast/advertisement or similar. These approvals are usually handled by the sync licensee, that is the company/individual who wants to synchronize your song, who needs to contact the original rightsholders directly.