Some criteria that qualify as public domain are:
When getting copyright permission you need to get both the publishing and the recording rights. The publisher owns the right to lyrics and composition; this is known as the synchronization license. The record label owns the rights to the recording; this is known as the master use license. Be aware that if there are several versions of the song you will need to find which record label owns the rights to the version you are using. You may want to get permission from the publisher first, because when you approach the record label you can fax them copy and it usually opens the door for you.
When trying to obtain permission you might want to consider the following:
Eligibility:
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