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You may not use commercial music for your videos unless you have some form of license (that you pay for) or other permission to use it. The music is the copyrighted property of the composer/producer. I don't know where you got the copyright waiver form, but unless it's signed by the person or company whose work you want to copy, it won't help you.
Speak to a copyright attorney to get your documentation together; that way you'll be able to present your clients with a contract that's fair, accurate and within the bounds of the law.
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