Does the issue only occur when you're playing videos you've recorded?

Have you done the following  troubleshooting as outlined in this article yet?

https://support.apple.com/en-us/HT203794

Thanks!

https://support.apple.com/en-us/HT204321

Also you may wan to check in your list of Messages...does any Message have the MOON next to that Contact? Click on that Message, click on Details, and you will see that you have Do Not Disturb on for THAT specific Contact.....You may have Do not Disturb feature enabled for some Contacts and not others....,

Yea don't even read what I said about the Do not Disturb feature because it has no relevance......

Thanks and good luck!