Hey there susanjtyler,
Thanks for contacting the Apple Support Communities today!
To get started, have you had a chance to look over your notification settings to ensure that everything is set up correctly? If not, take a look at the steps in the following resource that can help with that: Use notifications on your iPhone or iPad - Apple Support
Change alert styles
1. Go to Settings and tap Notifications.
2. Select an app under Notification Style.
3. Under Alerts, choose the alert style that you want. If you turn on Allow Notifications, choose when you want the notifications delivered—immediately or in the scheduled notification summary.
With iOS 15 and iPadOS 15 or later, you can turn on Critical Alerts for supported apps so notifications come through even if your iPhone is muted or you have a Focus set up.
Since you stated that this is occurring when you have a video or music playing, are you also actively using your iPhone at that time? If so, do you by chance have Attention Aware Features enabled in Settings > Face ID & Passcode? We ask because when Attention Aware Features are enabled, your notification volume will lower considerably when looking at your device.
Check out this link for more details, and keep us updated on what you find: Turn Attention Aware features on or off on your iPhone or iPad Pro - Apple Support
Take care.