Video and sound of video stops after a few seconds

Hi n4nnor,

Welcome to Apple Support Communities. I understand you're having trouble with videos pausing while you're using Snapchat and Twitter, but other apps and video playback is unaffected. I can see why you'd reach out about this behavior; I'd like to help. Although the apps seem to be functioning properly outside of the video issue you're seeing, I'd recommend following the steps below for each affected app:

"Force quit the app

• • iPhone, iPad, iPod touch: Close the app and open it again.

Restart your device

Restart your iOS device, Apple Watch, or Apple TV. Then open the app to see if it works as expected.

Check for updates

Make sure that your device has the latest version of iOS, watchOS, or tvOS.

Then check for app updates. For iOS and Apple Watch apps, go to the App Store on your iOS device, then tap Updates. If an update is available, tap Update. If asked, enter your Apple ID and password. You might need a Wi-Fi connection to update some apps on your iOS device.

Delete and reinstall the app

• • iPhone, iPad, iPod touch: Delete the app, then redownload it from the App Store.
  • Apple TV: Highlight the app on the Home screen, then press and hold the Touch surface until the app jiggles. Press Play/Pause, then select Delete. Open the App Store and redownload the app. Some apps require subscriptions for activation. If you can't activate the app or you don’t remember your sign-in information, contact the app developer.
  • Apple Watch: Open the Watch app on your iPhone and tap the My Watch tab. Scroll to the app you want to remove, then tap it. Turn off Show App on Apple Watch, and wait for it to disappear from your watch's Home screen. To reinstall the app, scroll down to Available Apps in the My Watch tab and tap Install.

Contact the app developer 

If you're having an issue with an Apple app, contact Apple Support. If it's a third-party app, contact the app developer."

If an app unexpectedly quits, stops responding, or won’t open

Best Regards.