Hey there marcoj715,
Thanks for reaching out to the Apple Support Communities. To get started, do you by chance have your photos and videos synced with iCloud? If unsure, you can check this by going into Settings > [Your Name] > iCloud, and see if 'Photos' has been enabled.
If iCloud Photos are enabled, are you able to play the videos as expected if you log into your iCloud account (from a computer or iPad) at this link here: iCloud - Apple
If you're able to view the videos as expected at the link above, try testing the issue on another Wi-Fi network. This can help rule out a possible network issue causing the videos not to play as expected.
Let us know what you find.
Take care!