Try this, if not already have:
Press and hold Side key until you see Power Off - select it to power off the phone.
Now, off to the Maintenance (Recovery) screen:
Press and HOLD the Volume Up key, and while holding, press and HOLD the Side key.
When the Samsung splash screen appears, release both keys. Within a few seconds, you'll see the Maintenance screen, with a number of menu options.
Use the Volume Down key to highlight Wipe Cache Partition. Press Side key, select "Yes".
Now, Use Volume key to highlight "Repair Apps" (should be last menu option). Use Side key to select it.
The phone will automagically restart. Let the phone settle down for a couple of minutes.
... retry videos ...
I am very sorry to hear about videos freezing while playing, and can understand how incredibly frustration it is. Have you tried operating in Safe Mode and seeing if videos on the stock app(s) play properly? A third party application might be to blame, so try this guide out: https://www.samsung.com/us/support/answer/ANS00062983/
Also, you can try clearing your device's cache partition. The steps are:
• Ensure the device is powered off. If the device is unresponsive/frozen, press and hold the Power button for approximately 10 seconds or until the device power cycles.
• Press and hold the Volume Up button and the Home button.
• While continuing to hold the Home and Volume Up buttons, press and hold the Power button until 'RECOVERY BOOTING' appears in the upper left then release all buttons.
• Select wipe cache partition. Utilize the Volume Up/Down buttons to highlight and the Power button to select.
• Select reboot system now. Option is highlighted, utilize the Power button to select.
Finally, you can try clearing the cache on the apps in question and seeing if that helps. The steps for that are here: https://www.samsung.com/us/support/answer/ANS00077611/
Please let me know if this helps.