Macbook Pro Dock appearing randomly during movies and applications running
One thing you could try is a full reset and restart of the Dock. Note you will need to re-add any non-default icons (i.e. apps) that you've added to the Dock - so you may want to take a screenshot of your Dock as a reminder of what you had there. (Or start afresh and only add things as you actually use them).

To reset and restart the Dock, follow these steps:


Go to Finder
Press and hold the option key down
Now go to the Go menu
Select the Library option to open the User's Library folder. You can let go of the option key now.
Go to the Preferences folder (i.e. within the Library folder)
Find and move the com.apple.dock.plist file to the Trash
Now open Terminal (usually located in Applications > Utilities)
Enter this command killall -KILL Dock
Press enter


This should resolve the issue. As mentioned previously, you will need to re-add non-default apps back to the Dock.