Hi Shinnen,
Think of your iPhone 5 like a storyteller that always assumes you’re holding the book sideways—even when you’re not. When you shoot in portrait mode, some apps or devices may read the story wrong and flip it sideways, thinking that’s the proper view. Sadly, there’s no magic setting on the iPhone 5 to fix this automatically. The best way is to always hold the phone in landscape if you want the video to play correctly everywhere. Otherwise, you’ll often need to “straighten the painting” afterward using video editing software. Hope that helps!