The rotation lock feature on any iOS device can be extraordinarily useful, except when it’s not. More specifically, it tends to be less convenient when you watch videos because it tries to display the (usually widescreen) video in portrait orientation on your tall-displayed device, resulting in something like what you see above on the left.
Fortunately, those with jailbroken handsets can now spearhead this problem dead-on with a new free jailbreak tweak called Video Direction Control (iOS 11) by iOS developer rf00.