When you're running a multibitrate stream, it's become customary to use adaptive bitrate (ABR) to have the player automatically play the best stream possible. However, this can conflict with another priority, which is to try not to waste bandwith for mobile users who have a limited amount. How to balance between quality and bandwith savings is a complicated topic, but one thing we can say for sure is that playing a stream with a frame size larger than the phone's screen is a waste of everyone's bits.
To aid in the effort against wasted bits, we offer a setting in our embed generator to limit the bitrate that the player will select to prevent it from exceeding the screen size. Just check the "Limit stream resolution to player size" box in the embed generator, and the generated player will automatically limit itself to the size of the player, whatever that may be.