Playback window is small, especially on handheld devices. Allow users to set/change default playback window size (small, medium, large).
By “playback window”, do you mean the live stream and event playback video frames?
If so, when the phone is in portrait orientation, the video frame takes up the full width of the device’s screen. It cannot be any larger without cropping or distorting the image ratio.
However, if you turn your device sideways (to landscape orientation), the video will pop out and expand to fill the full screen. Give it a try.