I have a button setup to display a trailer in the skin using the mq7 skin also. Plays all quality fine although I’m using a rpi3.
I’m not using tvtunes for this just using skinning displaying a videowindow in the GUI.
For a quick test can you install the confluence skin. Play a video file then navigate back to the main screen. I think confluence by default displays the video in background of main screen. If doesn’t check in settings for show video in background or something.
See if it stutters there.