Hmm... hard to say what it could be... again, try changing the video driver to GLES 3.0.
If you are still experiencing those black bars for Mario 64, then change the "resolution" setting to NATIVE (highest). That may do the trick.
If it does NOT do the trick, let us know... I'm sure we'll somehow figure it out. Also, I'll make a short video to show you how it runs on mine so maybe you can figure out what is causing it, etc.