Frame rate can also be fps or frames per second. Frame bitrate can be bits/s or bits per second. The more frame per second the less bits per frame you'll get if you don't change the bitrate, and the number of bits per frame essentially determines the quality. A frame has a number of pixels, the height times the width of the frame, and the higher your resolution the higher the number of pixels. So, if we still stick to our given bitrate, if you increase the resolution you get less bits per pixel which again means less quality.