Here's a quick script that works for me to view the output of JeVois with OpenCV. I tried using cam.set(...) to change the size and fps to get a different demo, but so far it only works for the intro, or whatever ends up mapped to the default. However, it will continue running if a separate program is run, so you can actually use ffplay or guvcview to set the resolution after starting the OpenCV viewer to select the program you want. You might have to remove the frame flipping after this.
(This was made for Python 3 and OpenCV 3.0)
This is the only way I've found to view output on macOS without a large delay.
(I didn't see a way to format it as code or attach a file, so here it is...)
from time import sleep
cam = cv2.VideoCapture(1) # Number selects camera, can also use file
while cv2.waitKey(1) != 27: # Break on ESC press
success, frame = cam.read()
cv2.imshow("Webcam", frame[:,::-1]) # Reverse left-to-right
sleep(.1) # Prevent segfaults