Looks like the video reader bob.io.video.reader does not close the video file when iterating over frames AND the iteration does not finish fully.

For example:

video = bob.io.base.load('testvideo.avi')
# closes the video file properly

for frame in reader('testvideo.avi'):
    pass
# closes the video file properly

for frame in reader('testvideo.avi'):
    break
# the video file is left open!
import gc
gc.collect()
# the video file is still open!