Some people get confused about this because they count from zero and include ones (darned programmers ;~). 4 fps means you'd get images taken at time 0, 0.25, 0.5, and 0.75 seconds (and another at 1s, which is why some people erroneously think 4 fps is 5 fps, but 1 is the start of the second second). A better way of thinking of it is what is the average number of frames you get in any given second out of a much longer period of time. At 4 fps, the answer would be 4.
With video, you get a completely unexpected answer. 30 fps is not actually 30 fps, but rather 29.97 fps. What? Long story, but it has to do with the way television frequencies were calculated. 30 fps is a rounded number from what was actually used. Same is true of the other video frame speeds, too, except in PAL countries.