The file size depends on the variables of the cameras like resolution, compression rate and fps.
Resolution: The higher the resolution, the smaller the file size. The file size of resolution 640x480 is two times larger than that of 640x240, and four times larger than that of 320x240.
Compression rate: The higher the compression rate, the smaller and the less clear the file size is, vice versa.
FPS: FPS refers to frame shown on screen per second. The larger the number of fps, the smoother the image displayed but the larger the file size. Then using 320x240 and medium is selected as compression rate by VioGate, each frame size will be 5~10KB.