I have always shot video with manual settings. Typically my shutter would be 1/50.
This is a comparison between 'M' and 'A' exposure (video) modes on the Panasonic GH4.
Manual settings using 1/50, ISO200 and f14 for perfect exposure.
AP mode - I dialed in f2.8, ISO200 and let the camera choose the shutter speed. Results were nice shallow depth of field. No lens filters used. I haven't figured out how to determine what shutter speed was used in AP mode though.