Next slap on an ND filter that gives you proper exposure EV=0 while at ISO 100. Most likely this will be an ND8 or ND16 filter. Now you have solved your second problem.
Next go through and shoot short 30 second clips trying out the various modes like D-Cinema, ART etc. No need to try them all, some will look terrible when you look at them on your phones screen. As you record each clip make a notation on paper of the order that you filmed each one and the settings used. You can repeat the mode settings again using +1 and -1 for the sharpness. The whole process took me about 1 hour while sitting in a chair sipping a beer.
Here's how ND filters work with "normal" phtography. I confess I don't get why the ND filter are so high with drones...
Here's why:
The best explanation given for using them is that the longer shutter speed removes the stripes caused by the rotor blades.
The general rule that works for ALL cameras is the "Sunny 16" rule which states that to take a perfectly exposed picture on a sunny day set the aperture to f16 and the shutter speed to 1/ISO. So if you're shooting at ISO 400 pick the shutter speed closest which would be 1/500 or possibly 1/320 if your camera can do 1/2 or 1/3 stop increments.
An ND 8 filter reduces the exposure by 8 stops - which is either an f stop or shutter speed.
Now you want to keep your ISO low as possible to reduce noise. Set it at 100 for best image quality.
So the Mavic has one really dumb design decision -
the lens is a fixed f2.8. This is 4 stops down from f16 (f/2.8, f/4, f/5.6, f/8, f/11, f/16) , This means you're letting in 4 times as much light - to get a correct exposure with the Mavic the shutter speed is increased by that same 4 stops which at ISO 100 is 1/100, 1/200, 1/400, 1/800,
1/1600. That's pretty dang fast and will freeze action and show the stripes.
Adding the ND8 reduces the light by 8 stops. So at ISO 100 this results in a shutter speed of -4 from the base ISO of 100 so the new shutter speed with the ND8 would be 1/100, 1/50, 1/25, 1/12. This shutter speed is slow enough to turn waterfalls into cotton candy. Nice if you want to get artsy fartsy but 1/60th is actually likely where we'd like to be - so to speed it back up we need to bump the ISO by two stops so now we're ISO 200,
400. Not too bad as far as noise goes.
But an
ND 16 would add another 8 stops into the mix meaning either a really slow shutter and a really fast ISO. If you balanced you'd have to give 3 to ISO making it ISO 3200 (800, 1600, 3200 [max]) and -5 to the shutter for 1/50, 1/25, 1/12, 1/6, 1/3, 1 second. This just doesn't seem rational making me think I'm missing something.
Anyway - **** shame they didn't provide an aperture with the Mavic.