I'm definitely a stills shooter (First time Video user), but thought I'd have some fun and try out the video feature on the D4. THIS WAS JUST AN EXERCISE TO LEARN THE CAMERA have a look: http://youtu.be/3av49u1O5NU?hd=1
Impressions of Video Feature:
AUTO FOCUS - Low light Auto focus is non existent. don't even try. You need a fair amount of light for it to work. Once sufficient light, it works well. I think I will be using manual focus though. Face detection worked OK when people were running towards camera. if the camera and subject is fairly static or slow moving (and enough light) it works well.
CROP MODE - 2.7x crop mode is very useful, I shot with 28mm, 50mm, 24mm-70mm. I left the long lens (70mm-200mm) at home to save weight. In low light, I could not notice quality difference between standard, DX, and 2.7x crop. I tried all the way up to 6400iso at F1.4 50mm and could not definitively see the difference. Although from time to time it looked like FX mode was cleaner than the others contrary to what Nikon Recommends.
3.2" SCREEN - Focusing on the screen was OK, I either had to put the camera in AF-S and hit the AF-ON button to focus or use the zoom in feature to get a good focus. I think an external monitor/EVF/etc. would definitely help and recommended. After about 45minutes of live view mode using High ISO, the screen got really grainy and could no longer use live view to focus. I guess the sensor was overheating and introducing a lot of noise
PICTURE CONTROL - Nikon has a Neutral setting which seems to work really well for capturing most dynamic range. I'm not a grading expert, but I think it's a good balance or at least a place to start. I tried customizing my own (based on canon's) and reduced everything except for hue to the minimum. I found in post that I had to sharpen a few shots, so I bumped sharpening up two notches
ACCESS TO MENU - I've customized the front function button and placed all that I could for quick access (WB, IMAGE SIZE, FRAME SIZE/RATE) otherwise you're hunting clicking all the time to get the movie settings.
MICROPHONE - Wow! I ended up using a lot of the built in Microphone audio and was clean and clear. I don't know if I'd use it for voice, but it handled it really well! down side is you can't adjust the levels when recording.
BATTERY LIFE - I turned off live view when ever I wasn't using it. We shot indoors and outdoors (40F weather) for about 5 hours and had 30% battery life by end of day. I thought for sure I'd have to pull out the back up battery but did not. I recorded about 3.5GB of video that day.
If you have any questions I'd be glad to answer them.
Thanks for Watching!