I got some info about the mystery switch on the Nikon D3100 - the body has two new controls:
- To the right of the mode dial is a sliding switch which arcs around it (similar to the Panasonic G1, GH1, G2). This selects drive modes between Single, Continuous, Self-timer and Quiet (which holds the mirror up until you let go of the shutter release after a shot).
- Above the multi-selector on the back and a bit further to the left towards the screen is a lever to activate live view, and inside the pivot point of the lever is a red button to start video recording.
And some more video details:
- Video options: 1080 24 fps, 720 30/25/24 fps, and 640x424 24 fps.
- The D3100 video is H.264, with 16 bit 24 KHz audio, in a .MOV container. The 24 fps is actually a proper 23.976 fps that video professionals expect.
- AVCHD video codec : the D3100 just stores a single .MOV file for each movie in the same directory as your still photos, so it is technically not AVCHD, but it uses the same technology.