Here, I'll be looking into how it actually works. By removing the lens, it is possible to look straight into the sensor, to see how it moves during video recording. To video record the sensor, inside the lens mount, I put the Lumix GH4 with the Samyang 7.5mm f/3.5 fisheye lens pointing straight into the E-M5:
For an even lightning, I put some white paper around the Samyang fisheye lens. The lens was set to the closest focus distance, and f/8 for sufficient depth of focus.
When moving the camera around, one can see how the sensor also moves, to stabilize the video:
In this case, I left the focal length setting at 15mm on the Olympus OM-D E-M5 Mark II. Setting it higher would make the sensor move more.
The IBIS (In-body image stabilization) of the Olympus OM-D E-M5 Mark II makes it very useful for handheld video recording. However, it is a shame that it involves cropping the sensor during video, so that you need even wider lenses.