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OIS is only for photos on the 6+, doesn't effect video.

Not sure about this.

During the presentation on release day, a video clip was shown of a person using the 6+ and filming the scenery outside the vehicle while it was moving to demonstrate this exact feature
 
The 6+ doesn't use IOS for video.

The 6 and 6+ use what Apple calls, cinematic video stabilisation.
 
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