In the latest build of OnePlus’ Oxygen OS Open Beta for the OnePlus 7T and 7T Pro, a couple of new changes to the camera were added that enable a couple of new video recording modes. While the official changelog was posted over at the OnePlus Forums, it didn’t make mention of these new video modes.
The feature was first discovered by Reddit user sneakerspark and this screenshot was posted to that thread. Others chimes in confirming the ultrawide camera’s addition of a 4K recording option.
Oxygen OS Open Beta 3 for both the 7T and 7T Pro have enabled 960fps slo-mo at 720p resolution. Currently, all OnePlus devices since the OnePlus 6 Pro can only record at 480fps at the same resolution. Since neither the ultrawide or main 48MP sensors on the 7T have the hardware needed to record at 960fps, the additional frames are interpolated from 480fps.
The other addition is an option to record 4K video using the ultrawide camera. Neither the OnePlus 7 Pro, nor the OnePlus 7T offered this feature, but the 7 Pro was updated to unlock the new recording resolution with the ultrawide camera – it just took a while before the 7T would be updated for the same feature.OnePlus 7T
There's still no word from OnePlus as to when these features would arrive in official the official builds of Oxygen OS - it hasn't even mentioned them in the changelog.