Camera requirements for Instant messaging mobile APPs (like whatsapp etc...) are not same as standalone camera.
Single universal mode for still camera and video camera:Edit
No need to change camera mode (still camera Vs Video camera). Single universal mode applies to both.
-> Click takes a photo
-> click and hold records video until it is released. (instant messaging clients does not expect a long video recording. so click and hold is feasible option for short videos)
Turning to Landscape and back to portrait:Edit
Instant messaging mobile APP clients usually in portrait mode.
Turning mobile to landscape shall trigger launching camera. and user takes any number of photos/videos.
Turning back to portrait mode exits camera and back to instant messaging and prompt the user to review photos/videos before timeout (after which photos/videos are automatically shared/uploaded).