I have a samsung galaxy S8 and I cast my phone screen to my Tv using a google chromecast.
whenever I take photos or video I always shoot in landscape mode, never in portrait mode.
the problem i have is I'd like to record video on my phone while at the same time casting to TV so I can monitor the live image on the TV. but when I open the camera on the phone the image on the TV locks into portrait mode (see the picture attached). the image on the phone itself is correct but it's on is side on the TV.
all other functions on the phone work fine in landsape mode and they cast correctly to the tv in landscape mode but the opening the camera app suddenly flips the TV image on its side into portrait mode. any solution to this?
thankyou but the rabbit hole just goes deeper.
if I search for apps on my phone there is no smart view (screenshot 1). however I do have a smart view app that appears in my settings (screenshot 2) but all that does is give me app info and the the disable button is greyed out (screenshot 3) which tells me the app may not be enabled in the first place. still scratching my head....
at the lnk you gave it says:
"Screen rotation displays content in landscape (horizontal) or portrait (vertical) and isn't available for all apps"
I have a feeling in my bones that screen rotation is not supported in the camera app. I managed to lock the screen in landscape mode and my homepage and all other apps appeard in landscape mode screenshot 1). but when I opened the camera app the screenshot was in portrait mode (screenshot 2). unless I'm mistaken the the camera appears to be cemented into portrait mode and nothing will change it.
when I took screenshot2 I was holding the camera in landscape position.
thankyou I did find smart view under the drop down menu however when I switched the camera on (while casting to the TV) this message briefly appeared on both the phone and the TV 
