Starting on May 23, when a horizontal video is uploaded to IGTV, a miniaturized version of it will appear in the platform’s vertical-by-default video player, with black bars above and below it to denote it as a horizontal video. Viewers will be able to rotate their phones or tap a button to expand the video to play at full screen in landscape mode.
Even though the majority of services and trends in video says differently, I'm still a big believer in horizontal video. I've gotten used to watching stories vertically, but anywhere else still drives me nuts. I'm not a huge user of IGTV, but this may change that.
https://instagram-press.com/blog/2019/05/23/igtv-now-supports-landscape-videos/