Being a mobile-first service, Instagram’s new IGTV video sharing platform is built around the needs of smartphone users. The app only allows vertical videos, and it supports only one video format — MP4.
You cannot upload videos recorded in any other format than MP4 on IGTV. And of course, the video recording format on your iPhone and Android are supported by IGTV by default.
On IGTV, you can only upload videos vertically. If you upload a video recorded in Landscape, the service will only display the video vertically by fixing the frame to the center of the video.
As for the file size, for a 10 minutes video, the maximum allowed file size is 650MB. And for 60 minutes long videos, the maximum file size limit is 5.4GB.