I'm currently working on the 3rd-party streaming app for Facebook live. The H.264 specification says 1280x720 video should use Level 3.1 (1,280×720@30).
Which level should I use for 720x1280 video?
The aspect ratio/orientation is irrelevant. The level is the same. But unless you know how to calculate macro blocks per second, it’s best to let the software automatically pick the level.