H.264 level for vertical video

[madada]

Hi all,

I am planning to re-encode a collection of home videos with the main goal to make them very universally compatible. To that end, I am making an encoding plan.
I want to encode video to the AVC/H.264 format with x264 and audio to AAC and mux them in MP4 containers. I want to choose the lowest H.264 levels I can get away with based on the frame size/resolution of the videos, and for low resolution videos that I'll encode with level 3.0 or lower, I want to choose Main Profile instead of High profile for playback on e.g. old iPads.

I noticed that a lot of encoding software will adjust settings based on the chosen level. For example, when encoding a 720p video with Handbrake using x264's "veryslow" profile, having chosen level 3.1, the software will limit the amount of used reference frames to fit the maximum allowed by the level. However, I also noticed that other software sometimes doesn't comply, so I want to be sure of what I'm doing, therefore the following question.

When encoding a vertical video to a frame size/resolution of 720*1280 (so, not 1280*720), can I still use level 3.1 (the lowest level that allows horizontal 720p)? Or is a vertical frame size of more than 720 pixels not allowed?

Side note: I know some vertical videos created by phones are actually rotated horizontal videos but have a tag that tells the video player how to rotate "back" upon playback. I also read that this tag is not standardized. Is this correct?

[Selur]

Resolution is only looked at as frame size in macroblocks (16x16) regarding the minimal required level so whether it's 1280x720 or 720x1280 doesn't matter since they cover the same amount of macroblocks.
(iirc the main problem with the rotate flag is that not all players support it)

[madada]

Originally Posted by Selur

Resolution is only looked at as frame size in macroblocks (16x16) regarding the minimal required level so whether it's 1280x720 or 720x1280 doesn't matter since they cover the same amount of macroblocks.
(iirc the main problem with the rotate flag is that not all players support it)

Okay, that's very good to know.
Thanks for your answer!