Should I upload a video to YouTube in 1080p or 720p?

This is what Google/YouTube talk about Aspect ration (use url link for full details)

Recommended upload encoding settings (Advanced)

Resolution and aspect ratio

YouTube uses 16:9 aspect ratio players. If you are uploading a non-16:9 file, it will be processed and displayed correctly as well, with pillar boxes (black bars on the left and right) or letter boxes (black bars at the top and bottom) provided by the player. If you want to fit the player perfectly, encode at these resolutions:

2160p: 3840x2160

1440p: 2560x1440

1080p: 1920x1080

720p: 1280x720

480p: 854x480

360p: 640x360

240p: 426x240

The YouTube player automatically adds black bars so that videos are displayed correctly without cropping or stretching, no matter the size of the video or the player.

For example, the player will automatically add pillarboxing to 4:3 videos in the new 16:9 widescreen player size. If the player is re-sized (i.e. when embedded on another website), the same process takes place so that 16:9 videos are letterboxed when the player is sized to 4:3. Similarly, anamorphic videos will be automatically letterboxed when shown in either 16:9 or 4:3 sized players. The player can only do this if the native aspect ratio of the video is maintained.

USE URL LINK FOR FULL DETAILS

Hope above answer will be helpful.

Youtube 720p

It depends the device, if you upload in 1080p, phones/tablets that can display 1080p will play in that, phones that can't will automatically play it in 720p. I say upload in 1080p.

I think you should try 1080p, because if I'm right, if that is the case then it automatically goes to 720p or lower on mobile devices. I recommend posting it in 1080p and then checking it on your phone to be sure, though :)

720p, since 1080 isn't available on mobile devices. Plus, it will take yeaaars to upload a video in 1080 to YouTube.

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