YouTube displays videos with different aspect ratios based on the platform and video format. The YouTube video player automatically adapts to the size of each individual video.
The YouTube app for Android mobile automatically adapts the player to the size of the video. Whether it's vertical, square or horizontal, the video will fill the screen. The vertical (portrait) video player matches the aspect ratio of the video – getting taller for square and vertical videos, and shorter for widescreen videos.
How vertical videos are displayed
Vertical videos will now be displayed in the video player without black bars on the sides. For example:
A viewer can tap in the bottom-right corner of the video to enter vertical full screen to view the entire video.