YouTube looks to be testing a new layout for its video page after we found watching videos on YouTube a little different to normal. The new UI mimics the homepage feed and moves the description and comments to the right side of the video.
After refreshing the new video page, it reverts to the old page YouTube recently updated. This could mean this is a bug and YouTube isn’t ready to show it off yet, or is just testing it to see how the internet reacts.
In-feed layout
The first change is the new feel of the page. Above and below the current video being watched is a grid of recommended videos. From what we can tell these videos match what was on the home feed before selecting a video to watch.
Based on this, YouTube is wanting to make watching a video feel more inline rather than moving to a new page with a different layout. Depending on the size of your display the number of videos recommended in a line change as well.

Description and comments
The description and comments section have moved to the right side of the video, filling in what used to be the recommended video section. This change means making a comment now take an extra step of clicking on the comments section to get to the comments ‘page’. This is the same for the description and chapters.
Why change the video page?
YouTube’s goal is to keep users on its website and watching videos for as long as possible. By making the video page seem like it’s in the home feed and having the video almost pop out at the user does this. As you scroll away from the video, the mini player pops up in the corner making it easy to continue listening to your video and glance over every so often as well as adding new videos to your queue. Once the video is finished the next will automatically play.