YouTube loves to change their design, but I don’t blame them since every company wants to keep their site new, relevant and improving. The newest thing YouTube did to their design is the “YouTube One Channel”. It is a new design that makes your YouTube identiy the same on all devices, such as computers, phones, tablets and TV’s.
What do I mean by identity? Your channel “cover image” will remain the same on all devices, but will be different sizes and the larger the devices screen the more they will see. For instance phones and small screen computers will see a 1280px by 360px image. Tablets will see 1536px by 360px and other devices larger. This is a great thing to keep your viewers knowing that it is your channel. The first thing they will see is the header and right away they will know it is your channel. To view how to size your cover image, look at this post by YouTube on the Google Support Pages
Other than the cover image they added “Unsubscribed Trailer”. This is a video you add for only unsubscribed viewers to watch. It is a place to convince visitor to subscribe. YouTube and others suggest you keep this video under 1 minute. It should contain what your channel is about, what type of content you create, who you are trying to target and why they should subscribe.
With your trailer, make it like your other videos and possibly show clips or your channels personality. For instance if you are a comedian, you better make a comedic trailer. Like all the other content you upload, just be yourself.
The last thing they are introducing are “shelves”. These are rows of videos, playlists and uploads. You can setup your most popular content to be the first seen and then recent uploads, and show off some playlists. They added many options other than just showing off playlists and uploads, you have a more dynamic listing type.
If you would like to start using the new YouTube layout, visit the YouTube One page here, and you can also get more information on that page.