Every container has a type property, which determines how it and its children are rendered:
container
This is the default container type and is mostly used for the "home" container. This type indicates that the children should be rendered as rows. If this type is already in a row, the thumbnail should be rendered in a 2:3 aspect ratio and a click should open a new window/activity.
playlist
This container only contains video containers (playlists). Its item thumbnails should be rendered in a 2:3 aspect ratio.
artist
This container only contains playlist containers. Its item thumbnails should be rendered as circles.
genre
This container only contains playlist containers. Its item thumbnails should be rendered in a 1:1 aspect ratio.
video
This container only contains videos. Its item thumbnails should be rendered in a 16:9 aspect ratio.