If you’re wanting to add an Asset Library to your SharePoint site but not finding it available as an option, chances are the Video and Rich Media feature for that site collection isn’t activated. This feature enables the asset library which is basically a modified document library but with metadata specific to rich media that can be auto-extracted such as width and height of images, duration of video clips, etc. Asset libraries are good for storing your audio, video, and image content types.
To enable it (as a site collection admin) go to Settings > Site Settings and choose Site collection features from under the Site Collection Administration heading.
Then scroll down and look for the Video and Rich Media feature. Click Activate.
As the description says, this will “[provide] libraries, content types, and web parts for storing, managing, and viewing rich media assets, like images, sound clips, and videos.” Once activated, you’ll now be able to add the asset library to your site(s) in that collection.