I don’t know much about how lazy loading works so I don’t have any documentation for it. I’m planning to add the feature at some point in the future but it’s been on my list for over a year now. The documents for building Video.js skins are no longer available because the current version of Video.js is very different from the version that ships with my plugin and the old skins don’t work anymore. I’m working on an update to that but I don’t have much time available right now. Because video thumbnails start out as inline attributes of the video element, I don’t think it’s as simple as adding a CSS class to the thumbnail image. For the same reason it’s difficult to make video thumbnails responsive using srcsets.
