YouTube now features preview thumbnails for videos on its desktop website. Users can now have a 3-second preview of the video content by simply hovering the mouse pointer over a video. The feature has been up since the end of June, however, few users have had the opportunity since February.
We are already half way through July and YouTube has presented the feature to a majority of users. Users can preview the video content through thumbnails that are similar to GIFs on YouTube home pages, search results, watch page, subscription tab, and trending tab.
Moreover, the previews on YouTube will only be visible to Chrome versions 32 and up and Opera version 19 and up users. The thumbnails on mobile devices have not received the feature yet.
As far as the eligibility for videos to showcase animated thumbnails is concerned, YouTube only generates previews for videos that are more than 30 seconds in length. Live videos do not feature the preview as well. YouTube is using AI to generate previews for videos by taking into account factors such as topic and content of the video. The preview is generated from the first half of the video since the first half is believed to give the best idea of what the content of the video actually is.
YouTubers cannot choose the preview they want to showcase as of now. If you are unable to have a look at the preview for a video within next two days it probably will not have a preview anytime soon.