According to an article by ReelSEO Google made an essential change regarding indexing of YouTube videos aka websites having video embedded. In particular this concerns Google Video, the part of Google enabling to search for video in particular.
Up to now there has been a strong correlation between websites and videos hosted at the same webspace and video sitemaps. Like the common sitemap feature, which communicates the sites available under a domain, the video sitemaps communicated the videos available under a domain and the relevant webpages where these videos are placed. In short there has been a correlation between videos indexed and hosts of the videos.
The essential change mentioned above dismisses this correlation of websites and hosting of videos. Now the hosting of videos no longer is a precondition to sites being indexed by the Google Video search and sites having videos embedded are indexed as well. This at least is due to YouTube videos being placed on sites. ReelSEO has surveyed this issue and made available a comprehensive article about it: Google Now Indexing URLs with Embedded YouTube Videos.