According to them, “We are now taking into account more interactions with videos that we have learned indicate whether someone found that video interesting, such as choosing to turn on sound, making the video full screen, and enabling high definition. So if you turn the volume up or make the video full screen, we have updated News Feed to infer you liked the video and will show you similar videos higher up in your News Feed.”
Of course this isn’t always accurate. For example sometimes videos are recorded with poor audio quality or are recorded too loud, thus forcing users to adjust the volume in order to get an idea of what’s happening. It is not necessarily an indicator that we like that particular video, but perhaps over time Facebook will be able to refine their algorithm.
As for owners of Pages or for those who have followed or liked certain Pages, Facebook reassures that they “do not expect most Pages to see significant changes in distribution as a result of this update.”