Barry Schwartz covered this new update on Friday at Search Engine Land. YouTube has added the ranking factors to YouTube Search - the new ranking factor is time viewed.
Now, depending on how much time someone watched your video on YouTube (I guess based on the video length), the more whole video is viewed then your video will be number one on YouTube search results.
YouTube also added time viewed to YouTube Analytics so, anyone can easily see how well their videos are performing in terms of time watched.
I have samples which show you some stats from the videos on Barry Schwartz Channel:
Google’s YouTube wrote:
The experimental results of this change have proven positive — less clicking, more watching. We expect the amount of time viewers spend watching videos from search and across the site to increase. As with previous optimizations to our discovery features, this should benefit your channel if your videos drive more viewing time across YouTube.
Friday's Video:
