Youtube Search Algorithm
http://tubularinsights.com/youtube-watch-time/
Like search engines such as Google and Yahoo, Youtube has ranking algorithms. Both Youtube and companies like Google and Yahoo earn money from ad revenue, so it these companies are all interested in promoting quality content whether that be webpages or videos. However, videos cannot be ranked on the same criteria as a web page. Previously, Youtube had ranked their videos based on view count which translated into how many clicks the video got. This proved to be an unreliable indicator or video quality, as content producers would abuse this system with misleading or otherwise enticing titles and thumbnails. Youtube has since refined their ranking algorithm to be based off of “watch time”. This is defined by Youtube as the amount of time in aggregate that your viewers are watching your videos.
Although the motives for the ranking algorithms of search engines and Youtube are very similar, Youtube’s ranking algorithm is much different than the PageRank algorithm. Youtube’s ranking algorithm does not have analogs to the hubs and authorities, as it does not use the same type of links. Rather, it seems that the “links” on youtube are directed from the viewer to the videos that they watch. Unlike PageRank, it does not seems that Youtube weights the values of the sources of these links as hubs are ranked. Rather, it seems that each viewer has equal weight in contributing to the score of a video. Also, PageRank uses the concept of “repeated improvement” to cyclically refine scores based on initial improvements to hub and authority scores. Intrinsically, this is not a feature of Youtube’s ranking algorithm because there does not seem to be two sets of scores based off of one another, as viewers are not assigned scores analogous to hub scores of PageRank. If there were to be an analog of hub scores for the Youtube ranking algorithm, perhaps the watch time of viewers who watch highly ranked videos would be weighted more heavily; nonetheless, this isn’t explicitly mentioned in the article. It is unlikely that Youtube’s ranking algorithm is as simple as it is presented in this article, but nevertheless, it seems to be different than the PageRank system.