Some time ago, Youtube began to offer a more detailed analysis of video views, including graphs of views per day. I just came across the all-time most viewed video, i.e. Psy's Gangnam style, and something on this graph (attached) struck me : a neat periodic pattern emerges among some other things (the increase around new year's day due to "one billion views" publicity, the recent surge (?), and the smooth overall curve).
The video was posted of 15th of July 2012 and the graph is said to account for views until 4th of July 2013. It therefore spans 354 days. The graph is also 475 pixels wide. So each pixel day represents approximately 1.34 days pixels. Now the mean wavelength of these oscillations is rougly 9.5 ± 0.5 pixels (almost all peaks are spaced by 9 or 10). This was measured on graph, i didn't bothered running a mathematica script but that seems a fair approximation. This gives us 12.75 ± 0.67 days 6.70± 0.37 days.
I checked his video release dates (as it seems to happen after the initial "viral spread" making him famous). It sometimes fits, but that not as periodic by a long shot, so if that's linked (and it seems likely), it only partly explains the periodicity. Perhaps it's a real, meaningful sociological phenomenon ; or perhaps it's just a Youtube glitch (too many views to process so it's released in bunches?). I don't have the slightest idea to be frank. Someone ? People watch it on Sundays.
edit: fixed.