Here is the license information on using music in a video series:
What constitutes a series (eg TV series, webisodes, or a magazine with monthly editions)?
To be considered a series, all things in the series (eg episode, edition) must be connected, and be released within 1 year of the first installment. There is also a maximum of 52 episodes or editions within the series.
Example: A 12 episode TV series that starts in December and ends in July would only require a single license. A YouTube series that releases an episode every week (52 total) would only need to purchase a license once every year. A magazine that releases an edition every other month would need to purchase a license once every year.