  Due to its status as the most popular video sharing platform, YouTube plays
an important role in the online strategy of extreme right groups, where it is
often used to host associated content such as music and other propaganda. In
this paper, we develop a categorization suitable for the analysis of extreme
right channels found on YouTube. By combining this with an NMF-based topic
modelling method, we categorize channels originating from links propagated by
extreme right Twitter accounts. This method is also used to categorize related
channels, which are determined using results returned by YouTube's related
video service. We identify the existence of a "filter bubble", whereby users
who access an extreme right YouTube video are highly likely to be recommended
further extreme right content.
