Characterizing Video Responses in Social Networks
  Video sharing sites, such as YouTube, use video responses to enhance the social interactions among their users. The video response feature allows users to interact and converse through video, by creating a video sequence that begins with an opening video and followed by video responses from other users. Our characterization is over 3.4 million videos and 400,000 video responses collected from YouTube during a 7-day period. We first analyze the characteristics of the video responses, such as popularity, duration, and geography. We then examine the social networks that emerge from the video response interactions. 
Fabricio Benevenuto, Fernando Duarte, Tiago Rodrigues, Virgilio   Almeida, Jussara Almeida, Keith Ross