video streaming in youtube

Hi...everybody in forum....I am analysing traffic on a WLAN using wirshark.....And when i do staistics using wireshark...i am having a problem to understand ....."i am downloading video file from youtube and using i/o graph to analyse udp and tcp traffic but it always show me tcp much more than udp...But my understanding is when i click to play file it shold be a handshake using tcp and then udp starts working.......But during the whole video tcp is with udp and its very high.......

Can anybody help...why is this...