Fix install of ffmpeg since Travis upgrade to trusty
Fix install of ffmpeg since Travis upgrade to trusty

saimn/sigal,t-animal/sigal,xouillet/sigal,xouillet/sigal,jasuarez/sigal,saimn/sigal,t-animal/sigal,xouillet/sigal,t-animal/sigal,saimn/sigal,jasuarez/sigal,jasuarez/sigal