Nate wroteThey are x,y pairs but "offset" is how many entries are zeros at the start. Also, zeros at the end are not output.
 
 :happy:  Thanks for answer, understand !  That means ffd vertices may not ouput 0 data at the end
 I got data like below
             "head": {
               "head": [
                  {
                     "time": 0,
                     "offset": 4,
                     "vertices": [ 0, 0, 0, 0, 0, 0, 0, 0, 0 ]
                  },
                  {
                     "time": 0.3333,
                     "offset": 2,
                     "vertices": [ 10.57, -9.6, -14.2, -1.48, 0, 0, 0, 0, 0, 0, 0 ]
                  },
                  {
                     "time": 0.6666,
                     "offset": 4,
                     "vertices": [ 0, 0, 0, 0, 0, 0, 0, 0, 0 ]
                  }
               ]
            },
Notice, vertices count all odd number, and output 0 data. By your said, it is should be not output 0  :wonder: