<file-id = -1 (ignore this parameter)>
<num-tracks = 1024 (default)>
x1 y1 1 track-id
x2 y2 1 track-id
..
..
..
x1024 y1024 1 track-id

The track-ids are consistent across all frames, and represent the id of a 3D point that corresponds to each 2D track. 
Note: A track id of -1 indicates an invalid 2D point. 