docs: def load(self, filepath):
          """Load the track file"""
          with open(filepath, 'rb') as fd:
              num_keys = struct.unpack(">i", fd.read(4))[0]
              for i in range(num_keys):
                  row, value, kind = struct.unpack('>ifb', fd.read(9))
                  self.keys.append(TrackKey(row, value, kind))