用定时器触发停止录像

平台：iOS
在使用MSDK设置录像的航点动作时，可以设置录像时长吗？
看SDK中的注释，好像只能使用停止录像动作来终止录像，有没有办法可以控制录像时长

下面是SDK中的相关注释          

     *  Starts recording. The `actionParam` for the waypoint action will be  ignored.

     *  The maximum time set to execute this waypoint action is 6 seconds. If the time

     *  while executing  the waypoint action goes above 6 seconds (e.g. the camera is

     *  not present) the aircraft will stop executing  the waypoint action and will move

     *  on to the next waypoint action, if one exists.

     DJIWaypointActionTypeStartRecord,

     *  Stops recording. The `actionParam` for the waypoint action will be ignored.  The

     *  maximum time set to execute this waypoint action is 6 seconds. If the time while

     *  executing the waypoint  action goes above 6 seconds (e.g. the camera is not

     *  present) the aircraft will stop executing the waypoint  action and will move on

     *  to the next waypoint action, if one exists.

     DJIWaypointActionTypeStopRecord,

用定时器触发停止录像