原文说法有语病，改写后依然存在。

"A crash or "unusual motion” of the vehicle can automatically trigger the camera’s recording function, the recorder may not store more than 30 seconds of data before and after the event that triggers its recording function.

30 seconds of data before and after the event
如果是事件触发后开始录像，怎么可能录到触发前30秒的视频？那时还没开机呢。