1. A device for previewing a video, the device comprising:a memory device configured to store instructions; and
one or more processors configured to execute the instructions to:
receive the video captured by a camera, wherein the camera includes an image sensor, a sound sensor, and a motion sensor including an ultrasonic sensor;
obtain information relating to a potential special event detected by the camera, wherein the information relating to the potential special event is obtained by at least one of the motion sensor or the sound sensor, the ultrasonic sensor configured to emit ultrasonic signals to detect an object within a vicinity of the camera based on reflected ultrasonic signals and the motion sensor configured to generate a signal indicating that the object is present, the sound sensor configured to generate a signal if the sounds sensor detects an ambient sound level exceeding a threshold, wherein a processor of the camera is responsive to the signal generated by the motion sensor or the sound sensor to instruct the image sensor to start capturing the video;
analyze the captured video;
detect a special event from the analysis of the video by comparing an identified feature with one or more object, motion, or sound models previously constructed, the special event including at least one of an object, a moving object, or a sound detected in the video;
extract, from the video, at least a first video preview frame or audio segment corresponding to the special event based on information relating to the potential special event, wherein the one or more processors are further configured to skip frames before extracting a second video preview frame or audio segment, depending on whether the special event is detected in the first video preview frame or audio segment, wherein the skipped frames correspond to a time period selected by the one or more processors for skipping frames, a length of the time period being selected based on whether the special event is detected in a previous time period; and
generate a preview video including the at least first video preview frame or audio segment corresponding to the special event.