The present invention relates to a video purchasing method, a video playing method, a server and a video playing device. The video purchasing method comprises: receiving a request of a user for purchasing a video file, the request including starting time and ending time of part of the video contents in a complete video file selected by the user; determining starting frame and ending frame to which the starting time and the ending time correspond; and generating the video file to which the part of the video contents corresponds according to the starting frame and the ending frame. According to the method, the user may purchase video contents as needed, and need not purchase the whole video file, which not only brings convenience to users, but also saves costs.