In a network video recorder (NVR), a starting location and an end location of video data in a file are set. One frame of video data is recorded in one element of a storage buffer and the element has an index. The NVR further sets a starting location and an end location that coincides with the index of a frame of video data in the storage buffer. If the NVR receives a frame and not enough space of the storage buffer, the NVR adjusts the starting location of the storage buffer by one element, and adjusts the starting location of the file to the starting location of the frame in the storage buffer. If enough space is and the frame is the Intra-frame, the NVR adjusts the end location of the file by one frame, and adjusts the end location of the storage buffer by one element.