1. A method for generating a series of still images from a video file, the method comprising: extracting, by a multimedia management computing device, a plurality of audio frames and a corresponding plurality of visual frames from a video file; identifying, by the multimedia management computing device, a plurality of basic units of the video file, each of the plurality of basic units comprising a respective subset of the plurality of visual frames and a corresponding subset of the plurality of audio frames; extracting, by the multimedia management computing device, for each of the plurality of basic units, one or more key visual frames from the subset of the plurality of visual frames and corresponding one or more key audio frames from the subset of the plurality of audio frames; generating, by the multimedia management computing device, a speaker dialogue graph based on the one or more key audio frames; identifying, by the multimedia management computing device, one or more characters based on the generated speaker dialogue graph; converting, by the multimedia management computing device, the one or more key visual frames into a series of still images and the corresponding one or more key audio frames into text corresponding to the one or more characters; and outputting, by the multimedia management computing device, the series of still images and the text corresponding to the one or more characters.