1. A method for summarizing unknown content of a video, comprising: selecting low-level features of the video; partitioning the video into segments according to the low-level features; grouping the segments into a plurality of disjoint clusters, each cluster containing similar segments; labeling the plurality of clusters according to the low-level features; finding high-level patterns among the labels; and extracting frames from the video according to the high-level patterns to form a content-adaptive summary of the unknown content of the video.