Query by video clip (QVC) has attracted wide research interests in multimedia information retrieval. In general, QVC may include feature extraction, similaritymeasure,databaseorganization,andsearchorqueryscheme.Towardsan effective and efficient solution, diverse applications have different considerations and challenges on the abovementioned phases. In this paper, we firstly attempt to broadly categorize most existing QVC work into 3 levels: concept based video retrieval, video title identification, and video copy detection. This 3-level categorization is expected to explicitly identify typical applications, robust requirements, likely features, and main challenges existing between mature techniques and hard performance requirements. A brief survey is presented to concretize the QVC categorization. Under this categorization, in this paper we focus on the copy detection task, wherein the challenges are mainly due to the design of compact and robust low level features (i.e. an effectiv...