Multiple compression detection for video sequences

Nowadays, thanks to the increasingly availability of powerful processors and user friendly applications, the editing of video sequences is becoming more and more frequent. Moreover, after each editing step, any video object is almost always encoded in order to store it using a less amount of memory. For this reason, inferring the number of compression steps that have been applied to such a multimedia object is an important clue in order to assess its authenticity. In this paper we propose a method to recover the number of compression steps applied to a video sequence. In order to accomplish this goal, we make use of a classifier based on multiple Support Vector Machines (SVM) exploiting the Benford´s law. Indeed, the feature vectors used to train and test the SVM are based on the statistics of the most significant digit of quantized transform coefficients. The proposed method is tested with a generic hybrid video encoder combining motion-compensation and block coding. Results show that this method is able to discriminate up to three compression stages with high accuracy.