Detection of Double Compressed HEVC Videos Using GOP-Based PU Type Statistics

Double compression detection is of great significance to recover the compression history of suspicious videos and help analyzers locate tampering points in forged videos. However, the lack of efficient methods still haunts researchers when it comes to double HEVC compression detection with a shifted group of pictures (GOP) structures. To tackle this problem, we first analyze the properties of re-encoded frames in double compressed HEVC videos. It is found that the abnormal statistics of prediction unit (PU) types in relocated I-frames can be used as the clue to expose double compression. Relocated I-frames are re-encoded P-frames, which were I-frames in the first compression. Different from the existing works, we designed the GOP-based features instead of frame-based features, enabling more efficient utilization of temporal variation patterns of PU-type statistics within each GOP unit. In the proposed method, the ratio of I-PUs and S-Pus is first computed to construct PU sequences for each GOP unit. The three-tap median filter is applied to PU sequences in order to mitigate the influence of various video contents. Several first-order statistics, including average, variation, and maximum/minimum, are selected to generate a 6-D detection feature. Then, multi-layer perceptron (MLP) is used to classify GOP-based features. Finally, the score fusion strategy is applied to obtain the detection result of the input video. Several publicly available YUV sequences are used to construct the double compression dataset with various coding parameters. In experiments, the proposed method outperforms several state-of-the-art methods under different settings of bitrates and GOP structures. The proposed method has more robust detection capability even when tampered videos are generated by combining two video clips with different GOP sizes.