Detection of video double encoding with GOP size estimation

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Detection of image resampling and video encoding footprints for forensic applications

Multimedia contents play an important role in our society. They serve as a means of communication and can be used not only as an entertainment, but also to inform or even to disseminate knowledge. The increasing relevance of multimedia contents, such as digital images, audio, or video sequences, has been tied to the development of editing software tools enabling their adjustment and enhancement, but ultimately allowing an unskilled person to easily manipúlate them. As a consequence, their credibility as a source of information has been questioned and an important concern has arisen regarding their authenticity. With the aim of recovering trust on multimedia objects, this thesis presents new techniques to detect and localize forgeries, but likewise to infer information about the processing history undergone by a multimedia content. The design of the proposed approaches is based on the theoretical analysis of characteristic traces or footprints that emerge from the application of certain processing to multimedia contents. In this thesis the derived research work encompassing multimedia forensics is divided in two parts. The first part tackles the study of the resampling operation applied when a geometric transformation is performed to adapt a forged content to a genuine scene. The modeling of the resampling operation is addressed from different perspectives, establishing connections between this problem and other similar ones arising in distinct fields, and finally taking advantage of concepts from cyclostationarity theory, set-membership theory, or linear algebra, among others. We design different strategies for resampling factor estimation to characterize the particular transformation applied, providing estimates of the scaling factor or the rotation angle. The case of resampling detection is also considered to unveil the presence of resampling traces. The second part of the thesis is focused on the forensic analysis of video compressed sequences. We start exposing the presence of a new footprint stemming from the double compression of video streams. By exploiting this feature, the detection of double encoding and the estimation of part of the processing history of a double compressed video are further investigated. Then, being capable of extracting information from the first compression, we move to the localization of intra-frame forgeries by applying a subsequent double quantization analysis

Preventing and Mitigating Alcohol Toxicity: A Review on Protective Substances

This review covers three fundamental aspects of alcohol consumption and research efforts around the prevention and mitigation of its toxic effects in the human body. First, the sociocultural aspects of alcohol consumption are analysed, including drinking habits and strategies to combat intoxication. Second, we briefly introduce the biochemical aspects of ethanol metabolism and the biochemical pathways leading to its degradation, particularly the activation of toxic response pathways. Finally, we review current evidence and research efforts for finding compounds and substances able to prevent and mitigate the toxic effects of alcohol when over-indulgence has occurred. The toxic effects appear as a time-evolution process based on the stage of intoxication. We explore different compounds and formulations traditionally used to combat alcohol toxicity, as well as state-of-the-art research in the topic for novel molecules and formulations. Although we aimed to categorise which compounds are more effective for a particular level of alcohol intoxication, it is impossible to fully prevent or mitigate toxicity effects by only the compounds in isolation, further research is required to establish the long-term prevention and mitigation from the clinical point of view

Video Integrity Verification and GOP Size Estimation Via Generalized Variation of Prediction Footprint

The Variation of Prediction Footprint (VPF), formerly used in video forensics for double compression detection and GOP size estimation, is comprehensively investigated to improve its acquisition capabilities and extend its use to video sequences that contain bi-directional frames (B-frames). By relying on a universal rate-distortion analysis applied to a generic double compression scheme, we first explain the rationale behind the presence of the VPF in double compressed videos and then justify the need of exploiting a new source of information such as the motion vectors, to enhance the VPF acquisition process. Finally, we describe the shifted VPF induced by the presence of B-frames and detail how to compensate the shift to avoid misguided GOP size estimations. The experimental results show that the proposed Generalized VPF (G-VPF) technique outperforms the state of the art, not only in terms of double compression detection and GOP size estimation, but also in reducing computational time

Localization of Forgeries in MPEG-2 Video through GOP Size and DQ Analysis

This work addresses forgery localization in MPEG-2 compressed videos. The proposed method is based on the analysis of Double Quantization (DQ) traces in frames that were encoded twice as intra (i.e., I-frames). Employing a state-of-the-art method, such frames are located in the video under analysis by estimating the size of the Group Of Pictures (GOP) that was used in the first compression; then, the DQ analysis is devised for the MPEG-2 encoding scheme and applied to frames that were intra-coded in both the first and second compression. In such a way, regions that were manipulated between the two encodings are detected. Compared to existing methods based on double quantization analysis, the proposed scheme makes forgery localization possible on a wider range of settings

Fouling mitigation by cationic polymer addition into a pilot‐scale anaerobic membrane bioreactor fed with blackwater

Cationic polymers have proven to be suitable flux enhancers (FEs) in large‐scale aerobic membrane bioreactors (MBRs), whereas in anaerobic membrane bioreactors (AnMBRs) research is scarce, and so far, only done at lab‐scale. Results from MBRs cannot be directly translated to AnMBRs because the extent and nature of membrane fouling under anaerobic and aerobic conditions are different. Our research focused on the long‐term effect of dosing the cationic polymer Adifloc KD451 to a pilot AnMBR, fed with source‐separated domestic blackwater. A single dosage of Adifloc KD451 at 50 mg L−1 significantly enhanced the filtration performance in the AnMBR, revealed by a decrease in both fouling rate and total filtration resistance. Nevertheless, FE addition had an immediate negative effect on the specific methanogenic activity (SMA), but this was a reversible process that had no adverse effect on permeate quality or chemical oxygen demand (COD) removal in the AnMBR. Moreover, the FE had a long‐term positive effect on AnMBR filtration performance and sludge filterability. These findings indicate that dosing Adifloc KD451 is a suitable strategy for fouling mitigation in AnMBRs because it led to a long‐term improvement in filtration performance, while having no significant adverse effects on permeate quality or COD removal.</p