Flexible Macroblock Ordering

Abstract: This paper proposes two data hiding approaches using compressed MPEG video. The first approach hides message bits by modulating the quantization scale of a constant bitrate video. A payload of one message bit per macroblock is achieved. A second order multivariate regression is used to find an association between macroblock-level feature variables and the values of a hidden message bit. The regression model is then used by the decoder to predict the values of the hidden message bits with very high prediction accuracy. The second approach uses the flexible macroblock ordering feature of H.264/AVC to hide message bits. Macroblocks are assigned to arbitrary slice groups according to the content of the message bits to be hidden. A maximum payload of three message bits per macroblock is achieved. The proposed solutions are analyzed in terms of message extraction accuracy, message payload, excessive bitrate and quality distortion. Comparisons with previous work reveal that the proposed solutions are superior in terms of message payload while causing less distortion and compression overhead.

Abstract: With the increase of terrorist and criminal activities, closed circuit television (CCTV) is widely used on many occasions. However, abuse of surveillance video may result in the leakage of personal privacy. To protect the privacy in the video of CCTV, an encryption scheme for region of interest (ROI) of H.264 video based on flexible macroblock ordering (FMO) and chaos is proposed in this paper, where human face regions are selected as an example of ROI. First, the human face regions in the video are detected and extracted. Then, they are mapped into slice groups by using FMO technology in H.264. After that, these regions are encrypted using selective video encryption based on chaos. Experimental results and analysis show that the proposed scheme can effectively protect the private information of H.264 video and, therefore, can strike a good balance among the security, encryption efficiency, and coding performance. It has great potential to be used in the privacy protection of the video of CCTV.

Abstract: We propose a unifying framework for efficient encoding, transmission, and quality assessment of atherosclerotic plaque ultrasound video. The approach is based on a spatially varying encoding scheme, where video-slice quantization parameters are varied as a function of diagnostic significance. Video slices are automatically set based on a segmentation algorithm. They are then encoded using a modified version of H.264/AVC flexible macroblock ordering (FMO) technique that allows variable quality slice encoding and redundant slices (RSs) for resilience over error-prone transmission channels. We evaluate our scheme on a representative collection of ten ultrasound videos of the carotid artery for packet loss rates up to 30%. Extensive simulations incorporating three FMO encoding methods, different quantization parameters, and different packet loss scenarios are investigated. Quality assessment is based on a new clinical rating system that provides independent evaluations of the different parts of the video (subjective). We also use objective video-quality assessment metrics and estimate their correlation to the clinical quality assessment of plaque type. We find that some objective quality assessment measures computed over the plaque video slices gave very good correlations to mean opinion scores (MOSs). Here, MOSs were computed using two medical experts. Experimental results show that the proposed method achieves enhanced performance in noisy environments, while at the same time achieving significant bandwidth demands reductions, providing transmission over 3G (and beyond) wireless networks.

Abstract: In this paper, we address the problem of privacy in video surveillance systems. More specifically, we consider the case of H.264/AVC which is the state-of-the-art in video coding. We assume that regions of interest (ROI), containing privacy-sensitive information, have been identified. The content of these regions are then concealed using scrambling. More specifically, we introduce two region-based scrambling techniques. The first one pseudo-randomly flips the sign of transform coefficients during encoding. The second one is performing a pseudo-random permutation of transform coefficients in a block. The flexible macroblock ordering (FMO) mechanism of H.264/AVC is exploited to discriminate between the ROI which are scrambled and the background which remains clear. Experimental results show that both techniques are able to effectively hide private information in ROI, while the scene remains comprehensible. Furthermore, the loss in coding efficiency stays small, whereas the required additional computational complexity is negligible.