This work introduces a novel approach for correcting a single-bit error in a CRC-protected message, which is based on a perfect hash table that can be queried by a non-zero CRC syndrome. The paper primarily focuses on presenting the new table structure and includes a comparative analysis of various CRC-based error correction methods, demonstrating that ours strikes an excellent balance between correction complexity and memory requirements. Complexity evaluation is performed in terms of the number of 2-input gate operations.

Image communication increasingly involves machine-to-machine delivery. For example, images acquired by an autonomous drone can be compressed and sent to an edge server over a wireless network for resource-intensive processing. Traditional compression techniques involving transform, quantization, and entropy coding reach high compression efficiency, but channel conditions worse than expected may lead to a sharp decrease in the decoded image quality. As an alternative, Linear Coding and Transmission (LCT) systems have been proposed to avoid this digital cliff problem: The reconstructed image quality decreases gradually as channel conditions degrade. This paper presents a comprehensive evaluation of computer vision tasks with input images processed and transmitted using LCT. It also analyses the benefits of network retraining, accounting for impairments due to LCT and noisy channel. Considering object detection and semantic segmentation over images transmitted and received by LCT systems, we show that the task accuracy degrades smoothly when the channel quality decreases, avoiding the cliff effect. Retraining with noisy images processed by LCT restores detection mAP degradation from 23.8% to 4.4% and segmentation mIoU degradation from 43.2% to 8.1 % when the channel signal-to-noise ratio is 10 dB.

Applications such as teleoperated driving, remote robot control, and telepresence rely on video services to ensure real-time interaction with a satisfying quality of experience. Reducing the Glass-to-Glass (G2G) delay, i.e., the time delay between the acquisition of a video frame and its display on a remote terminal is critical for these applications. Deep learning-based video frame extrapolation before video encoding has been recently considered as an interesting solution to reduce G2G delay, however, the latency introduced by extrapolation has not been taken into account. In this paper, considering the main sources of latency, including extrapolation delay, we examine the benefits and limitations of frame extrapolation at encoder in reducing the G2G delay in a point-to-point video transmission system. To this end, we compare the latency-quality trade-off for two latency compensation methods: encoding rate reduction and video frame extrapolation. Our aim is to determine the G2G delay reduction that may be achieved at the price of a given quality reduction. Our experiments show that extrapolation methods can provide a null perceived G2G delay with an acceptable loss in quality, particularly for applications with video contents with limited temporal information. Such delay reduction is unreachable via encoding rate reduction.

In this paper, we propose a new deep learning-based quality ranking framework to assist video list decoding methods in the context of unreliable video transmissions. The objective is to identify an intact image (corrected video frame) among a list of candidate images generated by a list decoding method, where all candidates, except for the intact image are corrupted. The framework comprises a deep learning-based no-reference image quality assessment (NR-IQA) for non-uniform video distortions (NUD) system to rank the candidate images according to their quality, which allows identifying the best one. To show the validity of our proposed framework, we develop an NR-IQA system relying on a proven patch-based convolutional neural network (CNN) architecture, which we adapt to better account for the non-uniform distortions observed in the candidate images, e.g., H.265 transmission errors during wireless communications. Specifically, we modify the patch size on which our CNN for non-uniform distortions (CNN-NUD) operates to capture a larger and more meaningful spatial context. Moreover, we develop a new training database using images resulting from various bit modifications in the received video packets, to simulate the list decoding process, and train the system using a full reference IQA (FR-IQA) method. Experiments on intra frames of videos encoded using H.265 show the ability of this system to identify an intact image among a set of five candidate images with an average accuracy of 96.6%, whereas traditional NR-IQA metrics or the initially trained CNN system offer poor accuracy ranging between 15.7% and 33.6%, respectively.

The SoftCast scheme has been proposed as a promising alternative to traditional video broadcasting systems in wireless environments. In its current form, SoftCast performs image decoding at the receiver side by using a Linear Least Square Error (LLSE) estimator. Such approach maximizes the reconstructed quality in terms of Peak Signal-to-Noise Ratio (PSNR). However, we show that the LLSE induces an annoying blur effect at low Channel Signal-to-Noise Ratio (CSNR) quality. To cancel this artifact, we propose to replace the LLSE estimator by the Zero-Forcing (ZF) one. In order to better understand the perceived quality offered by these two estimators, a mathematical characterization as well as an objective and subjective studies are performed. Results show that the gains brought by the LLSE estimator, in terms of PSNR and Structural SIMiliraty (SSIM), are limited and quickly tend to null value as the CSNR increases. However, higher gains are obtained by the ZF estimator when considering the recent Video Multi-method Assessment Fusion (VMAF) metric proposed by Netflix, which evaluates the perceptual video quality. This result is confirmed by the subjective assessment.

This paper analyzes the benefits of extending CRC-based error correction (CRC-EC) to handle more errors in the context of error-prone wireless networks. In the literature, CRC-EC has been used to correct up to 3 binary errors per packet. We first present a theoretical analysis of the CRC-EC candidate list while increasing the number of errors considered. We then analyze the candidate list reduction resulting from subsequent checksum validation and video decoding steps. Simulations conducted on two wireless networks show that the network considered has a huge impact on CRC-EC performance. Over a Bluetooth low energy (BLE) channel with Eb/No=8 dB, an average PSNR improvement of 4.4 dB on videos is achieved when CRC-EC corrects up to 5, rather than 3 errors per packet.

In this paper, we introduce a novel cyclic redundancy check (CRC)-based single error correction method which we apply to robust H.264 Baseline video decoding. Unlike state-of-the-art methods, the proposed correction algorithm does not require lookup tables as it determines the error location based on binary operations using the computed link layer CRC syndrome. Since multiple errors can lead to the same CRC syndrome as a single error, verification of the corrected packet is performed through a non-desynchronizing bits validation (NDBV), which forwards only compliant packets to the video decoder. Simulations on the H.264 Baseline profile show an average gain of 3.04 dB and 2.36 dB over state-of-the-art spatio-temporal error concealment (STBMA) and NDBV + STBMA reconstruction methods, respectively, at a residual bit error rate of $10^{-6}$.

SoftCast-based linear video coding and transmission (LVCT) schemes have been proposed as a promising alternative to traditional video coding and transmission schemes in wireless environments. Currently, the performance of LVCT schemes is evaluated by means of traditional objective scores such as PSNR or SSIM. Nevertheless, since the compression is performed in a very different way from traditional coding schemes such as HEVC, visual artifacts are also quite different and deserve to be subjectively assessed. In this paper, we propose a subjective quality assessment of SoftCast, pioneer and standard of the LVCT schemes. This study aims to better understand the trade-offs between the LVCT parameters that can be tuned to improve the quality. These parameters, including different GoP-sizes, Compression Ratios (CR) and Channel Signal-to-Noise Ratio (CSNR), are used to generate a dataset of 85 videos. A Double Stimulus Impairment Scale (DSIS) test is performed on the received videos to assess the perceived quality. Results show that the key characteristic of SoftCast, the linear relation between CSNR and PSNR, is also observed with the Mean-Opinion Scores (MOS), except at high CSNR where the quality saturates. In addition, Bjøntegaard model is used to quantify the trade-offs between CR, GoP-size and CSNR, depending on the intended application. Finally, the performance of objective metrics compared to the obtained MOS is evaluated. Results show that Multi-Scale SSIM (MS-SSIM), SSIM and Video Multimethod Assessment Fusion (VMAF) metrics offer the best correlation with the MOS values.

The latest video coding standards, H.264 and H.265, are highly vulnerable in error-prone networks. Reconstructed packets may exhibit significant degradation in terms of peak signal-to-noise ratio and visual quality. This paper presents a novel list-decoding approach exploiting the receiver side user datagram protocol (UDP) checksum. The proposed method identifies the possible locations of errors by analyzing the pattern of the calculated UDP checksum. This permits considerably reducing the number of candidate bitstreams in comparison to conventional list decoding approaches. When a packet composed of N bits contains a single-bit error, instead of considering N candidate bitstreams, as is the case in conventional list decoding approaches, the proposed approach considers N/32 candidate bitstreams, leading to a reduction of 97% of the number of candidates. For a two-bit error, the reduction increases to 99.6%. The method's performance is evaluated using H.264 and H.265 test model software. Our simulation results reveal that, on average, the error was corrected perfectly 80%-90% of the time (the original bitstream was recovered). In addition, the proposed approach provides, on average, a 2.79-dB gain over frame copy (FC) error concealment using the joint model and a 3.57-dB gain over our implementation of FC error concealment in the High Efficiency Video Coding test model.

This paper proposes a model to predict the energy consumption of a H.264/AVC intra-only based encoder designed for the wireless video sensor networks (WVSNs). Such model is of great interest in an energy-constrained context like the WVSN, where the video streams are processed prior to transmission. In fact, accounting for both processing's and transmission's consumed energies allows the optimization of the global energy consumption. The proposed model predicts the processing's energy consumption based on the considered Quantization Parameter (QP) and the Frame Rate (FR) values. The generic form of this model enables it to predict the energy consumption of any H.264/AVC intra-only based encoder. Simulation results demonstrate the accuracy of the proposed model, that is validated under different resolutions, QP and FR, with an average prediction error of 4%.

In this paper, we present an original image quality metric for open-loop transcoding architectures based on frequency selective transmission. The proposed metric computes the normalized HVS-weighted mean squared error (NWMSE) between the reference digital video compressed bitstream, and its transcoded version. This computation is performed directly from the quantized DCT coefficients of the compressed bitstream. The resulting MSE error is implicitly weighted by the HVS sensitivity by considering the MPEG perceptual coding properties. Finally, rate control and error propagation are also taken into account, in order to improve transcoded video quality assessment. Experimental results are given which show that the proposed NWMSE metric correlates well with a conventional WPSNR. This validates the proposed assumptions used for the NWMSE computation. The major advantage of the approach is its simplicity since it does not need to perform the complete decoding of the compressed bitstream. Hence, the NWMSE metric is highly suited for real-time video applications.

We propose a new postprocessing technique developed specifically for the reduction of color bleeding in DCT-coded color images. The proposed algorithm, based on a complete analysis of this particular kind of distortion, is used to identify and reduce color bleeding artifacts while attempting to preserve the sharpness of the reconstructed images. Simulation results show that the method successfully reduces color bleeding in reconstructed images and improves the visual quality, both objectively and subjectively.

One of the drawbacks of the discrete cosine transform (DCT) is visible block boundaries due to coarse quantization of the coefficients. In this paper, an algorithm for the reduction of blocking artifacts is presented. The proposed method allows to produce higher quality reconstructed images by adaptively filtering the video signal according to the noise visibility. A visual model is therefore defined for predicting the block edge visibility across each picture of the coded sequence. This model that accounts for the perceptual characteristics of the block distortion is described. Experimental results are presented for low bit-rate coded sequences. They show that the postfiltering operation yields significant results with enhanced visual quality.

The blocking effect is known to be the major degradation in block based video compression techniques. In this paper, we describe an adaptive postprocessing algorithm for the reduction of blocking effect in video coded sequences. It is based on a visual model for the prediction of blockiness visibility. The postfiltering operation is based on a 3D adaptive filter. A space-variant spatial filter is first used to smooth the pixels at block boundaries where the blocking effect is highly visible. It is followed by motion compensated nonlinear filtering in the temporal domain. Experimental results are presented showing that the proposed algorithm can remove the blocking effect while keeping image sharpness.