Survey of Error Concealment techniques: Research directions and open issues

© 2015 IEEE. Error Concealment (EC) techniques use either spatial, temporal or a combination of both types of information to recover the data lost in transmitted video. In this paper, existing EC techniques are reviewed, which are divided into three categories, namely Intra-frame EC, Inter-frame EC, and Hybrid EC techniques. We first focus on the EC techniques developed for the H.264/AVC standard. The advantages and disadvantages of these EC techniques are summarized with respect to the features in H.264. Then, the EC algorithms are also analyzed. These EC algorithms have been recently adopted in the newly introduced H.265/HEVC standard. A performance comparison between the classic EC techniques developed for H.264 and H.265 is performed in terms of the average PSNR. Lastly, open issues in the EC domain are addressed for future research consideration

Error resilience and concealment techniques for high-efficiency video coding

This thesis investigates the problem of robust coding and error concealment in High Efficiency Video Coding (HEVC). After a review of the current state of the art, a simulation study about error robustness, revealed that the HEVC has weak protection against network losses with significant impact on video quality degradation. Based on this evidence, the first contribution of this work is a new method to reduce the temporal dependencies between motion vectors, by improving the decoded video quality without compromising the compression efficiency. The second contribution of this thesis is a two-stage approach for reducing the mismatch of temporal predictions in case of video streams received with errors or lost data. At the encoding stage, the reference pictures are dynamically distributed based on a constrained Lagrangian rate-distortion optimization to reduce the number of predictions from a single reference. At the streaming stage, a prioritization algorithm, based on spatial dependencies, selects a reduced set of motion vectors to be transmitted, as side information, to reduce mismatched motion predictions at the decoder. The problem of error concealment-aware video coding is also investigated to enhance the overall error robustness. A new approach based on scalable coding and optimally error concealment selection is proposed, where the optimal error concealment modes are found by simulating transmission losses, followed by a saliency-weighted optimisation. Moreover, recovery residual information is encoded using a rate-controlled enhancement layer. Both are transmitted to the decoder to be used in case of data loss. Finally, an adaptive error resilience scheme is proposed to dynamically predict the video stream that achieves the highest decoded quality for a particular loss case. A neural network selects among the various video streams, encoded with different levels of compression efficiency and error protection, based on information from the video signal, the coded stream and the transmission network. Overall, the new robust video coding methods investigated in this thesis yield consistent quality gains in comparison with other existing methods and also the ones implemented in the HEVC reference software. Furthermore, the trade-off between coding efficiency and error robustness is also better in the proposed methods

Reference picture selection using checkerboard pattern for resilient video coding

The improved compression efficiency achieved by the High Efficiency Video Coding (HEVC) standard has the counter-effect of decreasing error resilience in transmission over error-prone channels. To increase the error resilience of HEVC streams, this paper proposes a checkerboard reference picture selection method in order to reduce the prediction mismatch at the decoder in case of frame losses. The proposed approach not only allows to reduce the error propagation at the decoder, but also enhances the quality of reconstructed frames by selectively constraining the choice of reference pictures used for temporal prediction. The underlying approach is to increase the amount of accurate temporal information at the decoder when transmission errors occur, to improve the video quality by using an efficient combination of diverse motion fields. The proposed method compensates for the small loss of coding efficiency at frame loss rates as low as 3%. For a single frame-loss event the proposed method can achieve up to 2 dB of gain in the affected frames and an average quality gain of 0:84 dB for different error prone conditions

Intra Coding Strategy for Video Error Resiliency: Behavioral Analysis

One challenge in video transmission is to deal with packet loss. Since the compressed video streams are sensitive to data loss, the error resiliency of the encoded video becomes important. When video data is lost and retransmission is not possible, the missed data should be concealed. But loss concealment causes distortion in the lossy frame which also propagates into the next frames even if their data are received correctly. One promising solution to mitigate this error propagation is intra coding. There are three approaches for intra coding: intra coding of a number of blocks selected randomly or regularly, intra coding of some specific blocks selected by an appropriate cost function, or intra coding of a whole frame. But Intra coding reduces the compression ratio; therefore, there exists a trade-off between bitrate and error resiliency achieved by intra coding. In this paper, we study and show the best strategy for getting the best rate-distortion performance. Considering the error propagation, an objective function is formulated, and with some approximations, this objective function is simplified and solved. The solution demonstrates that periodical I-frame coding is preferred over coding only a number of blocks as intra mode in P-frames. Through examination of various test sequences, it is shown that the best intra frame period depends on the coding bitrate as well as the packet loss rate. We then propose a scheme to estimate this period from curve fitting of the experimental results, and show that our proposed scheme outperforms other methods of intra coding especially for higher loss rates and coding bitrates

Reference picture selection using checkerboard pattern for resilient video coding

The improved compression efficiency achieved by the High Efficiency Video Coding (HEVC) standard has the counter-effect of decreasing error resilience in transmission over error-prone channels. To increase the error resilience of HEVC streams, this paper proposes a checkerboard reference picture selection method in order to reduce the prediction mismatch at the decoder in case of frame losses. The proposed approach not only allows to reduce the error propagation at the decoder, but also enhances the quality of reconstructed frames by selectively constraining the choice of reference pictures used for temporal prediction. The underlying approach is to increase the amount of accurate temporal information at the decoder when transmission errors occur, to improve the video quality by using an efficient combination of diverse motion fields. The proposed method compensates for the small loss of coding efficiency at frame loss rates as low as 3%. For a single frame-loss event the proposed method can achieve up to 2 dB of gain in the affected frames and an average quality gain of 0:84 dB for different error prone conditions

Enhanced quality reconstruction of erroneous video streams using packet filtering based on non-desynchronizing bits and UDP checksum-filtered list decoding

The latest video coding standards, such as H.264 and H.265, are extremely vulnerable in error-prone networks. Due to their sophisticated spatial and temporal prediction tools, the effect of an error is not limited to the erroneous area but it can easily propagate spatially to the neighboring blocks and temporally to the following frames. Thus, reconstructed video packets at the decoder side may exhibit significant visual quality degradation. Error concealment and error corrections are two mechanisms that have been developed to improve the quality of reconstructed frames in the presence of errors. In most existing error concealment approaches, the corrupted packets are ignored and only the correctly received information of the surrounding areas (spatially and/or temporally) is used to recover the erroneous area. This is due to the fact that there is no perfect error detection mechanism to identify correctly received blocks within a corrupted packet, and moreover because of the desynchronization problem caused by the transmission errors on the variable-length code (VLC). But, as many studies have shown, the corrupted packets may contain valuable information that can be used to reconstruct adequately of the lost area (e.g. when the error is located at the end of a slice). On the other hand, error correction approaches, such as list decoding, exploit the corrupted packets to generate several candidate transmitted packets from the corrupted received packet. They then select, among these candidates, the one with the highest likelihood of being the transmitted packet based on the available soft information (e.g. log-likelihood ratio (LLR) of each bit). However, list decoding approaches suffer from a large solution space of candidate transmitted packets. This is worsened when the soft information is not available at the application layer; a more realistic scenario in practice. Indeed, since it is unknown which bits have higher probabilities of having been modified during transmission, the candidate received packets cannot be ranked by likelihood. In this thesis, we propose various strategies to improve the quality of reconstructed packets which have been lightly damaged during transmission (e.g. at most a single error per packet). We first propose a simple but efficient mechanism to filter damaged packets in order to retain those likely to lead to a very good reconstruction and discard the others. This method can be used as a complement to most existing concealment approaches to enhance their performance. The method is based on the novel concept of non-desynchronizing bits (NDBs) defined, in the context of an H.264 context-adaptive variable-length coding (CAVLC) coded sequence, as a bit whose inversion does not cause desynchronization at the bitstream level nor changes the number of decoded macroblocks. We establish that, on typical coded bitstreams, the NDBs constitute about a one-third (about 30%) of a bitstream, and that the effect on visual quality of flipping one of them in a packet is mostly insignificant. In most cases (90%), the quality of the reconstructed packet when modifying an individual NDB is almost the same as the intact one. We thus demonstrate that keeping, under certain conditions, a corrupted packet as a candidate for the lost area can provide better visual quality compared to the concealment approaches. We finally propose a non-desync-based decoding framework, which retains a corrupted packet, under the condition of not causing desynchronization and not altering the number of expected macroblocks. The framework can be combined with most current concealment approaches. The proposed approach is compared to the frame copy (FC) concealment of Joint Model (JM) software (JM-FC) and a state-of-the-art concealment approach using the spatiotemporal boundary matching algorithm (STBMA) mechanism, in the case of one bit in error, and on average, respectively, provides 3.5 dB and 1.42 dB gain over them. We then propose a novel list decoding approach called checksum-filtered list decoding (CFLD) which can correct a packet at the bit stream level by exploiting the receiver side user datagram protocol (UDP) checksum value. The proposed approach is able to identify the possible locations of errors by analyzing the pattern of the calculated UDP checksum on the corrupted packet. This makes it possible to considerably reduce the number of candidate transmitted packets in comparison to conventional list decoding approaches, especially when no soft information is available. When a packet composed of N bits contains a single bit in error, instead of considering N candidate packets, as is the case in conventional list decoding approaches, the proposed approach considers approximately N/32 candidate packets, leading to a 97% reduction in the number of candidates. This reduction can increase to 99.6% in the case of a two-bit error. The method’s performance is evaluated using H.264 and high efficiency video coding (HEVC) test model software. We show that, in the case H.264 coded sequence, on average, the CFLD approach is able to correct the packet 66% of the time. It also offers a 2.74 dB gain over JM-FC and 1.14 dB and 1.42 dB gains over STBMA and hard output maximum likelihood decoding (HO-MLD), respectively. Additionally, in the case of HEVC, the CFLD approach corrects the corrupted packet 91% of the time, and offers 2.35 dB and 4.97 dB gains over our implementation of FC concealment in HEVC test model software (HM-FC) in class B (1920×1080) and C (832×480) sequences, respectively

Keyframe insertion : enabling low-latency random access and packet loss repair

From a video coding perspective, there are two challenges when performing live video distribution over error-prone networks, such as wireless networks: random access and packet loss repair. There is a scarceness of solutions that do not impact steady-state usage and users with reliable connections. The proposed solution minimizes this impact by complementing a compression-efficient video stream with a companion stream solely consisting of keyframes. Although the core idea is not new, this paper is the first work to provide restrictions and modifications necessary to make this idea work using the High-Efficiency Video Coding (H.265/HEVC) compression standard. Additionally, through thorough quantification, insight is provided on how to provide low-latency fast channel switching capabilities and error recovery at low quality impact, i.e., less than 0.94 average Video Multimethod Assessment Fusion (VMAF) score decrease. Finally, worst-case drift artifacts are described and visualized such that the reader gets an overall picture of using the keyframe insertion technique

Error control strategies in H.265|HEVC video transmission

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonWith the rapid development in video coding technologies in the last decade, high-resolution video delivery suffers from packet loss due to unreliable transmission channels (time-varying characteristics). The error Resilience approaches at channel coding level are less efficient to implement in real time video transmission as the encoded video samples are in variable code length. Therefore, error resilience in video coding standard plays a vital role to reduce the effect of error propagation and improve the perceived visual quality. The main work in this thesis is to develop an efficient error resilience mechanism for H.265|HEVC video coding standard to reduce the effects of error propagation in error-prone conditions. In this thesis, two error resilience algorithms are proposed. The first one is Adaptive Slice Encoding (ASE) error resilience algorithm. The concept of this algorithm is to extract and protect the most active slices in the coded bitstream based on the adaptive search window. This algorithm can be applied in low delay video transmission with and without using a feedback channel. It is also designed to be compatible with reference coding software manual (HM16) for H.265|HEVC coding standard. The second proposed algorithm is a joint encoder-decoder error resilience called Error resilience based on Supplemental Enhancement Information (ERSEI) algorithm. A feedback message status is used from the decoder to notify the encoder to start encoding clean random-access picture adaptively based on the decoded picture hash message status from the decoder. At the same time, the decoder will be notified to start the error concealment process whilst waiting to receive correct video data. A recovery point message from the decoder feedback channel is used to update the encoder with error messages. In this thesis, extensive experimental work, evaluation, and comparison with state-of-the-art related algorithms have been conducted to evaluate the proposed algorithms. Furthermore, the best trade-off between the coding efficiency of the proposed error resilience algorithms and error resilience performance has been considered at the design stage. The experimental work evaluation includes both encoding conditions, i.e. error-free and error-prone. The results achieved from the experiments show significant improvements, in (Y-PSNR) results and subjective quality of the decoded bitstream, using the proposed algorithm in error-prone conditions with a variety of packet loss rates. Moreover, experimental work is conducted to test the algorithms complexity in terms of required processing execution time at both encoding and decoding stages. Additionally, the video coding standard performance for both H.264|AVC and H.265|HEVC coding standards are evaluated in error-free and error-prone environments. For ASE algorithm and when compared with improved region of interest (IROI) and region of interest (ROI) algorithms, a significant improvement in visual quality was the most obvious finding from the obtained results with PLRs of 2-18 (%). For ERSEI algorithm and when compared with the default HM16 with pixel copy concealment and motion compensated error concealment (MCEC) techniques, the evaluation results indicate clear visual quality enhancement under different packet loss rates PLRs (1,2 6, 8) %.The Ministry of Higher Education and Scientific Research in Ira