Marco Fumagalli

Multiple description video coding for scalable and robust transmission over IP

In this paper, we address the problem of video transmission over unreliable networks, such as the Internet, where packet losses occur. The most recent literature indicates multiple description (MD) as a promising coding approach to handle this issue. Moreover, it has been shown also how important the use of motion compensation prediction is in an MD-coding scheme. This paper proposes two architectures for multiple description video coding, both of them are based on the motion compensation prediction loop. The common characteristic of the two architectures is the use of a polyphase down-sampling technique to create the MDs and to introduce cross-redundancy among the descriptions. The first scheme, that we call drift-compensation multiple description video coder (DC-MDVC) appears very robust when used in an error-prone environment, but it can provide only two descriptions. The second architecture, called independent flow multiple description video coder (IF-MDVC), generates multiple sets of data before the motion compensation loop; in this case, there are no severe limitations in the selection of the number of descriptions used by the coder.

Polyphase down-sampling multiple-description coding for IP transmission

Recently the problem of transmitting data over heterogeneous networks has received considerable attention. Our specific interest is the communication of still images. In this work we present a Multiple Description system based on Polyphase DownSampling algorithm (PDMD) that splits an image source in an arbitrary number of balanced descriptions. Our goal is to obtain both the best reconstruction quality from the received descriptions (also only one) and a subjective indistinguishable reconstruction from the original, if all the descriptions are available.

Flexible redundancy insertion in a polyphase down sampling multiple description image coding

In this paper we address the problem of image transmission over unreliable networks. The system is based on multiple description coding, that introducing redundancy in the produced stream is able to guarantee a useful quality reconstruction also in presence of high percentage of packet losses. The target of this work is providing a flexible redundancy insertion in order to make the system robust for any packet loss situation over different networks (the Internet or mobile). The simulation results show the capability of the system to achieve the optimal image quality reconstruction according to network behavior.

A space domain approach for multiple description video coding

In this paper we address the problem of video transmission over unreliable networks using multiple description (MD) coding approach. Recent literature on MD techniques has shown the success of using motion compensation prediction scheme. Even though these MD systems have proved to be robust to error environment, they are forced to use only two descriptions. For this reason this paper proposes two architectures of MD video coders. The first, called DC-MDVC, is based on the classical MD video codec architecture and the principle contribution is the use of a new MD algorithm based on a spatial domain polyphase down-sampling technique. The second architecture, called IF-MDVC, proposes multi-level scalability generating a flexible number of descriptions. The results of both architectures are interesting and the second architecture, the subject of the current research, appears to perform impressively.

Video transmission over IP by using polyphase downsampling multiple description coding

Today the problem of transmitting data over heterogeneous networks has received considerable attention. In this paper we propose the design of a system to transmit in realtime high-quality video signal over Internet. To do that, we present a Multiple Description (MD) coding based on polyphase downsampling algorithm that splits an image source in an arbitrary number of balanced descriptions. Our goal is to obtain both the best reconstruction quality from the received descriptions (also only one) and a subjective indistinguishable reconstruction from the original, if all the descriptions are available.

Improved Bit Allocation in an Error-Resilient Scheme Based on Distributed Source Coding

In this work we propose an error-resilient scheme that allows enhancing the robustness of a video stream. Based on distributed source coding (DSC) principles, an auxiliary stream is sent in parallel to the main stream as a redundant representation of the sequence that is used to correct errors at the decoder, thus reducing the impact of drift. In order to perform an optimal bit allocation in the auxiliary stream, the encoder needs to compute a reliable estimate of the expected video distortion observed at the decoder side due to channel loss. This paper proposes an algorithm to calculate the expected distortion of decoded DCT-coefficients (dubbed EDDD) and its application to the bit allocation problem in a DSC based auxiliary stream

Estimation of erased data in a H.263 coded stream by using unbalanced multiple description coding

In this work we tackle the problem of error propagation that packet losses can cause in commonly used predictive video coding environments. Using unbalanced multiple description coding (UMDC) to generate redundant source data, we apply the consistency sequence estimation (CSE) algorithm for estimating the lost data. The CSE algorithm, proposed by Singh and Ortega for a 1-D input source signal in a DPCM context, uses a sequence search to verify the consistency of the estimates with the received data. The novelty of our work is the extension of the CSE algorithm to a block matching ME/MC video coder (such as H.263). To reach this aim we propose to work in the spatial domain. Among the advantages of the proposed error resilience scheme are its low-complexity and its compatibility with standard video coders.

Expected distortion of dct-coefficients in video streaming over unreliable channel

The Recursive Optimal per-Pixel Estimate (ROPE) algorithm allows the encoder to estimate the pixel-by-pixel expected distortion of the decoded video sequence due to channel loss. The algorithm requires in input an estimate of the packet loss rate and the knowledge of the error concealment technique used at the decoder with no need to perform any comparison between original and decoded frames. Although the ROPE algorithm computes the expected distortion in the pixel domain, in some applications it is important to have access to the expected distortion in the DCT domain, e.g., for an accurate allocation of the redundancy bits in error-resiliency schemes. This paper presents the extension of the ROPE algorithm in the transform DCT domain that allows estimating the expected distortion of the decoded video sequence for each DCT coefficient.

A Real-Time N-Descriptions Video Coding Architecture

In multiple description coding (MDC) literature two problems are still open: the capability of inserting any given amount of redundancy – in fact there is very often a minimum gap of redundancy under which it is impossible to go – and the opportunity to provide a high number of descriptions per frame – most of the architectures provide only two descriptions per frame. In this paper we focalize our attention on this second problem. A solution is to extend to N-descriptions the system given in [1], based on a polyphase down-sampler along rows and columns. Here multi-level scalability is introduced by generating the descriptions before the motion compensation loop. In this way there is no need of drift compensation terms and thus no structural constraints in scaling up the architecture.

A sequence-based error-concealment algorithm for an unbalanced multiple description video coding system

Video transmission over unreliable networks presents new challenges for research in video coding. In fact, in video coders that use predictive coding schemes, even a single packet loss may cause errors during the decoding process propagating in time. A way to increase the robustness of the coded stream and reduce the length of error propagation is the use of a multiple description coding (MDC) technique. The aim of this paper is to apply a novel sequence-based error-concealment (EC) algorithm to an unbalanced MD video coding system that generates both a high-quality (HQ) and a low-quality (LQ) description. In order to recover a loss in the current frames, the EC algorithm takes into account not only the spatial/temporal neighboring of the region the lost data correspond to, but also what is going to happen in a significant number of future frames looking both the HQ and the LQ descriptions. The sequence-based EC algorithm presents good performances when applied to video streams. The comparison with concurrent error-resilience techniques shows interesting results.