Pedro D. F. Correia

Multiple Description of Coded Video for Path Diversity Streaming Adaptation

This paper extends the current concept of multiple description coding (MDC) to the compressed domain, by proposing efficient splitting of standard single description coded (SDC) video into a multi-stream representation. A novel multiple description video splitting (MDVS) scheme is proposed to operate at network edges, for increased robustness in path diversity video streaming across heterogeneous communications chains. It is shown that poor performance of existing methods is mainly due to distortion accumulation, i.e., drift, when decoding is carried out with missing descriptions. The proposed scheme is able to effectively control drift distortion in both intra and inter predictive coding, even when only one description reaches the decoder. This is achieved by generating a controlled amount of relevant side information to compensate for drift accumulation, whenever any description is lost in its path. The simulation results show that any individual description can be decoded on its own without producing drift, achieving significant quality improvement at reduced redundancy cost. The overall performance evaluation, carried out by simulating video streaming over lossy networks with path diversity, also demonstrates that MDVS enables higher quality video in such heterogeneous networking environments, for a wide range of packet loss rates.

A method for improving the quality of mobile video under hard transcoding conditions

Mobile access to multimedia contents requires video transcoding functionality at the edge of the mobile network for interworking with heterogeneous networks and services. Under hard transcoding conditions, the bandwidth of a coded video stream needs to be drastically reduced such that the original temporal resolution cannot be maintained. Thus consecutive frame skipping is often unavoidable at the transcoder. We propose an efficient mechanism for improving the quality of service (QoS) delivered to the mobile user, by minimising consecutive frame skipping in transcoding systems. The simulation results show that a better signal quality is obtained at the receiver during hard transcoding periods.

Drift-free multiple description intra video coding

This paper proposes a multiple description coding scheme based on a multi-loop structure, which prevents drift distortion accumulation in intra predicted slices. The drift is compensated by generating a controlled amount of side information used by the decoder whenever any description is lost in the corresponding network path. The experimental results show that intra predicted slices do not suffer from drift and their quality is significantly improved (e.g., 6-8 dB) at reduced redundancy cost, (e.g., 0.2-0.25), in comparison with the open loop implementation. Error propagation in subsequent frames is also evaluated when one description is lost for a whole frame and for two rows of macroblocks. In both cases the overall video quality is significantly improved and considering normal GOP sizes the redundancy introduced by the proposed scheme is negligible.

Robust decoding of MDC depth maps for enhanced 3D video over hybrid broadcasting networks

This paper addresses the problem of robust decoding of 3D video over hybrid broadcast networks, using Multiple Description Coding (MDC). Despite the fact that MDC allows decoding of any description even when the others are lost in the multipath network, the resulting coarsely decoded depth maps produce unacceptable distortion in synthesised views. This is particularly harmful in the case of intra-coded depth slices because of subsequent error propagation. To achieve improved quality in the virtual views synthesised from MDC depth maps received with lost descriptions, a method is proposed based on the depth geometric information extracted from the received descriptions and also from texture motion. Accurate recovery of either lost or coarsely decoded depth slices from one single description, is achieved by jointly using motion information, depth map edges and spatially neighbouring depth values. Comparing with MDC decoding without enhanced reconstruction of lost descriptions, the proposed method reaches quality gains up to 2.29dB for loss rates of 10%.

Rate control for unbalanced multiple description video streaming

Unbalanced multiple description coding (U-MDC) of video signals aims to obtain different coding rates for transmission over channels with asymmetric available bandwidth. This paper proposes a new rate control method, based on Multiple Description Scalar Quantisation (MDSQ), to generate unbalanced descriptions for asymmetric multipath video streaming. A new set of index assignment tables combined with an extension of the @r model is devised to generate two unbalanced descriptions with controlled rate, using U-MDC under the general coding framework of H.264/AVC. This work demonstrates that a linear relationship between the rate and percentage of zeros in the transform coefficients of each description is maintained across different description domains, i.e., when moving from the single description domain (SDC) into the MDC domain. The simulation results show that rate-distortion performance of U-MDC is better than its equivalent balanced MDC. The proposed rate control algorithm exhibits high accuracy in achieving different target bitrates and unbalanced ratios between two descriptions. Improved performance is also achieved in video streaming over asymmetric transmission paths, where each description rate can be adapted according to different channel conditions.

Optimal priority MDC video streaming for networks with path diversity

This paper proposes a robust video streaming scheme for priority networks with path diversity, based on a combined approach of multiple description coding (MDC) with optimal picture classification into two priorities. A binary classification algorithm is proposed to define high (HP) and low (LP) priority network abstraction layer units (NALU), which in turn define the packet priorities. An optimisation algorithm is used to find HP pictures, based on dynamic programming and relying on minimisation of the packet loss concealment distortion. The paper shows that the proposed algorithm is able to effectively improve the decoded video without increasing the MDC stream redundancy. The overall performance evaluation, carried out by simulating MDC video streaming over lossy networks with path diversity, demonstrates that the proposed algorithm yields higher video quality for a wide range of packet loss rates (PLR). Comparing with no-priority MDC video streaming schemes, the simulation results show that the proposed algorithm can improve the average PSNR results in 0.7-3.2dB for packet loss rates between 3% and 15%.

Enhanced H.264/AVC video streaming using network-adaptive multiple description coding

This paper presents a network-adaptive multiple description coding (MDC) method for enhanced video streaming over multipath channels. The novel feature of the proposed MDC network adaptation scheme is the generation of a controlled amount of side information to compensate for drift distortion due to packet loss. This yields higher robustness of multiple description (MD) H.264/AVC streams than single description (SD) ones. Multiple Description Scalar Quantisation (MDSQ) is used to split an SD video stream in two complementary streams (two descriptions) for transmission over a multipath channel. The simulation results show that significantly better quality is achieved by using the proposed scheme instead of either SDC streams or classic SDC-MDSQ network adaptation without side information.

Multiple description video transcoding with temporal drift control

This paper proposes a multiple description (MD) transcoding scheme capable of preventing drift by distortion accumulation in temporally predicted motion compensated slices. Drift compensation is achieved by generating a controlled amount of side information to be used for decoding whenever a description fails to reach the end user terminal. The side information is generated by re-encoding the transcoding residue with an independent quantisation parameter which also controls redundancy. A simplified architecture is devised to reduce transcoding complexity in regard to the number of processing functions and buffer requirements. The experimental results show that temporally predicted frames do not suffer from drift and their quality is significantly improved at reduced redundancy cost in comparison with a classic MD transcoding scheme.

Enhancement method for multiple description decoding of depth maps subject to random loss

This paper proposes a method to improve the quality of depth maps transmitted in multiple descriptions through multipath error prone networks. Whenever a single description is lost, the remaining ones are still able to provide a coarsely decoded version of the depth map. While in multiple description video, such coarse decoding is still acceptable for display, in the case of depth maps the additional decoding distortion propagates through the corresponding view synthesis. The proposed method is capable of enhancing low quality depth maps decoded from one single description, based on geometric information available in coarsely decoded slices, combined with higher quality depth values in adjacent slices decoded from both descriptions. In comparison with existing MDC decoders, the enhancement method achieves quality gains in synthesised views up to 1.69dB for packet loss rates of 10%.

Multiple Description Video Streaming over Asymmetric Channels

This paper proposes an efficient Unbalanced Multiple Description Scalar Quantisation (U-MDSQ) method for video streaming over asymmetric channels. In order to control the asymmetric target rates for each coded descriptions, the UMDSQ parameters are combined with the rate control method based on the existing linear relationship between rate and percentage of zeros in transform coefficients in MDSQ domain. The simulation results show that the proposed method exhibits high accuracy for a wide range of target bitrates and unbalanced rates between descriptions. Moreover, the obtained results show the effectiveness of the proposed method in order to improve the overall performance over channels with asymmetric rate and packet loss rate (PLR) conditions, when compared with Balanced MDSQ. This method finds application in video streaming with path diversity based on Multiple Description Coding (MDC) with dynamic channel conditions.