A maximum likelihood approach to video error correction applied to H.264 decoding

Video error concealment has long been identified as the last line of defense against transmission errors. This is especially true for real time video communication systems where retransmissions are rarely used because of timing constraints. Since error handling is outside the scope of video coding standards, decoders may choose to simply ignore the corrupted packets, or attempt to decode their content. Video error correction is a viable alternative to deal with transmission errors when corrupted packets reach their destination. Until now, these approaches have received little considerations. This is mainly because the proposed methods either rely on specific coding tools or constraints, or require far too many computations compared to video error concealment techniques. In this thesis, we propose a novel video error correction method based on maximum likelihood decoding. The method estimates the likeliest syntactically valid video slice content based on the erroneous video packets rather than discarding the content, and concealing the missing information. Such content is obtained by combining the likelihood of the candidate codewords with the bit modification likelihood associated to each candidate. We propose two solutions centered around our maximum likelihood decoding approach. First, we introduce a slice-level video error correction method. Furthermore, we show how to integrate the soft-output information shared by the channel decoder to evaluate the bit modification likelihood. We also show that it is possible to use our maximum likelihood decoding approach when soft-output information is not available. Then, we refine the solution at the syntax-element-level. The final solution we obtain can be used in real-time communication systems as it is computationally inexpensive compared to the slice-level solution, or the solutions proposed in the literature. Our final solution is then applied to the correction of videos conforming to the H.264 Baseline profile. We selected three 720x480 sequences, five 704x576 sequences, and one 720x576 sequence to run simulations. Each sequence was coded at a target bitrate of 1 Mbps, 1.2 Mbps, and 1.5 Mbps. All 27 sequences were then submitted to a noisy channel with a bit error rate ranging from 10−5 to 10−3. Our 5400 observations show a PSNR improvement of 1.69 dB over the video error concealment method implemented in the H.264 reference software. Furthermore, our results also indicate a 0.42 dB PSNR improvement over state-of-the-art error concealment STBMA+PDE

A unary error correction code for the near-capacity joint source and channel coding of symbol values from an infinite set

A novel Joint Source and Channel Code (JSCC) is proposed, which we refer to as the Unary Error Correction (UEC) code. Unlike existing JSCCs, our UEC facilitates the practical encoding of symbol values that are selected from a set having an infinite cardinality. Conventionally, these symbols are conveyed using Separate Source and Channel Codes (SSCCs), but we demonstrate that the residual redundancy that is retained following source coding results in a capacity loss, which is found to have a value of 1.11 dB in a particular practical scenario. By contrast, the proposed UEC code can eliminate this capacity loss, or reduce it to an infinitesimally small value. Furthermore, the UEC code has only a moderate complexity, facilitating its employment in practical low-complexity applications

Rateless Codes with Progressive Recovery for Layered Multimedia Delivery

This paper proposes a novel approach, based on unequal error protection, to enhance rateless codes with progressive recovery for layered multimedia delivery. With a parallel encoding structure, the proposed Progressive Rateless codes (PRC) assign unequal redundancy to each layer in accordance with their importance. Each output symbol contains information from all layers, and thus the stream layers can be recovered progressively at the expected received ratios of output symbols. Furthermore, the dependency between layers is naturally considered. The performance of the PRC is evaluated and compared with some related UEP approaches. Results show that our PRC approach provides better recovery performance with lower overhead both theoretically and numerically

Extrinsic information modification in the turbo decoder by exploiting source redundancies for HEVC video transmitted over a mobile channel

An iterative turbo decoder-based cross layer error recovery scheme for compressed video is presented in this paper. The soft information exchanged between two convolutional decoders is reinforced both by channel coded parity and video compression syntactical information. An algorithm to identify the video frame boundaries in corrupted compressed sequences is formulated. This paper continues to propose algorithms to deduce the correct values for selected fields in the compressed stream. Modifying the turbo extrinsic information using these corrections acts as reinforcements in the turbo decoding iterative process. The optimal number of turbo iterations suitable for the proposed system model is derived using EXIT charts. Simulation results reveal that a transmission power saving of 2.28% can be achieved using the proposed methodology. Contrary to typical joint cross layer decoding schemes, the additional resource requirement is minimal, since the proposed decoding cycle does not involve the decompression function

Distributed video coding for wireless video sensor networks: a review of the state-of-the-art architectures

Distributed video coding (DVC) is a relatively new video coding architecture originated from two fundamental theorems namely, Slepian–Wolf and Wyner–Ziv. Recent research developments have made DVC attractive for applications in the emerging domain of wireless video sensor networks (WVSNs). This paper reviews the state-of-the-art DVC architectures with a focus on understanding their opportunities and gaps in addressing the operational requirements and application needs of WVSNs

A Two-Stage Decoder for Pragmatic Trellis-Coded M-PSK Modulation Using a Symbol Transformation

A two-stage decoding procedure for pragmatic trellis-coded modulation (TCM) is introduced. It applies a transformation from the received I-channel and Q-channel samples onto points in a two-dimensional (2-D) signal space that contains a coset constellation. For pragmatic TCM over M-PSK signal sets with ν coded bits per symbol, ν=1, 2, the signal points in the coset constellations represent cosets of a B/QPSK signal subset-associated with the coded bits-in the original M-PSK signal constellation. A conventional Viterbi decoder operates on the transformed symbols to estimate the coded bits. After reencoding these bits, the uncoded bits are estimated in a second stage, on a symbol-by-symbol basis, with decisions based on the location of the received symbols. In addition to requiring no changes in the Viterbi decoder core, it is shown that the proposed method results in savings of up to 40% in the memory required to store (or in the size of the logic required to compute) metrics and transformed symbols

Joint source-channel coding/decoding of 3D-ESCOT bitstreams

International audienceJoint source-channel decoding (JSCD) exploits residual redundancy in compressed bitstreams to improve the robustness to transmission errors of multimedia coding schemes. This paper proposes an architecture to introduce some additional side information in compressed streams to help JSCD. This architecture exploits a reference decoder already present or introduced at the encoder side. An application to the robust decoding of 3D-ESCOT encoded bitstreams generated within the Vidwav video coder is presented. The layered bitstream generated by this encoder allows SNR scalability, and moreover, when processed by a JSCD, provides increased robustness to transmission errors compared with a single layered bitstream

Expanding window fountain codes for unequal error protection

A novel approach to provide unequal error protection (UEP) using rateless codes over erasure channels, named Expanding Window Fountain (EWF) codes, is developed and discussed. EWF codes use a windowing technique rather than a weighted (non-uniform) selection of input symbols to achieve UEP property. The windowing approach introduces additional parameters in the UEP rateless code design, making it more general and flexible than the weighted approach. Furthermore, the windowing approach provides better performance of UEP scheme, which is confirmed both theoretically and experimentally. © 2009 IEEE