J. De Cock

Architectures for Fast Transcoding of H.264/AVC to Quality-Scalable SVC Streams

The scalable extension of H.264/AVC (SVC) was recently standardized, and offers scalability at a minor penalty in rate-distortion efficiency when compared to single-layer H.264/AVC coding. In SVC, a scaled version of the original video sequence can easily be extracted by dropping layers from the stream. However, most of the video content nowadays is still produced in a single-layer format. While decoding and reencoding is a possible solution to introduce scalability in the existing bitstreams, this is an approach which requires a tremendous amount of time and effort. In this paper, we show that transcoding can be used to intelligently derive scalable bitstreams from existing single-layer streams. We focus on SNR scalability, and introduce techniques that are able to create multiple quality layers in the bitstreams. We also discuss bitstream rewriting from SVC to H.264/AVC, and examine how our newly proposed architectures can benefit from the changes that were introduced for bitstream rewriting. Architectures with different rate distribution flexibility and computational complexity are discussed. Rate-distortion performance of transcoding is shown to be comparable to that of reencoding at a fraction of the time needed for the latter.

End-To-End Security for Video Distribution: The Combination of Encryption, Watermarking, and Video Adaptation

This article introduces the reader to the relevant techniques that are needed to implement such an end-to-end commutative security system for video distribution and presents a practical solution for encryption and watermarking compliant with H.264/Advanced Video Coding (AVC) and the upcoming High Efficiency Video Coding (HEVC) video coding standards. To minimize the overhead and visual impact, a practical tradeoff between the security of the encryption routine, robust watermarking, and transcoding possibilities is investigated. We demonstrate that our combined commutative protection system effectively scrambles video streams, achieving structural similarity index (SSIM) values below 0.2 across a range of practical bit rates, while allowing robust watermarking and transcoding.

No-Reference Bitstream-Based Visual Quality Impairment Detection for High Definition H.264/AVC Encoded Video Sequences

Ensuring and maintaining adequate Quality of Experience towards end-users are key objectives for video service providers, not only for increasing customer satisfaction but also as service differentiator. However, in the case of High Definition video streaming over IP-based networks, network impairments such as packet loss can severely degrade the perceived visual quality. Several standard organizations have established a minimum set of performance objectives which should be achieved for obtaining satisfactory quality. Therefore, video service providers should continuously monitor the network and the quality of the received video streams in order to detect visual degradations. Objective video quality metrics enable automatic measurement of perceived quality. Unfortunately, the most reliable metrics require access to both the original and the received video streams which makes them inappropriate for real-time monitoring. In this article, we present a novel no-reference bitstream-based visual quality impairment detector which enables real-time detection of visual degradations caused by network impairments. By only incorporating information extracted from the encoded bitstream, network impairments are classified as visible or invisible to the end-user. Our results show that impairment visibility can be classified with a high accuracy which enables real-time validation of the existing performance objectives.

3D video compression based on high efficiency video coding

With the advent of autostereoscopic displays, questions rise on how to efficiently compress the video information needed by such displays. Additionally, for gradual market acceptance of this new technology it is valuable to have a solution offering forward compatibility with stereo 3D video as it is used nowadays. In this paper, a multiview compression scheme making use of the efficient single-view coding tools used in High Efficiency Video Coding (HEVC) is provided. Although efficient single view compression can be obtained with HEVC, a multiview adaptation of this standard under development is proposed, offering additional coding gains. On average, for the texture information, the total bitrate can be reduced by 37.2% compared to simulcast HEVC. For depth map compression, gains largely depend on the quality of the captured content. Additionally, a forward compatible solution is proposed offering the possibility for a gradual upgrade from H.264/AVC based stereoscopic 3D systems to an HEVC-based autostereoscopic environment. With the proposed system, significant rate savings compared to Multiview Video Coding (MVC) are presented.

A novel hybrid requantization transcoding scheme for H.264/AVC

Transcoding is a fast and elegant solution for the adaptation of video content. In the case of bitrate adaptation, an important technique is requantization transcoding. In this paper, we extend our previous work, that focused on requantization of intra-coded pictures, to P and B pictures. We show that by using a combination of techniques, depending on the slice and macroblock type, improved results are obtained when compared to previously existent architectures. We also show that in the important case of transcoding to low bitrates, results of this hybrid architecture approximate the rate-distortion performance of the computationally complex decoder-encoder cascade.

Efficient Low-Delay Distributed Video Coding

Distributed video coding (DVC) is a video coding paradigm that allows for a low-complexity encoding process by exploiting the temporal redundancies in a video sequence at the decoder side. State-of-the-art DVC systems exhibit a structural coding delay since exploiting the temporal redundancies through motion-compensated interpolation requires the frames to be decoded out of order. To alleviate this problem, we propose a system based on motion-compensated extrapolation that allows for efficient low-delay video coding with low complexity at the encoder. The proposed extrapolation technique first estimates the motion field between the two most recently decoded frames using the Lucas-Kanade algorithm. The obtained motion field is then extrapolated to the current frame using an extrapolation grid. The proposed techniques are implemented into a novel architecture featuring hybrid block-frequency Wyner-Ziv coding as well as mode decision. Results show that having references from both temporal directions in interpolation provides superior rate-distortion performance over a single temporal direction in extrapolation, as expected. However, the proposed extrapolation method is particularly suitable for low-delay coding as it performs better than H.264/AVC intra, and it is even able to outperform the interpolation-based DVC codec from DISCOVER for several sequences.

Efficient spatial resolution reduction transcoding for H.264/AVC

In this paper, we present a spatial resolution reduction transcoding architecture for H.264/AVC, which extends open-loop transcoding with a low-complexity compensation technique in the reduced-resolution domain. The proposed architecture removes visual artifacts from the transcoded sequence, while keeping complexity significantly lower than more traditional cascaded decoder-encoder architectures. The refinement step of the proposed architecture can be used to further improve rate-distortion performance, at the cost of additional complexity. In this way, a dynamic-complexity transcoder is rendered possible.

Advanced bitstream rewriting from H.264/AVC to SVC

In previous work, we introduced an H.264/AVC-to-SVC transcoder for creating SVC streams with multiple quality layers from a single-layer H.264/AVC stream. This architecture was able to restrain the error drift due to requantization of the residual coefficients. In this paper, we show that it is possible to further reduce the complexity, and completely eliminate the drift in the enhancement layer, by making use of the bitstream rewriting functionality in SVC. We propose different novel architectures, which are able to flexibly distribute the data among the different created layers.

Fast Channel Switching Based on SVC in IPTV Environments

In Internet Protocol TeleVision (IPTV) systems, the use of video compression results in a trade-off between random access and bandwidth consumption. Most of the time, priority is given to compression efficiency, resulting in low channel switching performance. In this paper, a Scalable Video Coding (SVC) configuration is proposed, wherein base and enhancement layer are coded in such a way that fast channel switching can be offered without impacting the access network bandwidth consumption. This is achieved by encoding a full quality slow channel switching version of the video stream in the base layer extended with a reduced quality fast switching enhancement layer. Additionally, this configuration offers backward compatibility with H.264/AVC, enabling a gradual upgrade of the IPTV system from H.264/AVC to SVC. When comparing this technique to single layer H.264/AVC, 25.0% bandwidth reduction on the access network is obtained without impacting channel switching speed, but only at the cost of a slightly reduced quality ( -1 dB PSNR) during a short transition period (maximum 48 frames). If a comparison is made with a regular SVC configuration, 39.4% bandwidth reduction on the access network during steady state is obtained. Compared to simulcast H.264/AVC, 32.0% bandwidth reduction on the core network is observed.

Fast quadtree level decision algorithm for H.264/HEVC transcoder

The High Efficiency Video Coding (HEVC) was developed by the Joint Collaborative Team on Video Coding (JCT-VC) to replace the current H.264/AVC standard which has been widely adopted in the last years. Therefore, there is a lot of legacy content encoded with H.264/AVC and an efficient conversion to HEVC is needed. This paper, presents a Fast Quadtree Level Decision (FQLD) algorithm that greatly reduces the complexity of the transcoding process between H.264/AVC and HEVC. The proposal tries to exploit the information gathered at the H.264/AVC decoder to make decisions on Coding Units (CU) splitting in HEVC using a Naïve-Bayes (NB) probabilistic classifier. Experimental results show that the proposed transcoder can achieve a good tradeoff between coding efficiency and complexity.