A rate control algorithm for scalable video coding

This thesis proposes a rate control (RC) algorithm for H.264/scalable video coding (SVC) specially designed for real-time variable bit rate (VBR) applications with buffer constraints. The VBR controller assumes that consecutive pictures within the same scene often exhibit similar degrees of complexity, and aims to prevent unnecessary quantization parameter (QP) fluctuations by allowing for just an incremental variation of QP with respect to that of the previous picture. In order to adapt this idea to H.264/SVC, a rate controller is located at each dependency layer (spatial or coarse grain scalability) so that each rate controller is responsible for determining the proper QP increment. Actually, one of the main contributions of the thesis is a QP increment regression model that is based on Gaussian processes. This model has been derived from some observations drawn from a discrete set of representative encoding states. Two real-time application scenarios were simulated to assess the performance of the VBR controller with respect to two well-known RC methods. The experimental results show that our proposal achieves an excellent performance in terms of quality consistency, buffer control, adjustment to the target bit rate, and computational complexity. Moreover, unlike typical RC algorithms for SVC that only satisfy the hypothetical reference decoder (HRD) constraints for the highest temporal resolution sub-stream of each dependency layer, the proposed VBR controller also delivers HRD-compliant sub-streams with lower temporal resolutions.To this end, a novel approach that uses a set of buffers (one per temporal resolution sub-stream) within a dependency layer has been built on top of the RC algorithm.The proposed approach aims to simultaneously control the buffer levels for overflow and underflow prevention, while maximizing the reconstructed video quality of the corresponding sub-streams. This in-layer multibuffer framework for rate-controlled SVC does not require additional dependency layers to deliver different HRD-compliant temporal resolutions for a given video source, thus improving the coding e ciency when compared to typical SVC encoder con gurations since, for the same target bit rate, less layers are encoded

Colección de prácticas de tratamiento digital de audio para telecomunicaciones

Grado en Ingeniería de Sistemas Audiovisuales. Asignatura: Tratamiento digital de audio para Telecomunicacione

In-layer multi-buffer framework for rate-controlled scalable video coding

Temporal scalability is supported in scalable video coding (SVC) by means of hierarchical prediction structures, where the higher layers can be ignored for frame rate reduction. Nevertheless, this kind of scalability is not totally exploited by the rate control (RC) algorithms since the hypothetical reference decoder (HRD) requirement is only satisfied for the highest frame rate sub-stream of every dependency (spatial or coarse grain scalability) layer. In this paper we propose a novel RC approach that aims to deliver several HRD-compliant temporal resolutions within a particular dependency layer. Instead of using the common SVC encoder configuration consisting of a dependency layer per each temporal resolution, a compact configuration that does not require additional dependency layers for providing different HRD-compliant temporal resolutions is proposed. Specifically, the proposed framework for rate-controlled SVC uses a set of virtual buffers within a dependency layer so that their levels can be simultaneously controlled for overflow and underflow prevention while minimizing the reconstructed video distortion of the corresponding sub-streams. This in-layer multi-buffer approach has been built on top of a baseline H.264/SVC RC algorithm for variable bit rate applications. The experimental results show that our proposal achieves a good performance in terms of mean quality, quality consistency, and buffer control using a reduced number of layers.This work has been partially supported by the National Grant TEC2011-26807 of the Spanish Ministry of Science and Innovation.Publicad

Rate Control Initialization Algorithm for Scalable Video Coding

Proceeding of: 18th IEEE International Conference on Image Processing (ICIP), 2011.In this paper we propose a novel rate control initialization algorithm for real-time H.264/scalable video coding. In particular, a two-step approach is proposed. First, the initial quantization parameter (QP) for each layer is determined by means of a parametric rate-quantization (R-Q) modeling that depends on the layer identifier (base or enhancement) and on the type of scalability (spatial or quality). Second, an intra-frame QP refinement method that allows for adapting the initial QP value when needed is carried out over the three first coded frames in order to take into consideration both the buffer control and the spatio-temporal complexity of the scene. The experimental results show that the proposed R-Q modeling for initial QP estimation, in combination with the intra-frame QP refinement method, provide a good performance in terms of visual quality and buffer control, achieving remarkably similar results to those achieved by using ideal initial QP values.The Spanish National grant TSI-020110-2009-103 (AFICUS) and the Regional grant CCG10-UC3M/TIC-5570 (AMASSACA).Publicad

RBF-Based QP Estimation Model for VBR Control in H.264/SVC

In this paper we propose a novel variable bit rate (VBR) controller for real-time H.264/scalable video coding (SVC) applications. The proposed VBR controller relies on the fact that consecutive pictures within the same scene often exhibit similar degrees of complexity, and consequently should be encoded using similar quantization parameter (QP) values for the sake of quality consistency. In oder to prevent unnecessary QP fluctuations, the proposed VBR controller allows for just an incremental variation of QP with respect to that of the previous picture, focusing on the design of an effective method for estimating this QP variation. The implementation in H.264/SVC requires to locate a rate controller at each dependency layer (spatial or coarse grain scalability). In particular, the QP increment estimation at each layer is computed by means of a radial basis function (RBF) network that is specially designed for this purpose. Furthermore, the RBF network design process was conceived to provide an effective solution for a wide range of practical real-time VBR applications for scalable video content delivery. In order to assess the proposed VBR controller, two real-time application scenarios were simulated: mobile live streaming and IPTV broadcast. It was compared to constant QP encoding and a recently proposed constant bit rate (CBR) controller for H.264/SVC. The experimental results show that the proposed method achieves remarkably consistent quality, outperforming the reference CBR controller in the two scenarios for all the spatio-temporal resolutions considered.Proyecto CCG10-UC3M/TIC-5570 de la Comunidad Autónoma de Madrid y Universidad Carlos III de MadridPublicad

A Rate Control Algorthm for Low-Delay H.264 Video Coding with Stored-B Pictures

A rate control (RC) algorithm for H.264 video coding with stored-B (SB) pictures is proposed for low-delay applications. Different models for P and SB pictures are defined for a better QP and MAD estimation. Furthermore, a novel saw-tooth shaped model of target buffer level has also been introduced for a proper bit allocation in GOP structures with SB pictures. Our experimental results show that this proposal outperforms the reference software RC in terms of buffer occupancy and target bit rate adjustment at the expense of slight quality reduction.Publicad

Adaptive Multi-Pattern Fast Block-Matching Algorithm Based on Motion Classification Techniques

Motion estimation is the most time-consuming subsystem in a video codec. Thus, more efficient methods of motion estimation should be investigated. Real video sequences usually exhibit a wide-range of motion content as well as different degrees of detail, which become particularly difficult to manage by typical block-matching algorithms. Recent developments in the area of motion estimation have focused on the adaptation to video contents. Adaptive thresholds and multi-pattern search algorithms have shown to achieve good performance when they success to adjust to motion characteristics. This paper proposes an adaptive algorithm, called MCS, that makes use of an especially tailored classifier that detects some motion cues and chooses the search pattern that best fits to them. Specifically, a hierarchical structure of binary linear classifiers is proposed. Our experimental results show that MCS notably reduces the computational cost with respect to an state-of-the-art method while maintaining the qualityPublicad

Colección de prácticas de acústica de recintos

Grado en Ingeniería de Sistemas Audiovisuales. Asignatura: Acústica de recintosEl objetivo de la asignatura optativa Acústica de Recintos es complementar el contenido de la asignatura troncal Sistemas Electroacústicos y Sonorización, en dos aspectos básicos: El desarrollo de las teorías clásicas de propagación acústica que describen el comportamiento del campo sonoro en el interior de un recinto (estadística, geométrica y ondulatoria) y la profundización en los conceptos de acondicionamiento acústico y aislamiento acústico. Como parte del material de la asignatura Acústica de Recintos, este manual docente incluye los enunciados de tres prácticas a impartir durante la asignatura. Las dos primeras prácticas tienen el objetivo de que el alumno se familiarice con los softwares de simulación acústica en recintos cerrados. De esta forma, es posible reproducir el campo sonoro de recintos existentes o incluso obtener información sobre cómo sonarían recintos que no existen en la actualidad. El manejo de este tipo de paquetes software es muy importante para el alumno, puesto que este tipo de herramientas son básicas para desarrollar entornos de realidad acústica virtual donde se puedan realizar auralizaciones que permitan obtener una representación sonora del espacio simulado. De igual forma, este tipo de herramientas softwares son ampliamente utilizadas en la sonorización de eventos de gran envergadura. La tercera práctica incluye la medida del aislamiento a ruido aéreo entre locales como una forma de cuestionar la mayoría de requisitos que impone la normativa sobre este tipo de medidas, especialmente en lo referente a la medida de tiempo de reverberación y el muestreo del campo sonoro

Cauchy-Density-Based Basic Unit Layer Rate Controller for H.264/AVC

The rate control problem has been extensively studied in parallel to the development of the different video coding standards. The bit allocation via Cauchy-density-based rate-distortion (R-D) modeling of the discrete cosine transform (DCT) coefficients has proved to be one of the most accurate solution at picture level. Nevertheless, in some specific applications operating in real-time low-delay environments, a basic unit (BU) layer is recommended in order to provide a good trade-off between picture quality and delay control. In this paper, a novel BU bit allocation for H.264/AVC is proposed based on a simplified Cauchy probability density function (PDF) source modeling. The experimental results are twofold: 1) the proposed rate control algorithm (RCA) achieves an average PSNR improvement of 0.28 dB respect to a well known BU layer RCA, while maintaining a similar buffer occupancy evolution; and 2) It achieves to notably reduce the buffer occupancy fluctuations respect to a well known picture layer RCA, while maintaining similar quality levels.Publicad

Perceptually-aware bilateral filtering for quality improvement in low bit rate video coding

Proceedings of: Picture Coding Symposium (PCS 2012). Krakow, Poland, May 7-9, 2012Perceptual coding has become of great interest in modern video coding due to the need for higher compression rates. Many previous works have been carried out to incorporate perceptual information to hybrid video encoders, either modifying the quantization parameter according to a certain perceptual resource allocation map or preprocessing video sequences for removing information that is not perceptually relevant. The first strategy is limited by the presence of blocking artifacts and the second one lacks of adaptation to video content. In this paper, a novel and simple approach is proposed, which performs a smart filtering prior to the encoding process preserving both the structural and motion information. The experiments prove that the use of proposed method implemented on an H.264 encoder significantly improves its perceptual quality for low bit rates.Publicad