One-pass Bitrate Control for MPEG-4 Scalable Video Coding using rho-domain

International audienceThis paper presents an attractive rate control scheme for the new MPEG-4 Scalable Video Coding standard. Our scheme enables us to control the bitrate at the output of the encoder on each video layer with great accuracy. Each frame is encoded only once, so that the computational complexity of the whole scheme is very low. The three spatial, temporal and quality scalabilities are handled correctly, as well as inter layer prediction and hierarchical B frames. A linear bitrate model is used to predict the output bitrate for a frame, based on a simple and effective framework called rho-domain. A coding-complexity measure is also introduced to dispatch the available bits among the frames, in order to reach a constant quality throughout the encoded video stream. To attest the performances of our rate control scheme, we present comprehensive results on some representative scalable video set-ups

Rho-domain based Rate Control Scheme for Spatial, Temporal and Quality Scalable Video Coding

International audienceRate control is a capital issue in video coding. It allows a regulation of the bitrate out from the encoder, to cope with some network transmission or quality constraints. Scalable Video Coding emerged several years ago as an answer to the growing need of application-adaptable video streams. Although the interest of scalable video coding has been confirmed by recent studies, it can not be used in practical contexts without proper rate control techniques. In this paper we present a new rate control scheme for scalable video, based on a simple yet attractive bitrate modelling framework called -domain. Our scheme performs accurate rate control on spatial, temporal and quality scalabilities, while maintaining a constant PSNR. Inter layer prediction is also handled effectively

Subjective Quality Evaluation of H.264 High-Definition Video Coding versus Spatial Up-Scaling and Interlacing

International audienceThe upcoming High-De nition format for video display provides high-quality content, especially when displayed on adapted devices. When combined with video coding techniques such as MPEG-4 AVC/H.264, the transmission of High-De nition video content on broadcast networks becomes possible. Nonetheless, transmitting and decoding such video content is a real challenge. Therefore, intermediate formats based on lower frame resolutions or interlaced coding are still provided to address targets with limited resources. Using these formats, the nal video quality depends on the postprocessing tools employed at the receiver to upsample and de-interlace these streams. In this paper, we compare the full-HD format to three possible scenarios to generate a full-HD stream from intermediate formats. We present the results of subjective tests that compare the visual quality of each scenario when using the same bitrate. The results show that using the same bitrate, the videos generated from lower-resolution formats reach similar quality compared to the full-HD videos

Influence of the source content and encoding configuration on the perceived quality for scalable video coding

International audienceIn video coding, it is commonly accepted that the encoding paramaters such as the quantization step-size have an influence on the perceived quality. When dealing with Scalable Video Coding (SVC), the parameters used to encode each layer logically have an influence on the overall perceived quality. It is also commonly accepted that using given encoding parameters, the perceived quality does not change significantly according to the encoded source content. In this paper, we evaluate the impact of both SVC coding artifacts and source contents on the quality perceived by human observers. We exploit the outcomes of two subjective experiments designed and conducted under standard conditions in order to provide reliable results. The two experiments are aligned on a common scale using a set of shared processed video sequences, resulting in a database containing the subjective scores for 60 different sources combined with 20 SVC scenarios. We analyse the performance of several source descriptors in modeling the relative behaviour of a given source content when compared to the average of other source contents

Stratégies d'encodage pour codeur vidéo scalable

This work is about designing bit rate control technics for the MPEG-4 Scalable Video Coding standard. The proposed approach benefits from a low computational complexity, so that its impact on the encoding time is very small. The quality of the encoded stream is also considered when controlling the bitrate in order to obtain optimal visual impression. With today's heterogeneous communication technologies and video-reading devices, broadcasting video content requires large amounts of time and money to provide the user with optimal quality in any context. Scalable video coding has been developed as an answer to this need for adaptive video streams. In 2008, the MPEG-4 Scalable Video Coding (SVC) extension was finalized. To address the adaptivity issues, this new standard provides three types of scalabilities. Spatial, temporal and quality scalabilities allow a video stream to adapt the dimensions, the number of frames per second and the fidelity depending on the target's requirements. Bit rate control is an important part of the encoding process as it allows to adapt the bitrate at the output of the encoder to the target's constraints. Unlike most of the existing approaches, our rate control technic is designed to have a low computational complexity. First, a bit rate per second constraint is specified for each video layer. Then, the available bits are dispatched among frames so that constant quality can be achieved in the decoded stream. The respect of the specified budget is finally enforced by a bit rate model, based on a simple and effective framework called $\rho$-domain. Using the statistics of the frame, this model allows us to choose the optimal quantization parameter while maintaining the amount of calculations very low. Based on this simple technic, we propose two approaches. In the first approach, each image is pre-encoded to provide the bit rate model with the statistics of the frame before rate control. This approach allows us to regulate the bit rate with great accuracy, as the bit rate error is below 3\% of the specified constraint on each type of scalability. In the second approach, rate control is performed using the information from the previous frame, so that no pre-encoding step is required and each frame is encoded only once. Thus, the impact on the encoding process is greatly reduced, at the cost of a small error increase. Finally, perceptual quality is considered when dispatching the bits among frames, so that quality variations are reduced and visual experience is improved. Our bit rate control technic for MPEG-4 SVC shows great accuracy on all spatial, temporal and quality scalabilities. Its low complexity, together with quality variation control make it a valuable contribution, especially in practical applications, for which time ressources are limited and the user-felt quality is important.Les travaux de cette thèse ont pour but de développer des stratégies de régulation de débit pour le codage vidéo scalable MPEG-4 SVC. Plusieurs approches sont proposées, en fonction des besoins en termes de précision et de la complexité désirée. La qualité du flux vidéo décodé est également prise en compte afin d'améliorer l'impression visuelle. La multiplication des moyens de transmission et la diversification des appareils capables de lire du contenu vidéo contraignent les diffuseurs à dépenser beaucoup de temps et de moyens pour être en mesure de fournir une qualité de vidéo optimale quel que soit le contexte. La vidéo scalable a été développée en réponse à ce besoin d'adaptation des contenus vidéo aux différents contextes de diffusion. Le standard H.264/MPEG-4 SVC (Scalable Video Coding) propose trois types de scalabilité (spatiale, temporelle et en qualité), qui permettent d'adapter la résolution, le nombre d'images par seconde et la qualité du flux en fonction des besoins. Un flux vidéo unique est encodé, contentant plusieurs couches de résolution différentes codées les unes par rapport aux autres, de façon à rendre le codage de l'ensemble plus efficace. La régulation de débit permet d'adapter le débit en sortie de l'encodeur pour respecter des contraintes liées à la transmission ou au décodage du flux vidéo. À partir d'une consigne donnée, le budget à respecter est réparti entre les différents éléments du flux. Un modèle de débit est ensuite utilisé pour anticiper le comportement du débit en fonction des paramètres d'encodage afin de respecter les contraintes imposées au flux. À partir de cette problématique, deux approches sont proposées. La première se base sur un pré-encodage de chaque image pour fournir une base de calcul au modèle de débit. Elle permet d'obtenir une régulation très précise, avec une erreur entre le budget alloué et le débit effectif inférieure à 7\% sur les trois types de scalabilité. La seconde approche utilise les informations rassemblées dans les images précédentes comme base pour le modèle de débit de l'image à encoder. Elle ne requiert pas de pré-encodage, et ne pénalise pas la complexité du processus d'encodage. En outre, la perte de performances par rapport à l'approche en deux passes est minime et la consigne de débit par seconde est respectée de manière précise. Enfin, une méthode permettant de réduire les variations de la qualité est proposée pour améliorer l'impression visuelle ressentie par l'utilisateur. Les résultats montrent que la méthode présentée est capable de réguler le débit avec une grande précision sur les trois types de scalabilité, tout en réduisant les variations de la qualité et en conservant une complexité de calculs très faible. Ces atouts la rendent non seulement intéressante du point de vue des performances, mais également applicable dans des contextes pratiques où les ressources en temps sont limitées

Rho-domain based Rate Control Scheme for Spatial, Temporal and Quality Scalable Video Coding

International audienceRate control is a capital issue in video coding. It allows a regulation of the bitrate out from the encoder, to cope with some network transmission or quality constraints. Scalable Video Coding emerged several years ago as an answer to the growing need of application-adaptable video streams. Although the interest of scalable video coding has been confirmed by recent studies, it can not be used in practical contexts without proper rate control techniques. In this paper we present a new rate control scheme for scalable video, based on a simple yet attractive bitrate modelling framework called -domain. Our scheme performs accurate rate control on spatial, temporal and quality scalabilities, while maintaining a constant PSNR. Inter layer prediction is also handled effectively

Rho-Domain for low-complexity rate control on MPEG-4 Scalable Video Coding

International audienceScalable Video Coding was designed in response to the growing need for flexibility in video transmission over networks and channels. MPEG-4 Scalable Video Coding (SVC) is a recently finalized standard which introduces new coding tools such as spatial, temporal and quality scalability, to produce a layer-based scalable video stream. Additionally, inter-layer prediction allows a layer to use information from other layers as a basis for motion and texture prediction, improving the overall coding efficiency. Rate control is a capital issue in video coding, as it is designed to regulate the bitrate at the output of the encoder and keep it close to a specified constraint. Whereas rate control has been extensively studied for non-scalable video coding, only few propositions were made for scalable video coding. In this paper, we adapt an attractive rate control approach, based on a bitrate modeling framework called rho-domain, for scalable video coding. We show that this model performs well on all spatial, temporal and quality scalabilities, and handles inter-layer prediction quite accurately. After validating the approach in MPEG-4 SVC, we use the rho-domain model to build a simple-accurate rate control scheme. Results show that the mean frame bitrate error is below 7% on a representative set of configurations, while the impact on the complexity of the encoder is very low