KEYWORDS: Video, Computer programming, Molybdenum, Scalable video coding, Video coding, Video processing, Quantization, Visualization, Light sources and illumination, Databases
In video coding, it is commonly accepted that the encoding parameters such as the quantization step-size have
an influence on the perceived quality. It is also sometimes accepted that using given encoding parameters, the perceived quality does not change significantly according to the encoded source content. In this paper, we present the outcomes of two video subjective quality assessment experiments in the context of Scalable Video
Coding. We encoded a large set of video sequences under a group of constant quality scenarios based on two spatially scalable layers. One first experiment explores of the relation between a wide range of quantization parameters for each layer and the perceived quality, while the second experiment uses a subset of the encoding
scenarios on a large number of video sequences. 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 propose a detailed analysis of the experimental results of the two
experiments, bringing a clear insight of the relation between the encoding parameters combination of the scalable
layers and the perceived quality, as well as spreading light on the differences in terms of quality depending on the
encoded source content. As an endeavour to analyse these differences, we propose a classification of the sources
with regards to their relative behaviour when compared to the average of other source contents. We use this
classification to identify potential factors to explain the differences between source contents.
Scalable Video Coding (SVC) provides a way to encapsulate several video layers with increasing quality and resolution in a
single bitstream. Thus it is particularly adapted to address heterogeneous networks and a wide variety of decoding devices.
In this paper, we evaluate the interest of SVC in a different context, which is error concealment after transmission on
networks subject to packet loss. The encoded scalable video streams contain two layers with different spatial and temporal
resolutions designed for mobile video communications with medium size and average to low bitrates. The main idea is
to use the base layer to conceal errors in the higher layers if they are corrupted or lost. The base layer is first upscaled
either spatially or temporally to reach the same resolution as the layer to conceal. Two error-concealment techniques
using the base layer are then proposed for the MPEG-4 SVC standard, involving frame-level concealment and pixel-level
concealment. These techniques are compared to the upscaled base layer as well as to a classical single-layer MPEG-
4 AVC/H.264 error-concealment technique. The comparison is carried out through a subjective experiment, in order to
evaluate the Quality-of-Experience of the proposed techniques. We study several scenarios involving various bitrates
and resolutions for the base layer of the SVC streams. The results show that SVC-based error concealment can provide
significantly higher visual quality than single-layer-based techniques. Moreover, we demonstrate that the resolution and
bitrate of the base layer have a strong impact on the perceived quality of the concealment.
KEYWORDS: Scalable video coding, Video, Computer programming, Video coding, Quantization, Networks, Modeling, Control systems, Signal to noise ratio, Chlorine
Rate 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 confirrmed 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 ρ-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.
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