MACHADO NETO, L. T.; http://lattes.cnpq.br/4633981047362163; MACHADO NETO, Luiz Teixeira.
Resumo:
The use of streaming services has grown significantly in recent years, through systems
such as Youtube, Hulu, Netflix, Vimeo, etc. Using the stream, videos are transmitted
and displayed in real time and from anywhere in the world via the Internet. Many
users of these systems use the same in their homes where it is quite common to find
a wireless network (due to the mobility we can achieve through this type of computer
network). In spite of having more mobility, a wireless network is more susceptible to
interference than the wired network so a video can have its picture degraded more
easily just because it is transmitted over a wireless network. We evaluate the transmission
of videos via stream to find out whether the video is actually degraded by
transmission; if different types of content affect the quality of the received video; and
if there are compression standarts (H.264 and MPEG-4 HEVC, the most currently
used) which ensure a better received video quality. Through an experimental approach
with a design of full factorial experiments, several transmissions of videos were made
in the three chosen standarts. In addition to defining the standarts, other variables
were defined as: transmission channel occupancy percentage (in order to evaluate the
degradation of videos according to occupation); power transmission signal (in order to
assess the impact of network signal quality in the video received); amount of motion
in the video (to evaluate whether the amount of motion the video displays impacts
on its quality). For the experiments we used a residential environment that has all
the interference from other networks, just as it can happen in a real environment. To
set the occupancy percentages, experiments were performed to measure the maximum
transmission capacity of the test network. Concerning the quantity of movement, it
was necessary to make a preliminary classification of videos according to spatial and
temporal characteristics of each one. The videos were separated into three categories
and within these categories, three videos were chosen at random to participate in the
experiments. The results show that the HEVC achieved the highest average for quality
metricsofthechosenvideos,andthecodecistheonethatloseslessqualityinawireless
transmission. The amount of movement affects the quality of the received video, and
the greater the amount of motion, the bigger the loss of image quality.