IEEE Consumer Electronics Magazine - September/October 2022 - 30

Video Technology
Regarding the prediction modes, AV1 supports
two nondirectional modes (DC and PAETH)
and eight directional modes corresponding to
angles between p
4 and 23 p
60 radians. In short, AV1 has 56 intraprediction
20 radians. To those original
eight directional modes, another 48 additional
modes are added, and these vary from each other
by p
modes.
Finally, it should be mentioned that it also has
three nondirectional smooth predictors that perform
block prediction using quadratic interpolation
in vertical, horizontal, or average directions,
with these predictors being called SMOOTH_V,
SMOOTH_H, and SMOOTH, respectively.13 These
can be applied to blocks of all sizes. SMOOTH_V
uses linear interpolation to predict blocks from
the last pixel in the left column and the first pixel in
the top row, while SMOOTH_H performs an analogous
process using the first pixel on the left edge
and the last pixel on the top edge. SMOOTH consists
of an arithmetic average of samples from the
blocks predictedby SMOOTH_V and SMOOTH_H.
In addition, each residual block obtained in
the prediction stage is transformed using a size
that varies from 44to6464 pixels.
EMBEDDED SYSTEMS USED IN THE
ANALYSIS
As indicated above, two embedded systems
have been used to carry out this study and analysis,
and the video encoders described in section
''Standards and Video Encoders " will be
tested on these devices. This section explains
the hardware and software characteristics of
both systems.
Raspberry Pi 4 Board
Specifically, the version used is Raspberry
Pi 4 Model B, with 4 GB of Random Access Memory
(RAM), which was released in June 2019 by
the Raspberry Pi Foundation. Raspberry is an
embedded device consisting of a motherboard
with computer functions that is endowed with a
high level of external connectivity for educational
use, and it can be purchased at an affordable
price.
In terms of hardware features, it is noteworthy
that it has 4 GB of RAM, as indicated by
the version's name. The CPU is a Broadcom
30
BCM2711B0 (64-bit quad-core Cortex-A72) that
works with a clock frequency of 1.5 GHz and
offers two to three times better processing performance
than its predecessor, the Raspberry Pi
3, with a computing power of up to 9.7 gigaflops.
Another novelty with respect to its predecessor
is that it includes 2 USB 3.0 ports, and is able
to perform real-time hardware decoding of 4K
and HD video formats at 60 frames/s (fps) with
HEVC and H.264/AVC, respectively. Furthermore,
it is possible to hardware encode HD sequences
at 30 fps with H.264/AVC. However, it is not capable
of hardware encoding 4K video. Power is supplied
through a USB-C port requiring 5 V and 3 A,
reaching a total power of 15 W.
With regards to the storage space, it is necessary
to incorporate an external SD card to store
the sequences to be encoded/decoded and the
operating system. In this case, there is a SanDisk
Extreme Pro, which is a 64 GB microSDXC storage
card with a read rate of up to 170 MB/s and a
write rate of up to 90 MB/s in order to avoid bottle
necks in the coding process.
Concerning Raspberry 4 software, Raspberry
has Raspbian as its operating system, which consists
of an open-source distribution and free
Linux software based on Debian.
Jetson Nano Board
The multinational Nvidia announced Jetson
Nano in March 2019 at the Graphics Processing
Unit (GPU) Technology Conference. Their bid to
compete in the embedded systems market offers
a small module and excellent computing power
at an economical price. The device is intended
to perform artificial intelligence tasks, for example,
image recognition, instant translation, and
video encoding/decoding.
The Jetson Nano has hardware characteristics
that are typical of medium-performance
computers. Jetson Nano has a quad-core ARM
Cortex-A57 MPCore as its main processor, delivering
up to 472 gigaflops of power. It incorporates
a GPU of the Nvidia Maxwell architecture
with 128 Nvidia Compute Unified Device Architecture
(CUDA) cores. According to Nvidia, Jetson
Nano is capable of encoding 4K videos at
30 fps in HEVC. In addition, it has 4 GB RAM and
4 USB 3.0 ports. It also consumes only between 5
and 10 W.
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