Whether you know it or not, many of the videos that you watch have been con- figured using video quality metrics. Oh, you disagree? Well, have you have
watched Netflix recently? Over the last 2 years
or so, Netflix’s encoding ladders have been
driven by the company’s Video Multimethod
Assessment Fusion (VMAF) metric and, before
that, Peak Signal to Noise Ratio (PSNR). Not a
Netflix customer? Well, how about You Tube?
You Tube uses a neural network based upon
constant rate factor encoding, which itself is
driven by an internal video quality metric.
Simply stated, video quality metrics attempt
to predict how a subjective viewer would rate
a particular video, and metrics are comparatively rated based upon the accuracy of these
predictions. Of course, there are many purists
who insist that subjective comparisons are the
only valid technique for gauging quality, and
indeed, properly administered subjective tests
are the gold standard.
However, when you consider that 400 hours
of video are uploaded to You Tube each minute,
you can appreciate that the service has a strong
need to encode its streams as efficiently as pos-
sible and a total inability to deploy humans to
make it happen. Even Netflix, with a compara-
tively paltry 1,000 hours of new content in 2017,
can’t use human eyes to create the customized
encoding ladders for each video. For both com-
panies, and many others, objective quality met-
rics are essential.
The bottom line is that if you’re in charge of
encoding for your organization, and you’re not
using objective video quality metrics in one
form or another, you’re behind the curve. Fortunately, you’re also in the right place. In this
article, I’ll provide an overview of what video
quality metrics are and how they work, introduce you to the most common tools for applying them, and tell you how to choose the best
metric and tool for your needs.
What Metrics Measure (And How)
You’ve probably heard of metrics like PSNR,
Structural Similarity index (SSIM), and perhaps
even Netflix’s VMAF. To understand how they
differ, it’s useful to understand how each came
about and what each measures.
By Jan Ozer
If you’re not using a video quality measurement tool, you’re behind
the curve. Here’s a look at the most popular tools and how they work.
CHOOSING AND USING