In Broadcast - March 2014 - 49

WWW.INBROADCAST.COM | ISSUE 29 - MARCH 2014

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Let's Get Objective
About QoE Systems
By Simen K. Frostad
Chairman, Bridge Technologies

veryone knows the joke about
the tourist winding down his car
window and asking a local man
how to get to the coast. The local
scratches his head and says: "Well
I wouldn't start from here."
It's good advice for anyone
thinking about implementing
a Quality Of Experience (QoE)
monitoring system. QoE is deemed
to be an essential facet of a good
monitoring strategy for digital media
operators, but the conventional
approach to QoE for digital media
has some surprising origins.
Monitoring QoE ﬁrst began in
the telecoms industry, when telcos
wanted to assess how phone users
felt about the sound they were
hearing. They assembled panels
of experts who evaluated the
aural quality, often by listening to
a selection of stock phrases such
as 'You will have to be very quiet',
'There was nothing to be seen', and
'They worshipped wooden idols'.
The experts recorded their scores,
assessing impairments on a scale
of one to ﬁve, from 'imperceptible'
to 'very annoying'.
The scores were then averaged
and weighted using statistical
manipulations common in the
social sciences and market research.
This methodology was called
MOS (Mean Opinion Score), and
speciﬁed by the ITU-T (International
Telegraph Union).
It certainly made sense to use this
subjective approach for telephony,
because the quality and intelligibility
of sound over a phone line is difﬁcult
to evaluate using more precise

and objective measures. But as a
methodology for visual media and
digital media transmissions? Well,
you wouldn't start from here...
And yet, that is precisely where
most conventional QoE monitoring
solutions for digital media do start.
MOS may have been reinvented
as VideoMOS, and the evaluation
panel may have been robotised - so
now it's algorithms that attempt to
simulate the subjective reactions
of a range of 'typical' viewers - but
the methodology is still based on
the premise that subjectivity is
the key to QoE.
Subjectivity is subtle: a human
viewer watching a top-quality 1080i
transmission of the Superbowl,
followed on the same channel by
the 1940s B&W movie Casablanca
knows that the two pieces of
content cannot be judged by the
same criteria. Yet in a robotised QoE
assessment based on MOS criteria,
the Superbowl would score highly,
while Casablanca would be marked
way down for 'blurriness', scratches
and other artifacts, and for its lack
of resolution and colour. These are
spurious and misleading results,
making the data from this kind of
QoE system of questionable value
to the provider.
Fortunately there are plenty of
criteria inherent to digital media that
are readily evaluated in a completely
objective way: lost packets, timeouts,
buffering, and so on.
By basing QoE monitoring on
these, it's no longer necessary to
confect an algorithmic 'opinion'
about Quality Of Experience.

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Copyright © 2014. Clear-Com, LLC. All rights reserved. ® Clear-Com, the Clear-Com logo, and Eclipse are registered trademarks of HM Electronics, Inc.
Tempest and Tempest logo are registered trademarks of CoachComm, LLC.

QoE board at IBC 2013

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