tektronix_tektronix 28/11/2013 16:50 Page 1
Adaptive Bitrate
Streaming
Monitoring and
Quality Control
Monitoring and quality control of
Adaptive Bitrate Streaming platforms is
as important as the ABR systems
themselves, according to test,
measurement and monitoring solutions
specialist Tektronix.
ontent Providers,
Broadcasters and
Operators are all
seeking to provide
multiscreen video or TV
Everywhere, as it is also
sometimes called. This is
intended to deliver
streaming video services to
PCs, laptops, smartphones,
tablets and TVs.
Streaming to such a wide
range of devices is complex. Each
type of device has its own unique
demands. The data rate an IPenabled television needs to
present an acceptable picture is
far greater than that necessary for
a smartphone. In addition, the
networks that some of these
devices use can suffer from
dynamically changing
characteristics.
The underlying technology
used with multiscreen video is
adaptive bitrate streaming (ABR).
This essentially is the segmenting
of content into small fragments of
compressed content for
transmission to viewing devices.
This technology is not
standardised in the same way that
DVB Transport Streams are used
in traditional TV applications.
There are several ABR
implementations: Apple’s HTTP
Live Streaming; Microsoft’s
Smooth Streaming; Adobe’s
HTTP Dynamic Streaming and
MPEG-DASH, each having
different characteristics.
A recent survey identified
C
22 EUROMEDIA
‘quality of experience/quality of
service’ as the second most
significant technical challenge
(after bandwidth limitations) in
offering OTT video. “ABR is a
simple idea that is both clever but
hard to implement,” said Paul
Robinson, Tektronix’s CTO for
Video. “There is a lot that can go
wrong. You have to check that
everything is working as you
think it is. The only other way to
find out when things are going
wrong is to wait for subscribers to
tell you, and you don’t want to
find out that way.” Monitoring
and Quality Control (QC) of ABR
platforms is as important as the
ABR systems themselves.
One of the biggest challenges
of content streaming is that the
networks and devices are far
more varied than those found in
the more controlled environments
of Cable, Satellite, Terrestrial and
IPTV. Different network
conditions and device
requirements make a highly
adaptable architecture necessary.
ABR addresses this issue
dividing the stream into discrete
fragments of fixed time duration.
These are referred to as
fragments, segments or chunks. A
variety of bitrates for the
fragments is established
commonly referred to as profiles.
The device displaying the content
has the intelligence to request the
appropriate profile that best suits
network conditions at any
particular point in time. The
optimal profile can change each
time a fragment is requested. Any
ABR system works by checking
the playout devices buffer to see
how full it is. If it is becoming
full, the device requests a lower
bitrate profile. As the buffer
empties the device requests a
higher bitrate profile. In theory
this ensures that constant playout
is maintained without the
‘buffering’ issues experienced
with tra ditional progressive
streaming systems.
Ensuring subscriber
satisfaction with such a complex
architecture requires monitoring
QoE and QoS at multiple points
in the network to ensure that the
content is of appropriate quality
and that the delivery network is
actually capable of delivering the
content.
QoE and QoS
There are two linked ways of
ensuring subscriber satisfaction,
Quality of Experience (QoE) and
Quality of Service (QoS). They
may have similar sounding
names, but they are significantly
different.
QoE is a relatively new area
for operators. In the past,
operators focused on measuring
attributes related to the precision
of the IP packet transport and the
MPEG Transport Stream. For
example, at the IP level, these
QoS measures focused on
delayed, out of order, and lost
packets. Recent technology
advances have allowed operators
to use deep packet inspection to
look for deeper content related
problems. These QoE measures
come far closer to identifying the
actual experience viewers will
have when they see and hear the
video and audio.
The overall monitoring of ABR
streams are performed at four
points using a two-step process.
The first step relates to content
preparation and is performed at
the QoE level. Monitoring is
performed before and after
transcoding, but before
fragmentation and the addition of
digital rights management
(DRM). The second step relates to
content delivery and is a network
level QoS function that ensures
content can be delivered
correctly. Monitoring is
implemented after the origin
servers and CDN
caching/streaming servers.
Content Preparation
The first important point in the
monitoring and Quality Control
(QC) of ABR platforms is that the
ingested content must be error
free when received by the
operator. If there are flaws in the
ingested video and audio, it is
inevitable that the final service
will not be acceptable.
Transport Streams that arrive
at the operator’s ABR head-end
from its own encoders or from
other broadcasters and content
providers are monitored for QoE
issues such as macroblocking,
compression artefacts, audio
silence, levels and loudness.
(Point 1 in the graphic).
The ingested content is then
transcoded into each of the ABR
profiles (the same content at
various bitrates) that the operator
supports. The content quality of
each profile is then verified after
transcode. (Point 2 in the
graphic).