sourced video is of high quality. If the source’s
quality isn’t measured, then it is junk in and
junk out, no matter how the video is encoded
and sent over the streaming video network.
Solutions
Various operators, suppliers and standards
bodies are working on different aspects of
how to address these issues. The ATIS Internet
Interoperability Forum is working on a standard to correlate end-user quality and source
quality in a streaming video network. Complementary to that, the SCTE is working on
video artifact definitions and measurement
guidelines. The following two resolutions below are based on these developing standards,
and can also be accomplished using various
vendor implementations.
Resolution 1: Junk in, junk out — In any video network, it is critical to measure video quality at origination. For a cable TV, satellite TV
“junk in, junk out” issue arises anywhere
video content is handed
off to another party or
is being re-encoded.
For instance, you
could be monitoring
video at a headend that
has been encoded and
re-encoded several times
by other parts of the
video distribution. Net-
work and MPEG layers
are typically error-free;
however, the impair-
ments are in the content
itself due to prior encoding. Only perceptual
quality monitoring (PQM) can identify visual
artifacts within the content itself and deter-
mine video quality. PQM can identify video
artifacts like: blockiness, blurriness, jerki-
ness, black screen, frozen screen, colorfulness,
scene complexity, motion complexity, ringing
and several other visual artifacts, regardless
of cause. Definitions of these artifacts can be
found in the SCTE HMS177 draft standard.
Most tools that detect these artifacts can also
use them to compute a mean opinion score
(MOS). A MOS is a 1 (bad) – 5 (perfect) score
of the overall video quality representing how
an average viewer would rate the video’s qual-
ity. Using the artifacts and MOS score, you
will know at each point in the video transmis-
sion path if junk in results in junk out.
A
B
Source content ingest
(files or broadcast)
Encode and
segmentation
Origin
servers
CDN
Broadband
C
Resolution 2: End-user quality of experience correlation and potential impacts —
From the first resolution, we know the baseline quality of video prior to encoding and
packaging for a streaming video service. We
also know the quality of each bit rate by segment, so we know how much degradation is
imposed when the content is encoded to a
Figure 1: One of the most
critical places to apply
PQM monitoring is prior to
encoding and packaging
of content (point A).
