Our mission is to identify and explain the
technologies and applications that allow television services to
be provided through Internet Protocol (IP) data networks.
Readers learn the options and the system to implement IPTV along
with new features and applications and business opportunities
that are available in the IPTV industry today.
IPTV testing involves multiple types of tests
since IPTV systems transmit mixed media, the service can be content
dependent, there are multiple media conversion (encoding) processes,.
There is also an inability to measure the quality of protected (encrypted)
content, and hidden distortion due to error concealment techniques.
Mixed media is the combining of media of
different types. An example of mixed media is the combining of video,
audio, and text graphics on a video or television monitor. The challenge
that this can cause is in the way each media type is processed as it is
distributed through the network. Video and audio processing functions can
result in different amounts of delay or quality resulting in acceptable
quality on one type of media while another type of media has an
unacceptable quality level.
Content dependency factors are a set of
conditions such as rapid motion graphics, that can influence the display
or perception of media. Content dependency causes some types of content to
look good while other types of content look bad given the same network
performance impairments. This means that the user's perceived quality can
vary on the same network depending on the content that is sent through the
Multiple Media Conversions
Multiple media conversions are the process of
changing information from one format to another format. There may be
several conversion processes along the content flow path in IPTV systems
and one or more of them may degrade the quality of the media.
IPTV media conversion commonly uses lossy media
compression. Lossy compression is a process of reducing an amount of
information (usually in digital form) by converting it into another format
This article is
Part 2 of a 11 Part Series
Intro to IPTV Testing List
IPTV Testing Requirements
IPTV Testing Challenges
IPTV Testing Types
IPTV Quality Metrics
Video Quality Metrics
IPTV Network Measurements
Content Quality Metrics
Command and Control Metrics
Content Quality Rating Systems
IPTV Test Equipment
(such as MPEG) that represents the initial
form of information. Each time the media is converted, additional
The content producer (such as a studio)
provides the media to a content distribution system (such as a
satellite distribution system), usually in high-quality uncompressed
form. Content distributors may compress the media and send it to
broadcasters (such as IPTV systems). When it is received by the IPTV
systems, it is decoded and re-encoded for local distribution. The
re-encoding process may be in another compressed format (such as
MPEG-4). The encoder may change the media format from variable bit
rate (VBR) to constant bit rate (CBR). Each of these conversions can
add distortion to the media signal.
Figure 1.3 shows how content may be
converted multiple times between its high-quality format and when the
media is received by the viewing device. This example shows that the
media is compressed and encoded into MPEG-2 before it is distributed
via a satellite system. When the satellite signal is received at the
cable head end, it is decoded, switched with other video sources, and
re-encoded into MPEG-4 before it is distributed to the viewer.
Content Protection is the end-to-end
encryption system that prevents content from being pirated or tampered
with in a communication network (such as in a television system).
Content protection involves uniquely identifying the content,
assigning the usage rights and scram-
Figure 1.3, IPTV Multiple Conversions
bling and encrypting the digital assets prior to play-out or storage (both in the network or end user devices), as well as delivering the accompanying rights to allow legal users to access the content. When content is encrypted or uniquely encoded, it is usually not possible to analyze the underlying media.
Error concealment is a process that is used by a coding device (such as a speech coder) to create information that replaces data that has been received in error.
Error concealment is possible when portions of the
signal output of the coder have some relationship to other portions of the signal output and that relationship can be used to produce an approximated signal that replaces the lost information period (lost
bits). Error concealment methods (such as repeating the last frame of video when a frame is lost) can influence the ability to accurately measure the effects of distortion (such as packet loss).