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CD and DVD
playback compatibility
Quality parameters for CD and DVD production
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As
digital distributions media CD and DVD have the distinct advantage that
the content is an exact copy of the original. A copy will be identical in
content - and quality - to the master file from which it is made.
The tape-based distribution of the past relied on a domestic quality copy
- usually on VHS - of a professional video master tape. The duplication
process implied an unavoidable degradation in comparison to the master,
simply because the distribution format - VHS - had a lower bandwidth than
the original master. Despite this, tape-based distribution was usually
quite reliable - even the roughest copy could usually play on a good
quality player, just as one could hope that even a poorly maintained
player could play a good copy. The defects in both cases would be there to
see and hear, but it usually worked.
With digital distribution based on CD or DVD, the technical quality is
very high. However it can be difficult to ensure 100% playback
compatibility - the ability of a given disc to playback without faults on
any CD or DVD player. Where the analogue technology of the past would have
probably given at least a recognizable picture and sound, today's digital technology
usually works either perfectly - or not at all.
There can be many causes of the problems
that the end user may experience when trying to play a CD or DVD. Many of
these are within the control of the producer of the DVD, and given the
correct authoring and encoding tools they may be eliminated. Other causes
of playback problems may exist far outside the control of the producer -
simply because the technology of DVD, especially when being played on a
computer, relies on hardware and software which is specific to the end
users computer. Whilst the problem is most noticeable on computers,
dedicated set-top DVD players are also vulnerable to end user
configuration errors, which in some cases can give the impression that a
DVD may be at fault.
Channel 6 Television produces CD and DVD productions according to a
"cook-book" which ensures the optimal playback compatibility by
addressing the following issues -
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Authoring and encoding
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The
files which constitute the content of a CD or DVD are produced using
tested and popular state-of-the-art professional authoring and encoding
tools. These tools employ "recipes" and algorithms which comply
fully with the industry standards to ensure that the resulting data may be
played without problems. During encoding we take particular care to ensure
that the programme bit-rate does not exceed the ability of DVD drives,
players and platforms to read and process the data without loss of
continuous and synchronous playback. The same attention is given to the
creation of media files for web-streaming and download, or for playback
via an intranet server.
At the same time, we ensure that the files and their composition on the
delivery medium are fully compliant with the playback technology. Once can
find many media releases, especially on DVD, where the producer has
included additional bonus files, which are not necessary for playback of
the primary payload - a film or television programme. Whilst a DVD often
has the capacity for additional material, some DVD players will be
confused by this extra data, sometime to the extent that they will not
play the main feature. Therefore we avoid this strategy at all costs.
There is some difference between how a DVD drive in a computer handles
data, and how freestanding DVD player does the same job. As most DVD
releases are targeted towards both playback platforms, it is necessary to
work to the lowest common denominator when choosing how to author a DVD to ensure the optimal playback compatibility. |
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Raw media
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Both DVD and CD raw media (blank discs) are
available in differing levels of quality. When planning the release of a
large number of DVD discs, it can be tempting to choose a cheaper
raw-media - but the benefits of such a choice may be short-lived indeed.
It is well known that cheap - so-called "no-name" - disc media
are one of the most typical causes of playback incompatibility.
A reliable CD or DVD "burn" implies that the foil, that is
sandwiched in the disc, is perforated during the burning process with
exactly the correct intensity, otherwise the end user's player may not be
able to read the data properly. If the characteristics of the
"no-name" foil are outside the usual strict tolerance, the data
integrity may be sufficiently weak for an older DVD player - which itself
could be functioning slightly under specification - to achieve proper
playback.
For this reason, Channel 6 Television uses only high-quality media for CD
and DVD - we have used use the best Verbatim media for several years - and
we have never experienced a faulty disc.
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Burn speed
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Many newer CD and DVD writer drives allow burn
speeds up to x48 - the burn speed is the single parameter which has most
influence on how quickly a DVD producer can duplicate a given DVD order,
and is therefore a factor which influences the price for the job.
There is however a clear correlation between the speed used to burn a DVD
and the resulting products playback compatibility. Faster burn speeds can
result in data which is harder for some (not all) DVD drives to read
accurately. In general, some older DVD drives in both computers and
set-top players are more prevalent to difficulties when reading high-speed
burnt DVD's.
Like many aspects of playback compatibility, this is a complex issue
because it is usually only some discs which cause problems in some drives
- and vice versa.
There is only one simple solution to this problem - burn DVD copies
slowly. Therefore Channel 6 Television has a rigid product policy which
dictates that speeds exceeding x8 are not employed for any distribution
release disc. Furthermore, all duplicated discs are immediately verified
for data integrity before packing and delivery to the customer.
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DVD writer drives
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Despite falling hardware prices in recent
years, there is still some difference in quality and reliability between
CD and DVD writer drives from different manufacturers - the quality of the
drive 8and therefore the burn) is a vital factor when striving for high
playback compatibility.
Channel 6 Television uses Pioneer duplication drives because Pioneer have
offered a consistency of quality and reliability for many years.
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| Glass
mastering |
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The
most reliable mass-duplication method employs glass-mastering technology.
Instead of "burning" minute holes in sandwiched foil - as a PC
based writer drives does, the foil is perforated using a glass
"stamp" - before it is laminated within the polycarbonate
plastic layers. The process is very fast - but also more expensive to tool
up when compared to burning technology - therefore it is a more applicable
technology for large quantity DVD releases - for example over 1000 copies.
Whilst glass mastering is probably the best technology for eliminating
manufacturing errors which can cause playback incompatibility it is
important to understand that this technology does little to reduce the
incidence of playback incompatibility which is caused by configuration
errors on the end-user's playback equipment. |
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| Playback
compatibility and the end user's equipment |
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The
majority of the potential causes of playback compatibility of
professionally produced CD and DVD releases are to be found in the end
user's equipment. There are several reasons for this -
CD technology is now almost 30 years old, and DVD has been with us in various
formats for over a decade. This legacy has resulted in a variety of
different technologies, many of which are still in use in end users'
computers and DVD players. Despite the fact that the recent advance of DVD
has resulted in many older CD drives (which were particularly prone to
playback errors on burnt CD's) being taken out of commission, there are
still many older DVD drives in use, which have difficulty handling all
media.
The same is the case for some older DVD players - some older models can
have difficulty with certain file formats, and it is far from all DVD
players which can be - and are configured correctly to handle content in
both 4:3 and 16:9 aspect ratios. Similarly, many newer flat-panel TV's
require user configuration to ensure the correct aspect ratio display.
This problem can become exaggerated, when handling a DVD with content on
both formats - resulting often in the end user needing to select the
desired format manually. To make matters worse, many so called widescreen
TV and computer displays and are actually 14:9 rather than 16:9, so
automatic configuration features to "fit the signal to fill the
entire screen" will usually result in an incorrect aspect ratio.
Some DVD drives and their associated player software have difficulty
handling DVD discs with less than approximately 400MB data on a 4.7GB DVD.
These drives interpret such a disc as "missing data". For this
reason, our duplication software adds additional "null data" to
the burnt tracks of low-data DVD's so that these discs are interpreted by
most drives as fully "DVD-legal".
The majority of current DVD drives and players - in combination with
modern displays, are able to handle all aspect ratios and audio formats -
but even here such equipment may rely on correct user configuration.
Both DVD players and computer based DVD drives and software may be
confused by the complex menu structures and copy-prevention measures
employed on some DVD releases. This problem is not even unknown on major
American studio releases.
Whilst there is no such thing as the "perfect DVD", most
problems can be avoided by a professionally authored and duplicated
product where the authored features are selected with regard to the
end-users requirements.
The problem is a great deal more complicated when we look at computer
based DVD players.
Whilst the hardware and software configuration in most free-standing DVD
players is "fixed at the factory" - with only a limited, albeit
vital, number of configuration options available to the end user, the
configuration of a DVD drive and media player software in a computer is
subject to constant change - often without the end user being aware of
such changes.
The relationship between the operating system, DVD player hardware and
software, graphics and audio cards, and the many "codecs" -
software devices which decode audio and video data before it can be
played, is a critical one. Regular software updates - often delegated to
the operating system's automatic functions or the automatic update
features of a variety of installed media players - many of which compete
for resources and priority with each other - can easily result in
conflicts between these components which result in some or all media types
being unable to play properly.
For this reason, when facing playback incompatibility with any given
media, irt is usually worth examining the end user's system configuration
before suspecting the integrity of a CD or DVD.
This is too complicated a subject to deal with on these pages. There are
many "good recipes" for the configuration of a computer - not
only to home and office use, but also for professional workstations such
as those we employ in our production facilities.
Whilst many "configuration-tips" many be particular to specific
hardware or software configurations, it is our experience that there are
many working methods which will benefit any computer - regardless of the
specific configuration, and in some cases, regardless of the individual
operating system. Our configuration "cook-book" does not simply
address the configuration of media devices, but rather a range of methods
and approaches which together will ensure that a computer runs in a stable
manner for all applications.
For those who have a technical interest in the subject, our configuration
cook-book is available (in English) on our technical
documents download page. |
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| A
word about software media players |
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There
was a time that media players such as Windows Media Player or Quicktime -
and many others - were simple players. But particularly since the launch
of Windows XP, such players - which are often available for free - have
become the basis for big-business for those companies that release them.
Media players are no longer simple players - they are becoming
increasingly integrated into the operating system and the user interface,
as their producers compete for the user's loyalty to their player
application. Configuration of many of these players is often quite
complicated, so that many users simply accept the application's default
settings.
This of course is exactly what the application publisher hopes and plans
for - as their player's default settings usually capture functionality or
priority from other, competing applications that may already be installed
- all in the quest for becoming "My preferred media player".
Windows Media Player, Quicktime and Real Player are all examples of this
trend. Often such players and their default configurations result in the
implementation of often useless additional features that simply eat memory
or processing resources. Often such optional "goodies" are
the economic payload, which made distributing the player free of charge
possible.
We know by experience, that it can take an hour or two to install and
configure the 5-8 media players and other media applications we use, in
such a way that they do not conflict with each other, and so that it is us
who decide which player should be used for with type of media. But it is
time well-spent.
For the home or office user without broad experience in the configuration
of multiple media applications, it is always worth considering whether the
free player that one can download on the internet is something that one
really needs, and one is able to configure properly. |
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| Quality
control of media releases |
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Here
at Channel 6 Television, all CD, DVD and streaming or download media
products are thoroughly tested on a wide range of platforms before the
product is released to the customer. The computer based test routines
cover a range of players and different operating systems on both laptop
and desktop platforms.
Similarly, all DVD releases are tested in free-standing DVD players.
Media files for internet streaming and download are tested online via our
own remote web-server before they are released to the customer. In many
cases the approval and delivery process for such files is accomplished
online via our web-server, giving the customer an immediate indication of
how the product will function in the real world. |
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| If
you have any questions or comments about playback compatibility and our
quality control measures you are welcome to contact us. |
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channel
6 television denmark
Foerlevvej 6, Mesing,
8660 Skanderborg
telefon 86 57 22 66
telefax 86 57 22 16 |
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