Feature Article - The Digital Link: Understanding the Digital Home
Video Controversy on Commercial Content (Copy) Protection - February,
In this new
millennium, there is a convergence of technologies into a digital format.
Cassette tape players have been replaced with the CD. VHS players have been
replaced with the DVD. The Sony Walkman® has been replaced with the MP3
portable. This rapid development of digital technology has the average consumer
replacing functional equipment with newer technologies. The "in with the new and
out with the old" attitude can be quite costly for the consumer. In this
discussion, I have focused on Home Theater and HDTV; specifically the Media
Industry’s application of Commercial Content Protection (CCP). Their involvement
will force you to buy a new TV in two years.
High Definition Television (HDTV)
In 1981, the first demonstration of HDTV at the Society of Motion Pictures and Television Engineers (SMPTE) annual conference in San Francisco took place. 11 years later, in 1992, the FCC gave the TV industry 6 years to start broadcasting HDTV. Many of us are still waiting.
Figure 1 - Relative resolution
of TV formats. Austin Powers,
The advantages of HDTV are obvious: better
resolution, better signal quality. Your average cable TV comes in at 640x480
(NTSC), while HDTV can receive 1920x1080. If you look at Figure 1 on the right,
which simulates the relative resolution of several formats, you can see clearly how much more picture resolution HDTV offers.
The TV industry was virtually forced to move to HDTV by the FCC. Unfortunately, no one forced the Movie Industry to do the same thing. So here we are in 2002 watching DVDs with a resolution of 720x480 on a HDTV capable of more than twice that.
There are two reasons why the movie industry has taken so long to get HDTV content into our hands: Content (Copy) Protection and Media. Compressed DVD video takes up about 3.5-4.7 Mb/s on the DVD. With a dual layer DVD holding about 7.95 GB, you end up with about 3.8-5 hours of video on a Dual Layer DVD. The new Superbit DVDs use less compression and stay near the max of 7 Mb/s, so they get about two hours on a disc. HDTV needs about 20 Mb/s compressed (broadcast quality) to 24 Mb/s depending on quality , so a two hour video needs over 20 GB of disc space. Besides capacity, the DVD format only supports a 9 Mb/s transfer rate, making even short portions of HD content unavailable on DVD.
Content Protection (Copy Protection) is a big issue
for the movie studios. They don't want you to be able to make a perfect copy of
movies, which is definitely possible with movies in digital
As you can see from Figure 2, HDTV requires a lot of storage space. Current DVDs don’t have enough room for a feature-length movie.
Figure 2 - Bit rate in megabits per second and gigabytes per hour of compressed digital video.
Blue laser DVD: This year at CES Toshiba was showing a prototype of a blue laser DVD player. With capacities of 30 GB, this could be the answer for HD-DVD. As of 2/19/2001 the standard has been accepted by major manufacturers. Expect them in 2003.
D-VHS: JVC has introduced a digital VHS
tape capable of storing 44.4 GB of digital data per cassette. Their new player
is equipped with a DVI output as well as analog output. Most people in the
industry still feel that HD-DVD will be the mass market solution, as opposed to
Besides DVD, HDTV can be delivered through any medium that can support the 20 MB/s of bandwidth. Dish and DirecTV offer HDTV programming from satellite. Local Cable companies will be able to send HDTV feeds through their digital cable networks to your home.
With all the benefits of HDTV, it’s a shame we are converting it to an analog signal (losing quality when we do) to send over cables to the HDTV set. With the advent of digital projectors and digital TVs, the signal must then be converted back to digital format from analog (again losing quality). If we have digital media and digital displays, why then are we converting it to analog along the way?
Digital Connection / Transport
We would all like to have a total-digital-experience from source to TV screen, and from source to speakers. The first obstacle to this is the DVD player licensing agreement from the DVDCCA that each manufacturer must sign before they can have the decryption keys to unlock DVDs. When players first were developed, the license agreement STRICTLY PROHIBITED any digital output of the CSS-encoded video (CSS means Content Scrambling System). At the time the first generation (and second really) players were built, there was no encryption scheme developed for uncompressed high bandwidth consumer video. HDTV wasn’t very popular around that time anyway.
Once HDTV started to catch on, consumers had after-market companies modify their players with SDI (Serial Digital Interface) that professionals use to move digital video data through equipment circuits. DVDCCA jumped on and added exemptions for the digital output rule for devices that used either DTCP or HDCP (abbreviations defined below). So with the OK to have digital output on DVD, the ball got rolling. Two formats were created for high bandwidth digital video and audio, IEEE 1394 a.k.a. “Firewire” and Digital Visual Interface [DVI]. Optical Cable (Fiber), e.g., Toslink, has a high enough capacity (gigabytes per second), but the costs of the electronics required to achieve that capacity has prevented it from becoming a viable solution for consumer grade electronics.
IEEE 1394a (Firewire)
With a maximum capacity of 400 Mb/s, Firewire can’t handle uncompressed HDTV content over 480p. Firewire does have the advantage that the protocols it uses were designed to be two way, to allow control in both directions, and carry digital audio. You will soon see consumer goods using a common control format for the home theater. No longer will you need 10+ remotes. Connectivity is guarded with the DTCP encryption protocol.
DVI was developed by the Digital Display Working Group (DDWG) and has been chosen by the industry as the digital video connectivity solution. With a maximum capacity of 1.65 Gb/s per TMDS link (3 data channels per link, 2 links possible per connector), DVI is just right for high resolution video. The new(er) standard affords digital audio as well. The DVI connector also allows for an analog connection. There are DVI display devices on the market now, with more on the horizon. Dish network and DirecTV both have products that incorporate DVI. Connectivity is guarded with the HDCP encryption protocol. DVI also allows manufacturers to place images over the content, such as menus and directories. I would venture to say that DVI-enabled DVD players will appear at the end of this year.
Figure 3 - Bandwidth requirements for uncompressed video transmission.
You will see two connectors on the back of the new HD-DVD players: Firewire and DVI. The Firewire connection will handle all the control functionality and audio to the receiver, while DVI will carry the uncompressed video to the display device. It’s possible that Firewire may carry the compressed video feed to the display device, but this means a lot of work for the display device, and added cost, as the DVD player already has the decoding internals.
Some of the new displays that have arrived on the scene are Digital. By digital I mean that the picture that is generated by the display device is created by turning individual elements of the screen on and off by way of a digital code. There are 3 types of digital devices currently on the market. These devices come in different formats such as projectors, rear projection TV’s and direct view displays:
(1) Texas Instruments DLP: A Digital Micromirror Device (DMD) chip has about a million tiny mirrors that reflect the light to create a digital image. This is perhaps the best digital picture available.
(2) Liquid Crystal Display (LCD): Light is projected through LCD panels. The individual LCD elements are turned off and on to create separate Red, Green, and Blue images that combine to produce the image. The Direct Drive Image Light Amplifier (DILA) is included in this category, although LCD is transmissive, while DILA uses a reflective surface behind the panel so that light first passes through the elements, then is reflected, and then passes through the elements again on its way to the lens. LCOS (Liquid Crystal on Silicon), owned by Hitachi, Korea, is similar to DILA, owned by Victor Corporation of Japan, a.k.a. JVC. DILA has a fill-factor of 93%, DLP is 88%, and LCD is 83%. Fill-rate means how much of the image is actually made up of light produced by the elements, as opposed to the space in between the elements.
(3) Plasma: A plasma screen is
composed of millions of tiny chambers that contain Noble gases such as Argon,
Neon, or Xenon, and when current passes through them, they emit red, green, or
blue light, to make up the image on the screen. This is like the technology of
Neon signs that we see everywhere, such as on restaurants, except that the
plasma screen has millions of them instead of just one. The emission of the
colored light is a discharge produced when the applied electric current pushes
electrons in the gas atoms to a higher state, and the electrons then jump back
to their original positions. The difference in energy states between the two
electron positions is given off as light of specific wavelengths (colors).
To achieve the best picture you would want to use a digital signal with these devices. If you use an analog signal you will always lose some of the picture quality to conversion loses. Since the content we are displaying comes from a digital source it would actually take LESS WORK and LESS ELECTRONICS to send the digital information to the display device. So why are we being forced to use analog conversion on our display devices? The content providers.
Protecting Digital Content
Almost everyone is familiar with the effects of copy protection. In 1984 the Supreme Court ruled that it was legal for home consumers to record broadcasts onto tape. This started the war between the Content Providers and the Consumer. In 1998, the Digital Millennium Copyright Law (DMCA) was passed, prohibiting consumers of circumventing content protection, or reverse engineering it.
There are two areas of encryption: content and
transport. DVD is a content medium, where DVI is a transport. However, as we all
know, every type of encryption can and will be broken, given enough time. So, it
seems to us a tremendous waste of time and money to create the protection scheme
in the first place. The average consumer would not attempt to copy and sell
digital movies. For the small percentage of people out there who intend to do
just that, they will break the copyright protection code, copy movies, and sell
them. It is going to happen. Period. It will take the movie pirates less time to
crack the code than it took the studios to create it.
Content Scrambling System (CSS)
CSS was created to protect the information stored on DVD discs from being copied. It effectively scrambles the MPEG-2 video information to a point where it is unviewable. The algorithm and keys required to decode the disc are stored on the DVD player. When you play a DVD, the player decodes the disc and hands the information to the transport. In November, 1999, the CSS encryption was cracked, making it possible to extract the digital version of the information stored on a DVD. The Motion Pictures Association of America (MPAA) sued to keep this information from the public. Later, they became the biggest supporters of the DMCA.
Digital Transmission Content Protection (DTCP)
DTCP was defined as a method to encrypt information being sent over the IEEE 1394 transport to another device. This information can be audio or video or both. This encryption scheme has been adopted by major manufacturers and will become the standard by which Firewire connectivity is defined in the home theater. Note: HDCP was recently adopted by the DTCP group. Its specifics follow the DTCP section.
DTCP allows the creation of a set top box (STB) that decodes the digital information. In order to create such a device it must adhere to the following outputs:
DVI with HDCP. This is defeating the purpose of DVI, as the limit of Firewire is 480p.
Standard Definition TV (SDTV) Analog:
NTSC with Macrovision
Composite with Macrovision
S-Video with Macrovision
Component Interlaced with Macrovision-DVD and CGMS-A
Component Progressive (480p) with Macrovision-DVD
HD Analog (Constrained to 480p)
HD Analog (Non-Constrained)
Only if flagged by content provider as Copy-Freely or Non-Constrained Analog
DTCP licensed Products (Only DVI at this time)
Personal Video Recorders
Must recognize the Copy Protection flag
Cannot store material marked as “Copy Never” for more than 90 minutes after receipt
High Bandwidth Content Protection (HDCP)
While DTCP defines an encryption standard for 480p and below, what about true HDTV (720p and 1080i)? Intel and other manufacturers defined the HDCP standard of encryption to support huge amounts of bandwidth. HDCP is defined over the DVI transport, allowing HDTV transmissions to include 1080p. Where DTCP allows a set top box for legacy devices, HDCP requires that the decoding take place Iin the display device. Here is a brief overview:
Establishes encrypted link from player to display device, only a routing/switching device is allowed between
All decoding of material must take place in the display device, no external converters
Can carry a digital audio feed as well
Connector allows for an analog connection
Unfortunately for consumers, the new encryption schemes mean that if you have purchased a display device before the fall of 2002, there is a 90% chance that you will not be able to watch digital HDTV media on your display. Unless your device has a DVI HDCP connector on it, you will be limited to a 480p analog signal (or a 480p digital signal if you have DVI DTCP connector) from digital sources, including HD-DVD, HD Satellite, and HD-Cable. There are a few content sources now that provide 1080i analog, but they can't offer the digital connections on the same unit per the license agreements. Expect to see these 1080i analog devices disappear fast, because the studios consider them a threat. They probably consider all 50,000,000 computer jocks in the world a threat for that matter. And for good reason.
Before you get mad at the salesman that sold you that $12,000 HDTV or $50,000 plasma, keep this in mind; the salesman probably didn’t know. The electronics industry kept this secret under wraps as long as they could. After all, who would buy a HDTV device if they knew it would be obsolete in less than 2 years? But, just because it has a DVI input doesn’t mean it supports HDCP, so check before you buy!
You should be mad at the studios! Unfortunately, the studios don't care, although they should. They know very well that the average consumer doesn’t make a living copying digital media. Those who do make a living copying digital content have always found a way to crack or get around the content protection schemes. In fact, HDCP has already been cracked. We think the problem is not about money. It's about power. The studios want to have absolute control over their content, even at the expense of consumers losing faith in their industry and losing sales. The beauty is that they will lose all of these things . . . control, credibility, and money, because consumers are smarter than the studios are. Do the studios think that consumers are vindictive? No. Are consumers vindictive? You bet. Note to the studios: Just watch us.
HDTV is not really new. It has been around since
1981. But, the studios have restricted the release of digital media until they
felt that they could have sufficient control over it, a control that will never
be possible. This control has not nor will it ever “protect” the consumer’s
interests, only the studios. In fact their implementation of these restrictions
will cause major consumer backlash as we all see what has transpired, and how
much it has cost us. If anything, the deceit and confusion over DVI and DTCP
will only make the adoption of HDTV and HD-DVD
The MPAA knew what they were doing when they designed
the requirements for the HDCP and DTCP standards. Their efforts in reducing
digital theft have caused their consumers undue financial hardship. The MPAA
knew full well that they were creating standards that would be incompatible with
the current install base of HDTV, representing millions of consumer dollars, and
intentionally doing so.
1. The DTCP standard should be modified to allow full HDTV resolution on analog outputs for 10 years. This will allow the current crop of consumer equipment to be used to end of life with digital compatibility.
2. The HDCP should be amended to allow for equipment to decode from DVI to full resolution HDTV on analog outputs for 10 years.
Table of Abbreviations Used in this Article:
DVD - Digital Versatile Disc
HDTV - High Definition Television
SDTV - Standard Definition Television
CCP - Commercial Content Protection
SMPTE - Society of Motion Pictures and Television Engineers
FCC - Federal Communications Commission
DVDCCA - DVD Copy Control Association
MPAA - Motion Pictures Association of America
CSS - Content Scrambling System
SDI - Serial Digital Interface
DVI - Digital Visual Interface
DTCP - Digital Transmission Content Protection
HDCP - High Bandwidth Content Protection
DLP - Digital Light Processor
DMD - Digital Micromirror Device
LCD - Liquid Crystal Display
LCOS - Liquid Crystal on Silicon
DILA - Direct Drive Image Light Amplifier
DMCA - Digital Millenium Copyright Law
STB - Set Top Box (digital TV decoder box)
Places for More information:
Digital Transmission Licensing Administrator (creators of DTCP): http://www.dtcp.com/
Contact: mailto::firstname.lastname@example.org?subject=DTCP and it's implications to consumers
Digital Content Protection LLC (creators of HDCP): http://www.digital-cp.com/
Contact: mailto:email@example.com?subject=HDCP and it's implications to consumers
Motion Pictures Association of America (MPAA): http://www.mpaa.org/
A Cryptanalysis of the High-bandwidth Digital Content Protection System by Scott Crosby (CMU): http://www.star-lab.com/sander/spdrm/papers/crosby.pdf
Convergence Technologies http://www.planetee.com/planetee/servlet/DisplayDocument?ArticleID=6968
Gas discharge spectra (plasma screens) http://home.achilles.net/~jtalbot/data/elements/
DVD Copy Control Association (DVDCCA): http://www.dvdcca.org/
- Brian Weatherhead -
© Copyright 2002 Secrets of Home
Theater & High Fidelity
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