20
Aug/09
0

HDCP in detail

High Definition digital video allows users to experience high resolution, near perfect video content. Asmore content is delivered digitally, the content creators are increasingly concerned with content piracy because digital content can be perfectly duplicated. Therefore anti-piracy safeguards such, as High Bandwidth Content Protection (HDCP) is necessary in order for original content creators to protect their assets. In this article we will touch on the key points of HDCP.

What is HDCP

High-Bandwidth Digital Content Protection,HDCP, is an encryption scheme developed to defend against uncontrolled copying of digital content over high bandwidth digital interconnects such as DVI and the HDMI. The FCC approved HDCP as a “Digital Output Protection Technology” on August 4th,2004. A HDCP protected system consists of: 1) HDCP transmitter(DVD player for example), 2) the digital interface (DVI orHDMI), and 3) the HDCP receiver (your display monitor). Inbrief, the content is encrypted at the transmitter and the signal is passed to the HDCP receiver (display) via the DDC lines (in essence an I2C bus) where it is decrypted before viewing. HDCP requires that both the transmitter and the receiver comply with standards. If either one does not comply,the video will not be displayed properly. Incidentally, HDCP does not apply to analog interface such as component video although component video can be used to display high definition video.

Why should the consumer care about HDCP

It is highly recommended that consumers be aware of HDCP and purchase sets that are HDCP compliant. Here is why. It has been speculated that the two competing high definition DVD standards HD DVD, and BLUE RAY, due out in 2006 will only deliver full resolution on HDCP protected outputs such as HDMI or DVI. If true, then usersmust have a HDCP monitor in order to experience full resolution HD DVD technology. Therefore it is prudent for the consumer to select HDCP compliant displays so the display can be used with future applications.

What is involved during a HDCP session

HDCP is a complicated process but can be broken down to 3 key functions: Authentication, Encryption, and Renewability

Authentication:

The first step before video is actually sent is for the HDCP transmitter to determine if the receiver is “authorized” to accept HDCP protected content. Stored in the PROM of each transmitter and receiver is an array of 40, 56-bit secret keys and a 40-bit entity called Key Selection Vector. Authentication requires that the transmitter and receiver pair exchange “secret keys” and key selection vectors. The keys are scrambled and never revealed. The mathbehind the encryption allows each half to calculate a resultant number, call it Rs, based on the key exchanges. The Rs value is then shared and compared. If the Rs value matches, the receiver is accepted as an authorized HDCP receiver and video transmission can start.

Encryption/Transmission:

Once authentication is completed, transmission of the video content can commence. To prevent an unauthorized receiver from receiving the content, the video data must be encrypted prior to transmission. At the transmitter end, the video data bits are exclusive-ored with ashared calculated number lets call it Rt ( Rt is similar to howRs was calculated) and sent to the receiver. At the receiver end the encrypted data is again exclusive-ored with Rt. Since the XOR function is invertible, XORing with the same Rt at the receiver end will reveal the true unscrambled video bits. Incidentally, a new Rt value is calculated about every 2 secondto prevent corruption due to hacking.

Conclusion

HDTV technology is changing rapidly. Content providers need to protect against piracy by implementing HDCP. HDCP and digital connection standards such as HDMI will become the de facto standard for digital video connections. We have outlined the important features of HDCP, so the consumer can make intelligent purchasing decisions.

14
Aug/09
0

The Truth About Monster Cable, Part 2 (Verdict: Cheap Cables Keep Up…Usually)

This time, we brought along a bag full of awesomely priced cables, mostly from Monoprice, that we were ready to run bandwidth tests on, side-by-side with Monster’s finest (and most damned expensive) cables.

What were our findings?

1) At short distances up to 6ft (2 meters), you can pretty much get away with any cable. Monoprice cables kicked ass at the 6 foot length that mostly everyone uses.

Not all cables are the same, however, and in truth, it’s the medium-priced cables that may be the real rip-off.

2) At longer distances, cheaper cable tends to choke up. A 720p signal will make it, but even today’s standard 1080p signal can fry out inside of a long cable that isn’t built as well. If you are trying to hook up a 1080p projector on your ceiling to a Blu-ray or HD DVD player, this is a concern.

The tests, which fired digital signal through the cable to synthesize high-definition video, can be divided into REAL-WORLD requirements (720p and 8-bit 60Hz 1080p) and FUTURE-WORLD requirements (12-bit 60Hz 1080p and even 12-bit 120Hz 1080p). Mind you, the future formats don’t exist now, so they should only be a concern when you are buying cables you intend to keep for five years, such as those you want to build into a wall.

To simulate high-def video, it sends signal down one of three paths within an HDMI cable, so its signal at any given time is ONE-THIRD the bandwidth of that video format. The list of bandwidth tests we ran is as follows:

REAL WORLD
• 720p 8-bit 60Hz = 742 Mbps (x3)
• 1080p 8-bit 60Hz = 1.65 Gbps (x3)

FUTURE WORLD
• 1080p 12-bit 120Hz = 4.455 Gbps (x3)
• 1440p 12-bit 120Hz = 8.24 Gbps (x3)

When the signal was sent out over the cable, its performance was measured on a Tektronix DSA8200 Digital Serial Analyzer. The argument goes like this: it may all be 1’s and 0’s, but what is being sent over that cable is electric current. When too much data is sent over a shabby cable, the device on the other end can’t tell what is a 1 and what is a 0. The end result is video that is either jittery, full of digital snow, or flat-out not there.

The Tektronix display shows two arcs, a high ridge that stands for the 1’s and a low ridge that stands for the 0’s. As bandwidth increases, you will see that the arcs get fuzzier, and at the failure point, there are too many 1’s that look like 0’s, and vice versa.

Bear in mind, in some cases, if the cable failed at one level, we didn’t go on to the next. Likewise, if we knew it passed the higher test, we might not go on to a lower test.

even the Monster 10-meter couldn’t pass the Future World 1080p test. The Monster folks said they didn’t have a 50-footer in the building that they could test with, but I suspect it would have done a little bit better than the Monoprice, possibly even carrying today’s 1080p. But we did not test that.

Judging from these results, I would have to reiterate my original position, that it’s best to skimp at short distances, but you don’t want to be caught with the wrong cable installed in your walls. Even with the projector, it might be smart to buy a $30 cable first and see if it works, but be prepared, when upgrading your gear, to upgrade the cable too. Does it have to be Monster? Hell no, but you might have to pay something close to a Monster-sized price.

The truth is, the bigger rip-off appears to be the $20 XtremeHD cable. It didn’t perform as well as stuff one-fifth the price. (No wonder they don’t sell a 10-meter cable.) I would say beware of mid-priced cable of dubious origin. Our dealings with Monoprice lead us to believe that at least they know what they’re selling, even at such a tremendous discount.

Stay tuned for HDMI Cable Battlemodo: The Truth About Monster, Part 3, where we try to match the laboratory results with basic, in-home testing. If the Digital Serial Analyzer said a cable fails, but it works just fine in my basement, maybe I’ll have to call BS. – Wilson Rothman

12
Aug/09
0

Difference between 1080i and 1080p

While high definition has become a reality for many consumers, the technical jargon associated with this exiting new technology is causing much confusion. Just as we were beginning to understand the differences between Blu-ray and HD DVD along comes a new high-definition format, 1080p.

But why do we need another high-definition format anyway? Many of us have bought our HD Ready screens and were ready to sit back and enjoy this new viewing experience, but now we are all wondering if we bought the right kit in the first place.

Many of the more recent HD Ready flat screens feature a resolution of 1,366×768 pixels. This will display the commonly used 720p and 1080i formats, although 1080i/1080p signals will be downscaled to fit. To display 1080i/1080p signals in their entirety, you’ll need a screen with a resolution of 1,920×1,080 pixels, coined ‘Full HD’ by the marketing men.

However, just because a screen has 1,920×1,080-pixels it does not necessarily mean that it will accept 1080p input – so check before you buy.

Remember, 720p, 1080i, 1080p are formats in which ‘Sources’ of high definition content are presented for viewing on a particular output device such as your LCD/Plasma screen. The source could originate from your TV cable provider for example, or your xbox 360. To restate the point, 1080i/1080p needs a screen resolution of 1,920×1,080-pixels to display in its entirity, but you don’t have to have a screen with this resolution to display a 1080i/1080p signal – lower resolution screens downscale the signal to fit.

Taking a step back, 720p and 1080i were initially set out as the two key standards for High Definition content, with Sky HD, HD DVD and the Xbox 360 supporting these formats. Any TV that supports 720p and 1080i is classed as HD Ready. Let’s take a step back for a moment and take a quick look at the development of TV technology to see how we arrived at these standards.

In a CRT display (the TV you grew up with), a stream of electrons is generated by a gun, and is scanned across the face of the tube in scan lines, left to right and top to bottom. The face is coated in phosphors, which glow when hit by the electron stream. A method of scanning was required that would reduce the transmitted TV picture’s bandwidth and work in accordance with the electricity supply frequency (50Hz in the UK and Europe and 60Hz in the US). The result was interlaced scanning.

A method of reducing bandwidth was required because early sets were not able to draw the whole picture on screen before the top of the picture began to fade, resulting in a picture of uneven brightness and intensity. To overcome this, the screen was split in half with only half the lines (each alternate line) being refreshed each cycle. Hence, the signal is interlaced to deliver a full screen refresh every second cycle. So if the interlace signal refreshes half the lines on a screen 50 times per second this results in a full screen (or frame) refresh rate of 25 times per second. The problem with interlacing is the distortion when an image moves quickly between the odd and even lines as only one set of lines is ever being refreshed.

As TV screen technologies have progressed another system called Progressive Scan has also been developed. With progressive scanning the frames are not split into two fields of odd and even lines. Instead, all of the image scan lines are drawn in one go from top to bottom. This method is sometimes referred to as ’sequential scanning’ or ‘non-interlaced’. The fact that frames are shown as a whole makes it similar in principle to the way film is shown at the cinema.

At this point it is worth considering what we mean by resolution in relation to TVs;

Resolution: HD-Ready TVs need to be able to display pictures at the resolution set by the new standard. Resolution can be described either in terms of “lines of resolution,” or pixels. The resolution you see on your TV depends on two factors, namely the resolution of your display and the resolution of the video signal you receive. Because video images are always rectangular in shape, there is both horizontal resolution and vertical resolution to consider.

Vertical resolution: This is the number of horizontal lines that can be resolved in an image from top to bottom. The old familiar CRT TV displays 576 lines, while Digital HD television operates at a resolution of either 720 or 1080 lines. This is the most important resolution as it is most noticeable to the human eye.

Horizontal resolution: This is the number of vertical lines that can be resolved from one side of an image to the other. Horizontal resolution varies depending on the source. The number of horizontal pixels is not quite so critical as vertical resolution as it is not as obvious to the human eye during normal viewing.

An analogue TV signal in Europe, where the PAL standard is used, has 625 horizontal lines of which 576 lines are displayed and the image (or frame) is refreshed 25 times a second. This is the standard we have been used to for years.

A High Definition Digital TV signal delivers significantly more picture detail and audio quality than a standard signal, producing pictures that are significantly better, sharper and clearer;

720p: 1,280×720 pixel resolution. High-definition picture that is displayed progressively. Each line is displayed on the screen simultaneously, therefore it is smoother than an interlaced picture.

1080i: 1,920×1,080 pixel resolution. High-definition picture that is displayed interlaced. Each odd line of the picture is displayed, followed by each even line, and the resulting image is not as smooth as a progressive feed. 1080i is therefore a more detailed picture suited to documentaries and wildlife footage, but less suitable for action-oriented material such as sports and movies.

1080p: 1,920×1,080 pixel resolution. High-definition picture that is displayed progressively. Each line is displayed on the screen simultaneously, therefore it is smoother than an interlaced picture. This is the ultimate high-definition standard — the most detailed picture, displayed progressively.

There are two main formats for HDTV, namely 720p (i.e. a 720 line picture progressively scanned 50 times a second) and 1080i (1080 lines interlaced at 50 cycles per second). The picture resolution of a high definition digital TV is about 4 times greater than a typical 576 line TV picture.

not having a screen which is able to display 1080p may not be important to you. However, there are exceptions, and if you are a serious game player you will probably already know one of them, or to be precise two of them. The xbox360(with a little tweak) and the  playstation 3 produce output at 1080p. Also, the new High Definition DVD format, blu-ray has also been designed for 1080p ouput. Is the difference worth the extra investment? Maybe, something you will have to judge for yourselves …