High Definition Facts

High Definition Facts

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High Definition Facts

If you follow tech news, you’ve probably heard about High Definition movies and the two competing "shiny disc" formats -- HD DVD and Blu-ray -- and the new copy-protection system, AACS. Unfortunately there is a lot of misinformation out there about these technologies, probably because the facts change over time and the press essentially plays a game of telephone with each story repeating "facts" found in an earlier story.

Whilst this post won’t go into great details about either of the disc formats, it will talk about a few key things they both have in common. Thanks to other members of the HD DVD team here at Microsoft for providing some of the more esoteric information :-)

Maximum Resolution

Both formats support (up to) 1920 x 1080p content. Some news stories claim that HD DVD only supports 1080i, but that claim is false. Additionally, both formats support a wide variety of framerates, including 1080p24 (24 frames per second) which is the native frame rate of film and the most accurate way to store motion picture content. Players (in both formats) may choose to output at 1080i for various reasons -- component cost vs. small number of 1080p-capable displays; etc. -- but the content on the disc will almost certainly be at 1080p24. Given that many present-day TVs can only accept 720p or 1080i input anyway, this is not such a big deal for consumers who already purchased "HD-ready" TVs. In time, as they upgrade their TVs to 1080p they can also update their players to 1080p and take advantage of lower price-points at that time. Some displays can also convert the 1080i signal back into a 1080p signal for final display.

Of course, it is up to the Studio to decide which resolution to use on the disc, but it would be hard to imagine them choosing anything other than the native frame rate of film, which will give the very best picture.

Copy Protection

Both HD DVD and Blu-ray support the AACS copy protection system, which is based on standard cryptographic algorithms and is published on the AACS LA web site. Blu-ray supports an additional copy-protection system named "BD+" that is based on reading a small program off each Blu-ray disc and running it to ensure the player is compliant. Not much is known about how this works, although you can find some basic information about SPDC. Blu-ray also includes a third system named "ROM Mark" that makes it hard to duplicate entire discs.

In theory it is up to the Studio to decide if they want to protect their content or not, but in practice... well, you can figure that out for yourself :-)

(Side note: Since all HD DVD players will play standard DVDs as well, they will support the older CSS copy-protection system).

Down-Rezing

"Down-rezing" is the act of taking a full 1920 x 1080 image and converting it into a 960 x 540 image when the image is output over unprotected analog connections (eg, component video). This is one quarter of the total resolution of full high-definition, but still 50% more than a 720 x 480 standard-definition picture. Down-rezing is controlled by the Image Constraint Token -- or ICT -- as defined by AACS and is enforced by both formats. ICT does not apply to HDCP-protected digital outputs.

Again, it is up to the Studio to decide whether they want to assert ICT or not on any particular disc, and many studios have announced that they will not do so. Any discs (in either format) that asserts the ICT will contain product labelling to inform customers that they will not get a full HD picture over unprotected outputs.

Digital Only Token

The Digital Only Token -- or DOT -- is also defined by AACS (and will be enforced by both formats) and is even stronger than the ICT. If a player detects the DOT, it must not allow any output over unprotected connections; only HDCP-protected digital outputs will be supported. Users will see a blank screen if they try to watch a DOT movie over unprotected connections.

In the future, it will be up to the studio to decide if they want to assert DOT on any particular disc or not, but for the time being studios are not permitted to use the DOT. This means you won't see any DOT-enabled titles for some time, and right now we don't really know what the DOT will be used for (other than "New Business Models" which may be entirely dissimilar to traditional consumer products purchased at retail).

Extra Geeky Info

HD DVD encodes audio and video in Program Streams and uses field syntax with 30 frame per second timing to represent both 30 fps interlace and 24 fps progressive content. “Missing fields” for 24P content are replaced by “repeat field flags”, the same as DVD-Video. Decoders can ignore the “flags” to output P24 or use them to output 30i. Blu-ray encodes audio and video in Transport Streams and has the option to use frame syntax to encode 24fps content with 24fps timing.

 

  • Good stuff. Thanks.

    Do you know anything about the alleged Blu-ray capability for discs to "upgrade" your player's firmware without the user's consent?
  • I hope ICT will produce a higher resolution than that in PAL regions, for PAL DVD has 576 lines, not 480. It would be somewhat embarrassing for them if the new standard were actually worse, for most people, than the current one!
  • Jeroen -- I don't know about that, sorry. Maybe Howard Stringer has a blog? :-) Or you could try www.avsforum.com

    Mike -- Hmmmm, let me see if there's any info here on that.
  • It turns out that ICT will be the same resolution everywhere, since AACS defines ICT and AACS does not recognise region codes.

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           A lot of consumers are under the impression that higher-resolution images are the...
  • I have a question: What are the framerate and size constranints? Is 1500x750 video possible, for example? Or it's like DVD, where you can only have 720/704/352 "columns"? And what's the maximum framerate? Is 1280x720x60fps progressive supported? And 1920x1080px60? And arbitrary framerates (for example 45fps, even if it looks bad in TV)?

    Also, if it's not a secret (although I realize it's a complex question), what's the file layout on the disk? More specifically, what's the container? MPEG-TS? ASF? MP4? ...

    Thanks a lot :)
  • Isn't that true that blu-ray does 1080 60p and HD-DVD only 60i or 30p  (half the info, half the bitrate) ?? That's what I read in the new edition of "DVD Demystified"?

    It's true that there is not a lot of 1080p tv set, but it's the future. 1080 60p is an HD standard, so it's better to be ready for it, no ??

    It's seems that the reason is that HD-DVD has a maximum bitrate of 29Mbps, and Blu-ray 45Mbps (from what I recall). Is that true ??
  • Anon - That's not my area of expertise, but I'll see if anyone else around here will anwser it. I wouldn't be surprised if you were limited to a set of "standard" resolutions though (like 1920 x 1080 and 1280 x 720 with maybe 720 x 480).

    Video is stored in a file called an EVOB (enhanced video object); you should get the HD DVD spec if you want the details :-)
  • Faz: HD DVD does 1920 x 1080p. The early Toshiba player only does 1080i, but then so will the low-end PlayStation 3. It's mostly a question of economics. The content on the disc is in 1080p and will be ready when a player wants to display it.

    Max bitrates are not my specialty, but for watching a movie in an advanced codec like VC-1 both formats have more than enough bandwidth. Just look at the HD DVD titles out right now; they are absolutely gorgeous!
  • The max frame rate of video content on HD DVD and Blu-ray are both 60p for 1280x720, or 60i for 1920x1080.  1080p60 is actually very rare -it isn't part of the ATSC spec which defined today's HD display technologies.

    There are only a few supported standard resolutions.  All the titles today are 1920x1080.
  • Also, as for 1080p, it's 24p, with 3:2 pulldown added.  Most modern sets will be able to perfectly reverse the 3:2 pulldown, and display in progressive.  Having a progressive player wouldn't meaningfully improve video quality, even on a high end display.
  • Thanks for your reply. I did get the spec and found out about resolution and framerate support. The following images sum it up (if they are allowed here):

    http://img396.imageshack.us/img396/5555/hddvdntsc2vk.png
    http://img50.imageshack.us/img50/8894/hddvdpal1af.png

    (I didn't found out about EVOB, thanks for your pointer!)

    Unfortunately what Faz said seems true: HD-DVD supports 1920x1080 up to only 30 frames per second, so you can get 30p or 60i (60 fields per second, half the pixels of 60p, which is 60 full frames per second). At 1280x720, 60 frames per second are supported enabling 60p.

    (Of course a player can output 1920x1080x80p, but it'll have to either deinterlace or present each frame twice, fabricating half the pixels)

    As the tables above point out, you are limited to a certain set of resolutions, but that isn't much of a problem since resizing can be done at high quality, should it be required.

    The real disappointment for me is PAL territories getting 25/50fps for HD resolutions too. I had hope HD would end that and support for 24, 25, 30, 50 and 60 fps would be mandatory, but now we'll still have problems (converting 30 to 25 can't be done easily and quality is rarely optimal). I don't understand why is this since monitors/TVs do support a wide range of refresh rates, if you feed them an "illegal" signal such as PAL with 60fps they display it correctly (video game consoles have a PAL60 mode).

    Oh well, you can't have everything :)
  • Development Resources Introduction to HD DVD Authoring Getting Started with HD DVD (includes link to

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