Friday, June 12, 2009
Once you decide to go Blu-ray, you are confronted with a welter of confusing features that some players and discs offer, and others do not. For instance, if you look at this list of available Blu-ray Discs at Blu-rayStats.com (click on the image below to see the list)
you see a table listing all the Blu-ray Discs yet issued, some 1,552 as of this writing. There are columns labeled "BD Java," "Pic in Pic," "Bonus View," and "BD Live." What do these mean?
In plain language, these have to do with whether a Blu-ray player, playing a Blu-ray Disc as opposed to a DVD, can do certain things: provide interactive menus that "pop up" over disc content; handle "picture-in-picture" video and audio content that plays over top of "regular" disc content; and/or access additional disc content that resides on the Internet, not on the disc.
All of these are optional disc features that, in order to work, have to be supported by capabilities in the player. Not all players support all the features, and not all discs contain all the features. Many Blu-ray Discs have none of these features.
In general, the later the date a model of Blu-ray player was introduced, the more likely it is that all of these disc features are supported. However, some older players can have their onboard firmware updated to support disc features not originally supported at the time the model was introduced ... as long as those players have all the necessary hardware.
Here's a rundown on the features and the computer language which supports them:
BD-Java: All of these features utilize the BD-Java computer language that is geared especially to Blu-ray. BD-Java is also called BD-J, or Blu-ray Disc Java. Basically, it's a programming language that all Blu-ray players support, in some version. Blu-ray players are actually (in addition to being able to play Blu-ray Discs) a kind of computer that runs BD-Java, and Blu-ray discs optionally take advantage of that.
Blu-ray discs that take advantage of BD-Java and the features it supports have to be "authored in BD-Java," which means they possess a different file structure on the disc than they would if they were just "ordinary" Blu-ray Discs that are not authored in BD-Java. Disc "authoring" is, simply, how the various pieces of information that are recorded on the disc are put together by the creators of the disc. Blu-ray discs are authored using files. Much like files on your computer, these files exist in a folder hierarchy on the disc. Blu-ray players, needless to say, hide the file structure/folder hierarchy from user view.
On the Blu-rayStats.com page mentioned above, discs that are authored in BD-Java are shown with a "Yes" under BD Java.
Interactive "pop-up" menus: BD-Java disc authoring opens the door to several user capabilities. One is simply the ability for a disc to provide interactive "pop-up" menus. Blu-ray Discs that are not authored in BD-Java must get by with "dumb" menus like those on DVDs, which really aren't "smart" or interactive and can't pop up while the disc continues to play. But Java-authored Blu-ray Discs can have truly interactive pop-up menus that use the BD-Java computer language and file structure.
Here is an example of a pop-up menu:
Not all Java-authored discs provide pop-up menus. Just because a disc is authored in BD-Java does not mean pop-up menus exist on the disc.
Nice as interactive pop-up menus are, most or all Blu-ray Discs which use pop-up menus unfortunately do not allow a Blu-ray Disc player to automatically resume a movie from any arbitrary point in the middle of the movie where the movie was stopped. This is a feature we are used to on DVDs and DVD players, and Blu-ray players also support it on those Blu-ray Discs that don't have pop-up menus. But there is something about discs with BD-Java pop-up menus that prevents this feature from working.
Blu-ray profiles: Every Blu-ray player supports BD-Java — and thus, at a minimum, pop-up menus — but there are three different levels, or "profiles," at which BD-Java support may be included in a playes, depending on when the player model was introduced.
Profile 1.0: The first level of BD-Java support is called Profile 1.0. All Blu-ray players, however early they were introduced, support Profile 1.0 of BD-Java, which is what allows discs to have pop-up menus. (Again, not all discs in fact have interactive pop-up menus, but all players support them if they are in fact present on a disc.)
Profile 1.1: The second level of BD-Java support is Profile 1.1, which has also been dubbed "Bonus View" or "Final Standard Profile" (though it isn't actually final). Profile 1.1 does what Profile 1.0 does — mainly, pop-up menus — plus adding the ability to play a "picture in picture" (PIP) as a secondary audio-video stream from a Blu-ray Disc that is programmed to show one.
If you can see a small window of (say) video commentary on the TV screen, where a director or actor talks about a scene being shown in the background, you may be seeing Bonus View in action. Here is an example from a German Blu-ray title, Neues vom Wixxer:
Blu-ray Discs that offer Bonus View are shown on the Blu-rayStats.com page with a "Yes" in the Bonus View column. If you invoke the "Has Bonus View" filter, you will see just the releases with Bonus View — 106 as of this writing. You can play these releases on Profile 1.0 players, but you can't access the Bonus View content.
Keep in mind that some Blu-ray Discs have been issued with PIP implemented by means of a second whole copy of the movie that is recorded separately on the disc with an inset audio-video program over top of the main picture. This is not Bonus View.
Bonus View-compatible players need to have additional hardware, above and beyond that required for Profile 1.0 players: 256 MB of "local storage" — a.k.a. "persistent storage" — such as flash memory or a hard drive (none was required for Profile 1.0); plus secondary video and audio decoders. If a Profile 1.0 player lacks these extra items, it can't be upgraded to Profile 1.1 via a simple firmware upgrade.
Blu-ray Discs that offer picture-in-picture content are shown separately on the Blu-rayStats.com page with a "Yes" in the Pic in Pic column. If you employ the "Has Bonus View" filter on that page, you can see that all Bonus View discs are "Pic in Pic" discs. However, there are some "Pic in Pic" discs that don't Bonus View ... and some that don't even use BD-Java.
For example, the movie "Blow" is shown as "Pic in Pic," but not as either "BD-Java" or "Bonus View." These discs don't use BD-Java, and they implement PIP with a second whole copy of the movie.
The movie "The Contract" is shown as having "Pic in Pic" and "Bonus View," but not as having "BD Java." That makes questionable sense. To the best of my understanding, Bonus View requires BD-Java.
Profile 2.0: This is the third (and supposedly final) level of BD-Java support in Blu-ray players — for videos, that is; there is a Profile 3.0 in the works for BD-Audio use.
To the capabilities of Profile 1.1/Bonus View/Final Standard Profile and of Profile 1.0, Profile 2.0 adds an Internet connection via an Ethernet port and/or via a wireless 802.11 (WiFi) adapter. This connection allows players to honor certain Blu-ray Disc titles' ability to access online content. The bonus material on the disc is augmented with additional bonus material from the Internet. This Internet-based extra content is "live" — it can change — and so Profile 2.0 is called "BD-Live."
Players that support Profile 2.0/BD-Live add extra "persistent storage," above and beyond that needed for Profile 1.1, with a minimum of 1 GB of storage being present to hold downloaded content and the like.
All the features of Profile 1.1 and Profile 1.0 are supported by Profile 2.0.
Again, a great many Blu-ray Discs don't make use of Profile 2.0/BD-Live. The ones that do are listed in Blu-rayStats.com with a "Yes" under BD Live. As of this writing only 177 are shown, when you invoke the "Has BD Live" filter ... and if you also invoke "Has Bonus View," there are only (as of this moment) 51 Blu-ray Discs released in the U.S. that use both.
Because Profile 2.0/BD-Live requires additional hardware beyond Profile 1.1/Bonus View/Final Standard Profile, unless that hardware happened to be included on a Profile 1.1/Profile 1.0 player, that player cannot be upgraded to Profile 2.0 via a firmware upgrade.
Confusingly, some earlier players that don't support Profile 2.0 do have an Ethernet port. These are strictly for firmware updates and can't be used to access downloadable BD-Live content. Hence, there is no way to upgrade these players to Profile 2.0. (What could they have been thinking?)
Can You Upgrade Blu-ray Discs?
Blu-ray discs have to be authored in BD-Java by their creators and programmed to use interactive pop-up menus and/or Bonus View picture-in-picture content and/or BD-Live content, if those capabilities are to be supported by the disc. (In theory, a disc could be authored with BD-Java and have none of these features.)
Since Blu-ray Discs are read-only, there is no way to "upgrade" a disc to use these features — even if the disc is authored in BD-Java — once the disc is made and is in the customer's hands. Accordingly, a title that was released without BD-Live capability may wind up being re-released in the future with it. The customer who wants to take advantage of BD-Live would have to buy the title a second time, assuming it is ever re-released. (An exception: if a disc includes BD-Live capability in the first place, the online content that it can access can be changed or amplified over time.)
Bookmarks: There is another BD-Java capability that is of interest: the ability for the user to create "bookmarks" that allow any point in a movie that is bookmarked by the user to be returned to at will. A bookmark is sort of like a home-brew chapter stop that the user creates on the fly, usually by pressing a button on the remote, then uses to select where playback of a program moves to or begins the next time the disc is used. A bookmark is sometimes called a "personal scene selection."
I have been unable to discover whether bookmarks officially require any particular BD-Java profile, but they do require that the bookmark capability, which is programmed in BD-Java, be explicitly included on a particular Bu-ray Disc. Hence, only certain discs support bookmarks.
However, I do know that disc-based bookmarks are saved by the Blu-ray player on its "local storage" — which makes sense, since the disc itself is read-only. Since Profile 1.0 does not require the player to have local storage, I assume that bookmarks need a player with Profile 1.1 or Profile 2.0. However, since Profile 2.0 is basically nothing more than the addition of BD-Live online content to Profile 1.1, I assume that all you really need to use disc-based bookmarks is a player with Profile 1.1.
For discs that use "pop-up" menus and accordingly cannot automatically resume playing a stopped disc at the point at which is was stopped, creating and later returning to a bookmark can be something of a workaround to the no-resume-play problem.
Finally, some questions that you may be asking are these:
Why this nasty, arbitrary, incremental approach to advanced disc-and-player features in the Blu-ray world?
Why did the potentates of Blu-ray produce so may player models that can't be upgraded, though they knew from day one what the eventual capabilities of players (and discs) would be?
Why are there, even now, so few Blu-ray Disc releases that take advantage of (any or all of) interactive pop-up menus, Bonus View content, and BD-Live content?
I don't claim to know all the answers, but here are some semi-educated guesses. First of all, for whatever reason, Blu-ray's competitor format HD DVD made it to market, with players and discs, earlier than Blu-ray. Blu-ray was playing catch-up.
And it knew catching up was hopeless if it waited until BD-Java disc authoring and the full set of features it would one day support were mature, fully developed technologies.
So the viziers of Blu-ray rushed their product to market with whatever capabilities were ready to go.
Meanwhile, HD DVD was designed in a dissimilar way, with no full-scale equivalent to BD-Java. So HD DVD could be there "firstest with the mostest," with features like picture-in-picture built in from the get-go.
To add injury to insult, rushing Blu-ray to market meant that the first disc releases could not be on dual-layer discs, since the facilities for manufacturing those discs weren't ready. Hence, single-layer releases were the norm. That's since been corrected. Plus, the advanced video codecs "VC-1" and "AVC" weren't yet supported by disc-mastering facilities, so MPEG-2 (the codec used on DVDs) had to be used. That, too, is ancient history. But for a while, the fact that MPEG-2 doesn't compress video nearly as compactly as VC-1 and AVC (also called MPEG4/h.264) meant that it was hard to shoehorn a movie into a single-layer disc without over-compressing it, harming visual quality. There were a lot of complaints that Blu-ray Discs didn't look as good as HD DVDs.
All in all, it's a wonder the Blu-ray format survived at all. But it did, and today it's alone on the battlefield. HD DVD is dead.
Unfortunately, though, the contortions Blu-ray had to go through to avoid having to run up a white flag have left us with a legacy of confusing profiles and player-and-disc features to contend with, as we try to be smart Blu-ray consumers.
For more on the different Blu-ray profiles, see http://news.cnet.com/8301-17938_105-9808376-1.html. For information about the way content on Blu-ray Discs is organized, "The Authoritative Blu-ray Disc (BD) FAQ" at http://www.emedialive.com/articles/readarticle.aspx?articleid=11392.
Tuesday, June 09, 2009
When I compiled Which Blu-ray Player for You? a year and a quarter ago, in March 2008, the world of home video was just getting used to the idea that one of the two competing high-def disc formats had abruptly emerged as the winner over the other, Blu-ray over HD DVD. Blu-ray as a commercial reality was not yet mature, truth to be told. One reason was the relative dearth of Blu-ray titles, along with their high prices compared with the established DVD format. A second reason was that Blu-ray players were generally super-expensive, and most of them lacked features and amenities that everyone knew were in the offing.
$375.00 - $399.95
Excellent image quality on Blu-ray movies; integrated 802.11n WiFi; Netflix, YouTube, and CinemaNow video streaming; superfast disc loading; plays music, videos, and pictures off a connected USB drive or over network; BD-Live Profile 2.0 compatible; onboard decoding for Dolby TrueHD and DTS-HD Master Audio; 7.1 analog outputs; 1GB onboard memory
but: Costs as much as a Sony PlayStation 3 combination Blu-ray-player and video game machine; CinemaNow doesn't stack up to Amazon Video On Demand.
Most new movies that come out on DVD are being released on Blu-ray on the same day, and studios are gradually releasing BDs (Blu-ray discs) of their popular titles from the past. For a list of upcoming Blu-ray releases, click here. For another list of Blu-ray releases that you can already buy, click here. (A trivia question: what was the first Blu-ray Disc release, and when did it happen? Answer: The Funny Guy Collection (Napoleon Dynamite, Office Space, Young Frankenstein), on May 12, 2006.)
Also, the latest Blu-ray players all have the full complement of features and amenities anyone could expect.
Sony PlayStation 3
$309.95 - $399.99 (40 GB)
In addition to its ability to play PS3 video games: plays BD-Live Profile 2.0 Blu-ray discs; plays DVDs; onboard decoding for Dolby TrueHD and DTS-HD Master Audio; built-in Wi-Fi, 40GB hard drive; 1080p/24 video output via HDMI 1.3; upconverts DVDs to 1080p; networking via Ethernet or WiFi
but: No bitstream Dolby TrueHD or DTS-HD Master Audio output; ease of use requires separate purchase of Sony Bluetooth-compatible video remote; glossy black finish is a fingerprint magnet
I've been piping a high-def picture from my Sony PlayStation 3 game console/Blu-ray player into a Samsung 52" 1920x1080p "Full HD" LCD HDTV since late last year, and I can attest that until you've seen a movie in Blu-ray high-def, you haven't really seen the movie on home video.
Unique design, can be wall-mounted; excellent image quality on Blu-ray movies; Wi-Fi USB dongle included; Netflix and Pandora streaming; superfast operational speed and disc loading; BD-Live Profile 2.0 compatible; onboard decoding for Dolby TrueHD and DTS-HD Master Audio; 1GB onboard memory; streams media off connected PC
but: Costs more than a Sony PlayStation 3; unusual design won't fit all decors; compartment for connectivity is cramped; PC streaming setup is difficult
Also, state-of-the-art Blu-ray allows movies to be shown at their native 24 frames per second, whereas DVDs are stuck with 60 fps. The latter might seem to be better, because the number is greater. But 24-fps movies have to be compromised to get 60 displayable TV frames per second out of them, by means of a technique called "3:2 pulldown." That's geek-speak for some of the information from a given film frame being repeated in different video frames. That happens in herky-jerky fashion, such that some of the frames of the "interlaced" 60-fps TV picture wind up coming from different — frequently, mismatched — film frames. Result: a mess.
$248.70 - $299.99
BD-Live Profile 2.0-compatible; excellent video quality on most Blu-ray movies; onboard decoding for Dolby TrueHD and DTS-HD Master Audio Essential (DTS-HD Master Audio Essential differs from standard DTS-HD Master Audio in that it lacks decoding for a few legacy DTS DVD soundtrack formats such as DTS 96/24, ES, ES Matrix, and Neo:6. It still decodes all the high-resolution Blu-ray DTS soundtracks)
but: Cannot access streaming video services such as Netflix; no Wi-Fi option; no eject button on the remote; relatively slow load times; recessed USB port
So, why wouldn't you want to invest in Blu-ray?
Well, the obvious reason remains price. We would all like to see cheaper players — and they're coming. When the computer chips and the fancy blue-laser assembly that make up the guts of the player are manufactured in sufficient volume, costs will drop. The same thing happened with DVD: prices were high until chips were cheaper. (The red laser used by DVDs was already cheap, since CDs had used red lasers since the early 1980s. And, by the way, all Blu-ray players also incorporate red lasers, to play DVDs!)
DVD players got cheaper faster because (as noted above) all TV households could use them to reasonably good advantage. True, few TVs were widescreen in 1997, when DVD hit stores, but most consumers had as yet no idea their old 4:3 TVs were becoming obsolete. Today, everyone knows digital HDTVs are the state of the art. Lots of people haven't upgraded yet, but they know it's only a matter of time until they do. When and as they do, a Blu-ray player will suddenly seem mandatory for the bulk of them.
Blu-ray disc prices? They're all over the map right now. If you click here, you can check out all of the BDs sold at Amazon.com, sorted supposedly by price, low to high. (The number of results is at this moment fully 3,960, but I assume this number is inflated by some X-factor that I can't guess.) I find that Amazon's price sorting leaves something to be desired, but clearly there are numerous Blu-ray titles available for under $20.00. Many are under $15.00, and quite a few are under $10.00! An example: you can get hot titles like The Dark Knight, complete with BD-Live interactivity and an iPod-compatible "digital" version of the movie, for $23.99 instead of the $35.99 list price.
$223.00 - $311.02
Streams Netflix and YouTube; BD-Live Profile 2.0 compatible; onboard decoding for Dolby TrueHD and DTS-HD Master Audio Essential (lacks decoding for legacy DTS DVD soundtracks such as DTS 96/24, ES, ES Matrix, and Neo:6); relatively quick load times
but: Competitors offer better image quality on Blu-ray and DVD; no WiFi option
$349.00 - $399.95
Excellent image quality on Blu-ray movies; Wi-Fi USB dongle included; Netflix and Pandora streaming; superfast operational speed and disc loading; BD-Live Profile 2.0 compatible; onboard decoding for Dolby TrueHD and DTS-HD Master Audio; 7.1 analog outputs; 1GB onboard memory; streams media off connected PC
but: Costs as much as a Sony PlayStation3; front-panel controls are located on top of player; PC streaming setup is difficult
Some of the latest player models support DTS-HD Master Audio Essential, an audio codec that differs from standard DTS-HD Master Audio in that it lacks decoding for a few legacy DTS DVD soundtracks formats such as DTS 96/24, ES, ES Matrix, and Neo:6. DTS-HD Master Audio in all its lossless, 7.1-channel glory is, needless to say, still supported. This is a cost-saving measure, since it is cheaper to build a player that lacks the chips to decode the legacy formats.
On a DVD, film is transferred to video in a way that uses a different ratio of film frames to video frames. There are 30 video frames per second on a DVD, not the 24-fps rate of film. This frame-rate mismatch compromises a movie's ability to be displayed in a truly film-like fashion on a progressive-scan HDTV. DVD players do not support the 1080p24 output resolution because DVDs themselves do not.
The frame-rate mismatch makes no major difference when a DVD is played into a now-obsolete TV that uses a picture tube. But today's HDTVs don't use picture tubes, so the frame-rate mismatch causes the displayed picture to be slightly impaired. Blu-ray players and discs avoid the mismatch problem entirely.
In order to take advantage of the 24-fps frame rate of movies recorded on Blu-ray Discs, you need:
- A Blu-ray player that supports 1080p24 output on HDMI
- An HDTV that supports 1080p24 input on HDMI
- An HDMI cable to connect the player to the HDTV
- A Blu-ray Disc containing a movie or TV show shot on film
- The right setup option(s) in the player and TV
The 30-fps method used to transfer films to DVD is used due to the fact that, in the United States, TV was originally standardized to provide 30 video frames each second, even though film uses 24 frames per second.
To avoid image flicker, in the NTSC television system that was used for decades until the recent digital television revolution, and is also used on DVDs sold in the U.S., each video frame is divided into two separate "fields" transmitted 1/60 second apart. Though they represent slightly different moments in time, the two fields of each video frame can be thought of as "interlaced" together, much as the fingers of two hands folded together are interlaced together into a single unit.
Today, the NTSC standard is being replaced in the "digital conversion." This conversion has actually been going on for several years, though today we are hearing a lot about the problems it will cause for consumers who are not ready for it when, on June 12, 2009, the plug is finally pulled on analog NTSC TV broadcasts. But all DVDs sold in the U.S. will continue to be recorded in a digital version of NTSC even after the digital conversion is done.
NTSC (which is analog video) and DVDs (on which NTSC-like video is recorded digitally) use two interlaced fields per video frame, whether the interlaced analog or digital video comes right from an NTSC video camera or is transferred to video from motion picture film. Each 1/30-sec. frame of interlaced video is made up of two fields, with each field taking 1/60 second.
Frames of NTSC or DVD video (and the two fields they are each subdivided into) are composed of numerous horizontal scan lines. These lines run across the screen from left to right, but since they are stacked on top of each other in the vertical direction to make a two-dimensional picture, they serve as a measure of the "vertical resolution" of the TV picture. In each NTSC frame there are 525 scan lines, though only 480 of them are visible on the TV screen (the others are in the so-called "vertical blanking interval" and don't show up on the screen). The vertical resolution of NTSC video (and of DVDs in the U.S.) is 480 lines.
The first field of each video frame contains that frame's even-numbered scan lines, starting at line 0 at the top of the screen: 0, 2, 4, etc. The second field contains the video frame's odd-numbered scan lines: 1, 3, 5, etc.
That is the way the original NTSC TV system's video signal, which is analog, not digital, is handled. For digital video such as is recorded on a DVD, the scan lines become pixel rows, and the blanking intervals are no longer needed, but the idea remains the same.
Thus, on a DVD sold in the U.S., there are video frames lasting 1/30 second each, with each frame containing two interlaced fields. Because the picture is recorded digitally, the scan lines are now rows of pixels: 480 pixel rows per video frame. The even-numbered pixel rows (0, 2, 4, etc.) are recorded as the first field of the video frame, while the odd-numbered pixel rows (1, 3, 5, etc.) are recorded as the other field of the same frame.
The scan lines or pixel rows of a single field of interlaced video are like an arrangement of slices of a scene viewed through a window, when the slices of the scene are separated by the partially opened slats of a venetian blind. For the second of the two fields in each video frame, the view and the slats simply exchange roles: the slats now contain picture information, while what was picture information becomes slats. This picture-slats alternation happens over and over again, with one alternation every 1/30 second.
Each field of normal, non-film-originated interlaced video records information from the video scene that occurs 1/60 second after the previous field, whether that field is in the same video frame or in the prior video frame. This delay between the two fields of a video frame (or between the first field of a new frame and the last field of the immediately prior frame) worked well with old, picture-tube based TVs, since those TVs would draw the two successive fields on the screen one after the other, at the exact same 60-fields-per-second rate at which the video camera captured them in the first place. Though the two fields were drawn on the TV screen one after another, 1/60 second apart, the fact that the glow of the phosphors on the picture tube's face decayed slowly, abetted by the "persistence of vision" of the human eye, made the two fields seem simultaneous.
When film at 24 frames per second is transferred to interlaced video at 60 fps, as for an analog NTSC broadcast or a standard digital DVD in the U.S., "2:3 pulldown" is used to match the disparate frame rates of film and video. But on a Blu-ray Disc, the same film is digitally recorded at its original 24 fps. A typical Blu-ray player today (but not the early Blu-ray player models from a few years ago when Blu-ray was first introduced) can play that recording into an up-to-date 1080p HDTV at 24 fps, using a digital HDMI connection between the Blu-ray player and the HDTV. The result is much better than even the best DVD can offer, even when the DVD is played on the same Blu-ray player and viewed on the very same TV.
With 2:3 pulldown for motion-picture film that is being transferred to video — a technique which is also called "3:2 pulldown" or "telecine" — film frames are scanned to make a new video field (not a video frame, a video field) every 1/60 second. (Find out more about telecine here; the word "telecine," by the way, is pronounced either with four syllables, or with three.)
After 2:3 pulldown, every group of five sequential video frames contains exactly three of those video frames whose fields both come from just one film frame. But two of the five video frames in a five-frame group contain fields that derive from two different film frames. These two (of every five) video frames can be called "dirty frames," since they do not come from a single, "clean" film frame.
In the illustration above, the first two of the five resulting video frames are "clean," coming entirely from film frames A and B, respectively. The fifth video frame is also "clean," since both of its fields come entirely from film frame D. But the third video frame has one field scanned from film frame B and one from film frame C, and so that video frame is "dirty." So is the fourth video frame, since it has one field from film frame C and one field from film frame D.
Film frames B and C (or C and D) may come from a single film camera shot and be only slightly different from one another — or even identical, if there is no motion in the scene. However, in a far worse case, they can cross an editing splice between two different film camera shots. If they do not cross a splice and are only slightly different, objects that are in motion from one film frame to the next film frame can develop edges that look serrated rather than smooth, when video frame 3 or video frame 4 in the illustration above is viewed on a progressive TV. If they come from different film shots and are accordingly grossly different, then when viewed on a progressive TV they can look a complete mess. They are not just "dirty," they are downright "filthy." Video frames that are "dirty," even "filthy," occur typically with 2:3 pulldown and can cause problems on progressive TV displays.
What does that name, "2:3 pulldown," actually mean? It means that the machine (called a "telecine") which scans the physical film and converts its frames into interlaced video for television transmission or DVD "pulls down" the film, using its sprocket holes, in a way that holds one frame of the film in place for 1/30 second, which is the time it takes to scan two 1/60-sec. video fields. Then it pulls the next film frame into position and holds it steady for the time it takes to scan not two but three 1/60-sec. video fields: 3/60, or 1/20, second. Then the next film frame generates two video fields, and then the next generates three fields ... and so on, and so on. That simple 2-3 alternation in the pulldown of the film in the telecine machine winds up creating a mixture or "clean" and "dirty" video frames like those in the illustration above.
Today's digital TVs are "progressive," not interlaced. They are designed to present each video frame intact, not divided into two alternating sets of interlaced scan lines. Progressive TVs can be thought of as using the scan lines in the picture all at once, 0, 1, 2, 3, etc., rather than using the even-numbered scan lines and then the odd-numbered scan lines.
The letter "p" is used to designate progressive scan. When we read that an HDTV is "1080p" (or "720p") the "p" stands for the fact that the TV uses a progressive, non-interlaced display. When we read that a certain TV or cable channel is "1080i," that means that its signal has the same 1,920-pixel by 1,080-pixel resolution as 1080p, but each video frame is transmitted as two interlaced fields, 1/60 second apart, not a progressive frame with all its scan lines used at once. (1080i is like NTSC video in that regard, in fact, except that NTSC, when digitized and recorded on DVD, is "480i" rather than 1080i. It has far fewer pixel rows/scan lines and much lower resolution.)
When video that has been recorded in interlaced fashion (first the even scan lines, then the odd) is shown on a progressive TV, it must first be "deinterlaced." For a 1080p HDTV, deinterlacing a received 1080i signal is a snap: just combine each pair of successive fields, transmitted 1/60 second apart, into a single frame, and show one frame every 1/30 second.
This results in a "1080i60" video input being displayed on the TV screen as "1080p30." The "30" designation after the "1080p" means that there are 30 progressive frames shown on screen each second, rather than 60 interlaced fields per second. Likewise, the designation "1080i60" for the input video signal means video with 60 interlaced fields per second, ostensibly intended for an interlaced display. (Sometimes these and similar designations contain an embedded slash: "1080p/30" or "1080i/60". And sometimes we see "1080p@30 Hz" or "1080i@60 Hz", indicating the screen "refresh rate" in cycles per second or Hertz.)
Typically in a 1080i60 video input stream, in each span of time that contains four film frames (4/24, or 1/6, second) there are five video frames that, after being deinterlaced, need to be flashed on a progressive HDTV's screen. The extra video frame magically appears because 2:3 pulldown is done, producing "dirty" video frames by creating two interlaced-video fields from some of the film frames and three interlaced-video fields from others. This is the same as what happens with 480i video, except it is done at an HDTV resolution.
The 2:3 pulldown cadence not only creates "dirty" frames when deinterlaced and displayed progressively, it also results in a somewhat herky-jerky rendition of the motion in the picture, called "telecine judder."
Films on Blu-ray discs avoid both "dirty" frames and telecine judder because a Blu-ray Disc is encoded at 1080p24, right on the disc. This means there are 24 full progressive-video frames recorded per second recorded on the disc, just as there are 24 film frames per second recorded on film. No 2:3 pulldown is done. (Often, by the way, the official designation "1080p24" is shortened to "24p".)
Provided that a Blu-ray player is capable of sending 1080p24 video direct to an HDTV, and provided that the TV is capable of accepting it and can put the received 1080p24 video right on screen without any sort of change being made to the picture content, there is no need for the player or TV to do 2:3 pulldown compensation (sometimes called "inverse telecine") at all. Nothing must be done to hide the serrated edges and other picture defects that are commonly associated with 2:3 pulldown's "dirty" frames, when they are used by a progressive display. Telecine judder disappears. Hence, Blu-ray Discs of a Hollywood feature film can be viewed with stunning, unprecedented fidelity to the original film.
Blu-ray players actually transmit 1080p24 video to the HDTV at 24 Hz, but the TV may use each field (say) three times in refreshing the screen at a refresh rate of 72 Hz. This can reduce visible flicker, which can fatigue the eyes. However, the actual content of the video changes at a rate of one field every 1/24 second. Since 72 Hz is a whole-number multiple of 24 Hz, there is no change to the picture content.
Some HDTVs using LCD panels now refresh the screen using a 120-Hz refresh rate, such that each frame of 1080p24 is used five times. (Likewise, each field of 1080i60 video input is deinterlaced, producing 1080p60, and then each frame of that is used twice to produce a 120-Hz refresh rate.)
Whatever the actual refresh rate, whether 72 Hz or 120 Hz, the video coming out of the Blu-ray player and being displayed on the screen is actually 1080p24. Its frames match those of the original film one-for-one.
That same film on DVD is recorded at 480i60, which means that each interlaced frame consists of two fields, each with 480 ÷ 2 = 240 rows of pixels. Each field takes 1/60 second, so the two fields of any given video frame take 1/30 second.
When 480i60 is shown on a progressive TV display, it must be deinterlaced. The simplest way is to use a "line doubler." A line doubler simply combines each pair of 480i60 fields into one whole frame and shows each whole frame twice, achieving in effect 480p60 video on the screen.
Line doublers work fine for 480i that derives from a video camera, but for 480i that derives from a film that has been subjected to 2:3 pulldown, line doublers make two of every five displayed video frames "dirty" ones. Even when these frames are not "filthy" — spanning splices between film camera shots — objects in motion tend to develop serrated edges. Fast motion results in edges with pronounced comblike "teeth." The result can be the picture artifact or defect known as visible "combing":
Combing artifacts are sometimes not-so-affectionately referred to as "jaggies." The problem shows up when line-doubler deinterlacing is done for progressive TV displays. For an interlaced display such as a CRT ("picture tube") there is no need for deinterlacing. Each field is drawn sequentially onto the phosphors of the picture tube, scan line by scan line, with each field appearing 1/60 sec. after the previous one. There is no visible combing.
With a progressive TV display, combing that results from deinterlacing can be reduced by having the TV do more sophisticated deinterlacing than a line doubler does. But it can often be eliminated entirely by a DVD player, before the TV even "sees" the video signal.
Digital 480i video on DVD can optionally be recorded using a "soft telecine" type of 2:3 pulldown. Recall that in 2:3 pulldown certain video fields are used twice, once in each of two successive video frames. "Soft telecine" is a way to use "flags" recorded on the DVD to say, in effect, "The video field you would normally expect to occur here is missing. Repeat the corresponding video field from the previous video frame instead."
A "progressive-scan DVD player" can change 480i on the disc to 480p for output to the TV (assuming the TV can accept the doubling of the rate at which the TV signal is input to it). Such a player can typically use the "soft telecine" flags, if they are present on a DVD, to eliminate "dirty" progressive frames in the deinterlaced output. The basic logic is simple: just ignore repeated fields entirely. However, the frame rate generally has to be padded out from 60 fields/30 frames per second to 60 progressive frames per second, so certain of these whole frames are repeated as necessary, instead of repeating fields as needed. This eliminates combing/jaggies, but it can result in a noticeable judder on screen.
There is one further problem with 2:3 pulldown on DVD. Some DVDs use a "hard telecine" instead of flags to accomplish 2:3 pulldown, such that repeated fields are actually encoded twice, and few DVD players are able to remove it. Likewise, many "soft telecine" DVDs are poorly encoded: the flags that tell when to repeat fields are missing or inserted in wrong places. This often happens near a chapter break, at which point even a sophisticated progressive-scan player can produce on-screen jaggies.
Blu-ray players, when they are used to play DVDs, have exactly the same problems with jaggies and judder as DVD player do. But when they are used to play Blu-Ray Discs made from movies or TV shows shot on film, playback is stunningly smooth and artifact free.