What's The Difference Between BD-Rs And Regular Blu-Rays?

by Justin Sevakis,

Anonymous asks:

So one thing I've been wondering about is what exactly is the difference between a BD-R and a regular BD for Blu-Ray Discs? I've been wondering since I recently went on a search for them, but all I can find is BD-R or BD-RE etc, yet companies at least from what I understand just use "BDs". How is it companies make plain "BDs" themselves exactly and what are they?

The difference between a professionally pressed, or "replicated" disc, and a recordable disc is a pretty major one. That's true of all of the major disc formats, from CD/CD-R to Blu-ray.

Mass producing "real" discs is not something any of the publishers do themselves -- not the anime companies, and not even the major Hollywood studios. Replication is a highly specialized process that requires millions of dollars worth of equipment, a clean room, and several highly paid engineers. As such, it must be done at a specialized factory, such as Sony DADC, CD Video Manufacturing, Cinram Group, or several others. DVD replication is done by a ton of companies, while Blu-ray is mostly handled by just a few, and the others just pretend to do them while really sending the work to these guys. (Full disclosure: my company MediaOCD has a business relationship with CD Video)

To make a disc, a special master set of files (called a DDP for CD and DVD, and BDCMF for Blu-ray) is sent to the mastering plant. After running a battery of tests of the files, encryption is applied, and the data from those files is etched onto a special "glass master" in a clean room. That glass master is then loaded into a stamper, and used to stamp out perfect copies onto discs. The discs are then coated in a reflective substance, sandwiched, and bound together.

CDs, and later DVDs and Blu-rays, all work according to the same principle: the data is a series of pits that are etched onto the disc in a spiral pattern, starting from the center of the disc and winding outward. When a disc is played back, the laser reads the pattern of pits, and translates that into a digital signal. CD had "tracks" separating each song physically, a bit like a vinyl record, but DVD and Blu-ray have a full computer file system to keep track of what's on those discs. DVD and Blu-ray also have dual-layer discs, which actually have two layers of data, and in order to read the inner layer, a player must re-focus its laser and pass through the outer layer.

When CD-Rs were invented (many years after the CD was introduced), the metal layer was replaced with a special dye that changed color when hit by a laser at a higher-than-normal intensity. What's etched onto the blank disc is basically just an empty groove, along with some additional data about the disc itself. When the disc gets burned, the optical drive turns up the intensity of the laser and etches a pattern of pits onto the dye layer. Then, when it gets played back, a laser reads those pits just as if it were etched onto the plastic itself.

DVD-Rs and BD-Rs are great, but they have some pretty significant limitations. They take forever to burn, they're not that reliable (especially dual layer discs), and can't support copy protection such as CSS or AACS, which are built into the DVD and Blu-ray specifications. While CSS and AACS can be broken, they do stop a lot of casual copying, and are required to be used, according to the terms of most license agreements.

Mass-produced discs are far, far more reliable than burned discs. They reflect more light, and they don't have any of the flaws inherent in a recording that came from a cheap consumer laser and motor -- both of which are subject to minor variations in AC voltage, dust, hard drive activity on the computer they're attached to, and whatever else. The recordings made by a burner are always full of errors that must be corrected later, when the player reads them.

For single layered discs this is no big deal, but dual layer discs are so difficult to burn reliably that even at the slowest burn speeds, many recordings end up not working well. The reflective surface, burdened with two layers of photosensitive dye, can't reflect very much light, so many players struggle to read these discs. In fact, compatibility is so bad that most professionals don't even use dual layer recordables for anything but internal testing. Dual layer BD-Rs were also quite expensive until recently, and are still nearly US$2 apiece.

Mass-produced discs last much longer, too. The chemical element inside of a recordable disc will often "go bad" over time -- maybe 10 or 20 years, depending on how its cared for -- and give way to chemical reaction, resulting in an unreadable disc. A well-made replicated disc is predicted to stay readable in excess of 100 years (possibly more -- we don't know yet!).

There are automated duplicators, that are basically specialized boxes with lots of BD-R drives that will automatically copy a disc to any number of recordable blanks. In fact, some companies even offer duplication services, together with custom color disc label and jacket printing, assembly, and shrink wrap. However, this is very slow and labor intensive, and if you're making more than a few hundred copies, going to a replication plant and getting your disc properly replicated is going to be cheaper, easier, and faster.

If you collect discs, a DVD-R or BD-R is better than nothing. But they will always be far less desirable than a properly mass-produced recording.

Got questions for me? Send them in! The e-mail address, as always, is answerman (at!)

Justin Sevakis is the founder of Anime News Network, and owner of the video production company MediaOCD. You can follow him on Twitter at @worldofcrap.

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