Brand-new and appetizingly shrink-wrapped — the long-awaited Blu-ray release of your favorite movie stands before you on the store’s shelves. Grab your copy, pay for it, take it home — and enjoy top-quality video and audio in your living room. But what goes into making a Blu-ray disc? Are they complicated to manufacture? We travelled to the Czech capital, Prague, and the German town of Gütersloh to watch the making of the “Iron Man” Blu-ray disc.

A Hollywood blockbuster isn’t made overnight. Even once filming is long since finished and the movie has already been released in movie theaters, work continues on the Blu-ray release. This involves a great deal of effort and, and you’ll see, can often take several months to complete.

But we’re not just talking about some low-budget movie, lovelessly slapped onto a disc, with a mediocre picture and no extra features. We’re talking about one of the most spectacular comic-book movie adaptations of all time, “Iron Man”! The Blu-ray release also gleams, not only with a stunning picture and brutally powerful sound, but also with loads of bonus features — check out our Iron Man Blu-ray review for more detailed information on these.

So it’s no wonder, really, that it takes so much work to produce a Blu-ray. Blu-ray is said to be the medium of the future and is currently trying hard to conquer the mass market. And that’s no easy task — Blu-rays are significantly pricier, more complicated, and more error-prone than DVD productions, but also, ultimately, much more fun to watch!

Lights off, curtain up — and action!

Prague: the city of a hundred spires.

Prague, late summer, 2008: We’re visiting the company Digital Media Production (DMP), where German distributor Concorde is having another of its discs authored. And yes, authoring is as complicated as it sounds. We find some members of staff working on several screens at once, some with up to ten (!) Blu-ray players standing on their desks. But let’s take this one step at a time: Authoring is a collective term for various stages of production, such as audio and video encoding, menu design, and development of BD-Live content.

We meet Annika Černá, who’s been weaving together the various threads of the authoring process since March 2008. As Head Coordinator, she organizes and supervises all of the people that take part in the authoring process: graphic designers, programmers, encoding technicians, quality controllers. “Iron Man was our most time-consuming Blu-ray project so far”, says Černá.

Annika Černá is DMP’s Head Coordinator for DVD and Blu-ray.

The especially demanding aspects, Černá tells us, were the encoding and the preparation and verification of materials. Preparing the audio streams also turned out to be time-consuming. At the start of every production, they set out a kind of budget. They can only produce this when they know exactly what has to go on the disc. Then, explains Černá, DMP allocates bit rates for the video and audio streams, as well as for the bonus materials. The chosen bit rates determine the required storage space. A maximum of 50 gigabytes is possible, but “Iron Man”, with all of its trimmings, uses only 43 gigabytes.

So why leave empty space? This is because some of the bonus materials were delivered very late from the USA, and it wasn’t therefore clear how long the individual pieces would be. To avoid falling foul of uncertainty, the authoring team were generous when calculating the “bit budget” — that is, they left a safety zone, so to speak. But, according to Černá, this doesn’t mean they’ve had to reduce the quality of the movie itself; she explains that using the highest possible bit rate doesn’t necessarily give the best picture quality: “With encoding, you can often achieve an optimum result with a lower bit rate than the maximum permitted value. Above a certain bit rate, which varies depending on the picture, there’s no visible improvement in quality.”

So what are the final figures for “Iron Man”? On average, the DTS-HD tracks have a bit rate of around 3 Mbit/s, the movie 18 Mbit/s, and the HD extras 17 to 18 Mbit/s.

So, what next? Encoding!

Video encoding with the latest software.

As soon as they’ve determined the basic structure of a Blu-ray, the DMP technicians begin work on the video encoding. This process involves taking the movie from the HDCAM SR tapes and transferring it onto two different SCSI RAID hard-disk systems. One is then used for authoring, the other exclusively for encoding — this is so that the two teams don’t get in each other’s way. If, for example, a graphic designer was to access the movie during the encoding, this would halt the encoding process.

As with all Blu-rays from Concorde, “Iron Man” also uses the VC1 codec. Thanks to a ‘rendering farm’ consisting of nine dual-core PCs (with 3.2-GHz Intel Xeon processors), the software-based encoding of a movie takes 11 hours on average. This is generally takes place overnight.

The ‘rendering farm’ at DMP: Video encoding for a movie takes 11 hours on average.

The process is significantly faster for the sound: For “Iron Man”, DMP received master tapes containing the soundtrack in WAV format at the original movie-theater speed — that is, adjusted to a frame rate of 23.98 frames per second. Since, however, Blu-ray stores precisely 24 frames per second, the sound requires slight correction using special software.

Audio encoding at DMP in Prague.

The software used — DTS Master Audio Suite — takes just half an hour to encode the movie’s soundtrack into DTS-HD Master Audio 5.1 format at 48 kilohertz and 16 bits. It’s not a question of space that limits the audio to 16 instead of 24 bits; rather, 16 bits is simply the quality of the supplied master tapes. So, this all sounds easy enough — but the big job still lies ahead: audiovisual quality control.

Quality control:

Miroslav Kozel carrying out quality control. In the background you can see his mountain of Blu-ray players.

Different scene, same building, just a few rooms down the hall: audiovisual quality control. We’re flabbergasted to discover a ten-unit-high stack of Blu-ray players at Miroslav Kozel’s workstation. Why so many? Kozel explains that quality control involves testing the movie on all players currently on the market. We can’t help but wonder what they’ll do in a few years time, when the number of players has doubled or tripled…

But back to the testing: at various viewing stations, technicians analyze the video and audio, looking for errors such as digital artifacts, audio dropouts, or clipping — and, of course, they watch and listen to the movie several times to make sure. If errors become apparent, they’re corrected via manual encoding. The technicians also check if the subtitles appear at the correct points in the movie.

Menus and graphics:
Along with carrying out the encoding, the Prague team also develops the menu structure, which has been planned in advance with Concorde and other companies involved in the production. They decided early on to use BD-Java and not HDMV as the authoring mode (see box below).

The first step is to watch the movie, so that they can select the best images for the chapter-selection screen. The menu graphics are designed in Photoshop, then the graphic designer forwards his designs to the BD-Java programmer, who turns the images into fluid animations. For example, the menu buttons should light up as the cursor moves past them. This will only work, however, if the programmer receives functional designs.

Unlike with DVDs, therefore, Blu-ray graphic designers need to understand complex aspects of programming in BD-Java. Finally, all the menus are checked again to ensure that they run smoothly — it’s a time-consuming job, but one that has to be done.

Bonus features and BD-Live:

The “Kaleidoscope” software is used to produce BD-Java menus.

“Iron Man” was the first Concorde release ever to feature a BD-Live link-up. For this, DMP didn’t resort to using outside programmers; instead, the company developed a BD-Live application itself, having first obtained a special BD-Live license from the Blu-ray Disc Association.