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DVD Authors: Crash Your Machines!

Jun 8, 2006 8:00 AM, By Barry Baverman

I teach a regular five-day Apple DVD Studio Pro course, during which one of my goals for each student is to crash his machine. This may seem like a radical notion to some folks, especially software marketers, but I assure you there is no better way to learn DVD. This is because after addressing the basics of the interface and workflow on day one, I focus almost exclusively on command programming (scripting) and the author’s imperative to understand the GPRMs and SPRMs, which guide the DVD player and the quality of the viewer experience.

Let me explain.

GPRMs or general parameter register memory(s) are all-purpose variables that are used to track viewer behavior and interactivity. The sixteen registers in the DVD player have no pre-assigned functions; they are all equal to zero when the disc is first inserted into the machine. The DVD author simply adopts a GPRM for the desired function, then moves a value into the register. We then refer to this value in arguments placed around the disc in order to guide the player through the various forks in the road.

In contrast, SPRMs, or system parameter register memory(s), have specific assigned tasks according to the DVD specification. SPRM 0 for example defines the player and viewer’s language preference. SPRM 8 indicates the menu button highlight. SPRM 14 specifies the wide-screen preference of the viewer, that is how he wishes to screen 16x9 material, as letterbox, 4:3 pan and scan, or 16x9. As DVD authors, we can’t change system parameters such as a viewer’s language preference or parental rating (SPRM 13) without invading his home and tearing into the player’s setup menu. Of the 24 SPRMs in DVD land, nine are read-only, twelve are read/write, and three are unassigned.

Contrary to the proclamations of some industry "gurus" who, in their own interest only, seek to obfuscate the scripting process, there is nothing inherently mystical or difficult about working with GPRMs and SPRMs. DVD players are by design simple devices, so it makes sense that whatever programming is possible in the authoring environment, the number of commands available at any one moment is relatively few.

The schizoid nature of Apple DVD Studio Pro becomes apparent when one compares the spate of competing authoring tools currently crowding the market. These programs targeting consumers (and advanced consumers) often trumpet their lack of features and idiot-proof workflow, thus offering little or no direct control over the SPRMs and GPRMs that DVD professionals must urgently monitor and scrupulously track.

DVD Studio Pro, however, is another kettle of bits. As a prosumer tool, it features a substantial abstraction layer built around an attractive UI with extensive pull-down menus. The point, of course, is to reduce the apparent complexity (albeit not the actual capacity) of the authoring process. Certain routine scripting chores, such as smart button highlights, are ostensibly built into the interface, usurping one or more of the GPRMs in the abstraction layer to accomplish it. You don’t have to be aware of any of this; the details are handled for you behind the scenes, as the button you designate in the pull-down menu should presumably highlight after viewing a program.

For the professional DVDer, this approach to GPRMs and SPRMs is fundamentally flawed since it often doesn’t work; the most obvious case being when we return to a menu from which we could have come from two different buttons. When end-jumping or menuing out of a track, the built-in highlight feature or remote control menu setting in DVD Studio Pro is unreliable as it can only return to one button or another, and not the specific button from which we came. To achieve this functionality in a professional title, viewer interactivity must be tracked for each individual viewing, which means setting and then referencing a GPRM assigned to this purpose. To the DVD professional, those “features” that work only part of the time are not really features at all but defects waiting to be uncovered in your project’s QC report.

While DVD Studio Pro would appear to suffer from the same malady as other heavily abstracted authoring tools, there’s a difference here—and it’s a big one. The program’s scripting engine is borrowed almost completely from the highest end unabstracted authoring systems, thus enabling critical manual control of GPRMs and SPRMs. This means despite the attractive easy-to-use interface, the DVD Studio Pro professional author has direct access to eight of the 16 GPRMs (0 through 7) in the player.

This is where the crashing part comes in. As DVD Studio Pro users, we professionals face a choice in how we want to live our lives. We can blindly follow the abstraction layer’s dictates and limitations (such as ill-tracking of button highlights) and bear the consequences, or we can blaze our own path and take control of our craft like real DVD authors. The latter scenario just possibly precipitating a crash by sending dual, and potentially conflicting, commands to the simulator and/or application.

This begs a serious issue for professional users whose direct control of GPRMSs and SPRMs may be at odds with the abstract commands that may be working unknowingly behind the scenes. For the pro author in DVD Studio Pro, the issue becomes, at any given moment, just which side of the program’s abstraction layer are we really on?

To its credit, DVD Studio Pro is unique in allowing a high-level of authoring prowess in a mid-range tool. (Owing to this crash business, there’s a reason why there is no PC-based equivalent!) But all of this ability to control GPRMs and SPRMs in DVD SP is also a major challenge, as my bone-weary students will often attest in discovering the limits of the program’s abstraction. Like a freeway that abruptly ends and the driver finds himself on unfamiliar side roads, navigating on the far side of the attraction layer in DVD Studio Pro requires an understanding of DVD fundamentals. Menu buttons referred to in the abstract by a simple button number must be shifted manually (in SPRM 8) from bit one to bit 10 when driving on the side roads. This means at some point in his journey, the pro-level author will leave the abstraction freeway, and must utilize values directly relatable by the player, which in the case of button “1” means referencing a value of 1024 in the scripting.

The potential conflict of not knowing which side of the abstraction layer one is on sets up a potential crash scenario inside DVD Studio Pro that is unique in the authoring trenches. Disconcerting perhaps to software developers, a crash can be nonetheless highly empowering to the DVD professional. Like any craftsman, the true DVDer understands the limits of his tools and how hard he can lean on them until the bit breaks or an overtaxed motor burns out. When DVD Studio Pro quits on day four of my class and I hear the exasperated frustrated cries of my students, I feel elated. I’ve done my job well.

© 2008 Penton Media, Inc.