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Simple DVD Spec. Re-Authoring With DVDAfterEdit, Part 2

By Ben Weinrach

Welcome to Part 2! Although the content is very similar, the layout of this project is very different from that of the 4 track project in Part 1, mainly, we're adding a scene selection menu, which will require a little more programming. I'll show you how to use 2 GPRM's and a decent variety of Pre- and Post-Commands to get this project working properly, and also discuss some DVD player default behavior governed by the DVD Specification. Spec. authoring gives the author more choices of how to organize and program a disc, and what is presented here is only one of several possibilities.

One quick note: this article refers to basic operations, terminology, and techniques found in Simple DVD Spec. Re-Authoring With DVDAfterEdit 2, Part 1. My intention is to focus on the new stuff, so please review Part 1 for more detail on certain subjects like 'Title' and 'Menu' remote key assignments, for example.

The '4 Chapter' project contains a 15 frame/1 GOP First Play in VTS 2, a track with 4 chapters in VTS 1, the Main Menu in the VMG, and the Scene Selection Menu in VTSM 1. There are no dummy menus (with one inconsequential exception), but there are a lot more commands. Unlike most Hollywood DVD's I've seen, navigation originating from the Scene Selection Menu on this disc returns there, even if the “Menu” remote key is activated. Activation of the 'Title' remote key always returns navigation to the Main Menu with the proper button highlighted.

I chose to put the Main Menu in the VMG as it is the top-most menu in this disc's structure, while the Scene Selection Menu remains in VTS 1. Placing menus in the VMG can make programming easier and speed-up navigation as projects grow in size and complexity. Although the Scene Selection Menu could also reside in the VMG, this example will show some techniques for moving navigation between the VMG, VTSM, and VTS domains.

The file called '4CHAP.zip' contains the before and after DVDAfterEdit builds, and can be found in the member download area.

Adjusting The Layout

Here's the left pane of the DVDSP 3 build:

The first thing we need to do is move the Main Menu in VTSM 1 PGC 7 to the VMG. Select 'VMG Menus' in the left pane, and then in the File menu select the 'Replace Menu Vob…' command.

Choose VTS_01_0.VOB in the 4CHAP_ORIGINAL VIDEO_TS folder. VTSM menus are always located in the VTS_XX_0.VOB file, and DVD Studio Pro 3 always places 4:3 menus in VTS 1. The 'Import Commands With VOB' option doesn't affect this project, since we'll be deleting them anyway. A progress bar will appear at the top of the right pane. This will finish quickly due to the size of the VOB being imported.

The VMG Menus should now be displayed like this in the left pane:

Let's delete the dummy PGC's we don't need - which is almost all of them! Delete every PGC in the VMG except VMG PGC 7 (Main Menu). Notice how VMG PGC 7 has been automatically changed to VMG PGC 1. Then set its 'entry PGC' parameter to 'yes' so this PGC becomes the target for the 'Title' remote key. As a quick reminder, I've included the two pictures below from the “4 Track” project discussed in Part 1. Please review the articlefor more information regarding these assignments.

Next, delete every PGC in VTSM 1 except for VTSM 1 PGC 8 - this is the Scene Selection Menu. Be sure to change its 'entry PGC' and 'Menu Type' parameters to 'yes' and 'root,' respectively, so this PGC becomes the target for the 'Menu' remote key.

Now delete all of the PGC's in VTSM 2. This remaining PGC is where our only dummy menu resides. This dummy PGC doesn't really serve any purpose for this disc because VTS 2 is the target of the First Play and has all user operations disabled. It will never call or navigate to its VTS menu.

Finally, delete all commands in the project with my favorite DVDAfterEdit 3 command, 'Delete All Commands In Project.' The left pane should now look like this:

GPRM Definitions

Now that the project's layout is set, it's time to dive into the fun stuff. I'm using only 2 GPRM's for this disc and their definitions follow below. I'll go into greater detail when we look at the programming for each area of the disc.

r0 = Menu Status

This GPRM is used to keep track of which menu navigation is going to and coming from. It keeps track of from where VTS 1 was activated - whether from the Main Menu or the Scene Selection Menu. It also handles what happens when the Title and Menu remote keys are activated, so navigation gets directed to the correct location. It also assists with how button highlights are determined for the Main Menu. This will be clearer in just a bit.

r1 = Scene Selection Menu button highlight

This GPRM is used to define which button will be highlighted while on the Scene Selection Menu. More detail to come...

All Commands Revealed!

The picture below shows all of the PGC's in this project and their respective commands. Feel free to insert all of these commands at any time. Details about their functions follow, PGC by PGC.

First Play

I use the First Play Pre-Command area to set up all of the values needed to start the disc. This can also be accomplished in various Pre- or Post-Command areas prior to the Main Menu, depending on the project. Here are the Pre-Commands:

GPRM 0 is set to a value of 0, and then navigation to jumps to VTS 2. Notice that the 'Set' command set is being used. If you click on the command pull-down menu, you'll see several 'Set' commands, including 'Set GPRM.' Although we are setting a GPRM, the generic 'Set' is more versatile, allowing us to set several things, including values from SPRM's - which we'll do shortly. Also - in this instance - it has a cleaner look. If 'Set GPRM' were used, the First Play Pre-Commands would look like this:

VTS 2: 15 Frames/1 GOP

Since navigation arrives here after the First Play, we may as well follow it. I make it a habit to start my discs with a track, and if there isn't any content that needs to display before the main menu, I use this - a VTS with 15 frames (1 GOP) of video and audio.

The only command in this PGC is a Post-Command that 'calls' VMG PGC 1, which directs navigation to the Main Menu.

VTSM 2: Dummy PGC

Might as well get this out of the way - again (just being thorough...). To recap., this PGC serves no purpose except to exist - though technically I don't think it even needs to do that. As of now, we cannot delete the VTSM without deleting the entire respective VTS - which we don't want to do. So 'just in case,' I've inserted the 'Jump VMG PGC 1' command. Before we move onto the bulk of the commands in this project, let's take a look at VTS 1.

VTS 1: Track w/4 Chapters

VTS 1 is the main 'show' on this disc, and has 4 chapters. These chapters are accessed from the Scene Selection Menu by using Jump VTS_PTT as a button command. VTS 1 has the following Post-Commands, but no Pre-Commands:

Line 1: If GPRM 0 is equal to a value of 1, then navigation goes to line 3, skipping the command in line 2.

Line 2: So if GPRM 0 is not equal to a value of 1, then navigation “Calls” (or jumps) to the Main Menu, which is VMG PGC 1.

Line 3: This line instructs navigation to jump to the VTSM of VTS 1, which is the Scene Selection Menu.

Setting up VTS 1 like this prevents any unnecessary domain and/or PGC jumping. Wherever navigation originated to get to this VTS, it immediately returns. Of course Pre-Commands could be inserted depending on what is required by the disc. But keep in mind that when a PTT (chapter) in a VTS (show) is being directly accessed via the Jump VTS_PTT command, navigation visits the Pre-Command area of the PGC before jumping to the chapter - so any commands there will execute. In fact, a lot of things happen before navigation gets to the chapter via Jump VTS_PTT, according to the DVD Specification:

1) Stop the current presentation.

2) Discard the RSM [Resume] Info (if it exists), Assign '0' to SPRM 9 to stop the Nav timer.

3) Set SPRM 1 and SPRM 2 [Audio Stream & Subpicture Stream]

4) Execute the command in the Pre-Command Area of the PGC in which the PTTN [Part of Title Number] is found.

5) Start the presentation of the PTT [Part of Title a.k.a. chapter], which is specified by the PTTN and VTS_TTN [Video Title Set Title Number] within the current VTS-space.

So in order for this disc to operate correctly as programmed, no Pre-Commands have been inserted in VTS 1.

VMG: Main Menu

Here are the Pre-Commands for the VMG:

Isolated in this way, these Pre-Commands may be a little tricky to understand since they work in relation to other commands in the project. I'll review them line by line, and you may find it helpful to look at the picture above that shows all of the commands in the project.

Line 1: If GPRM 0 is equal to a value of 0, then go to line 4. Remember that GPRM 0 is used to keep track of menu-related navigation. At the First Play, since GPRM 0 is set to the value of 0, navigation moves to line 4 - skipping the commands in lines 2 and 3 the first time through.

Line 2: So if GPRM 0 is not equal to a value of 0, navigation forces a value of 2048 into SPRM 8, in order to highlight button number 2.

Line 3: Once the button is set, navigation skips to line 5.

Line 4: This command sticks a value of 1024 into SPRM 8 in order to have button number 1 highlighted.

Line 5: GPRM 0 gets reset back to a value of 0, since navigation has arrived (and will currently stay) at the Main Menu. If navigation originated from the Main Menu (or the First Play), this value is already set to 0 - so nothing changes.

The 'GoTo Line' commands set up a bunch of conditions, and are configured in such a way as to control exactly what happens when navigation enters the Main Menu. So for example, if the disc is started and the show is activated by button 1 on the Main Menu, GPRM 0 will stay equal to 0. When the show is finished playing, navigation will first execute the Post-Commands in VTS 1. If navigation is directed back to the VMG/Main Menu, it checks the first line, skips to line 4, sets button 1 to highlight, and finally resets GPRM 0 to 0 (which it already is). This may seem like quite a few steps just to get button 1 to highlight, but how many steps do abstraction layer authoring applications use? They send navigation all over the place, jumping from PGC to PGC and line after line of commands, slowing the responsiveness of the DVD. These Pre-Commands also function correctly if the Title and Menu remote keys are activated. Since the Title remote key is hard wired to VMG PGC 1, whenever it's activated navigation comes here first. If you look at the disc's layout picture above, there are Pre-Commands in VTSM 1 – which VTS 1's Menu remote key is hard wired to – that will redirect navigation to the Main Menu if that is where it originated. For more detail on how this works, please see Part 1.

The Button Commands are simple enough:

Button 1's instruction jumps navigation to VTS 1, which has no Pre-Commands. Button 2's Link TailPGC instruction jumps navigation to the Post-Command area of VMG PGC 1 - the current PGC. Since a button can generally only have a single command, this is a great alternative to jumping to a dummy menu if more instructions are required. In this case, we need to change a GPRM value and set a button (force a new value into SPRM 8) before we jump to the Scene Selection Menu, our final target. The Link TailPGC command is part of the Link Sub-Ins (Link Sub-Instruction) command set. “Link” commands are often used to move navigation within a PGC, like to a different Cell. A common example is the use of Link TopC (Link Top Cell) to loop a motion menu.

Here are the Post-Commands for the VMG PGC 1, which in this project are only accessed from button 2 of the Main Menu:

GPRM 0 gets changed to a value of 1, the button number gets set to 1, and navigation leaves the Main Menu and jumps to VTSM 1, the Scene Selection Menu. I'm using the 'Set Button' command to force the value of SPRM 8 to 1024, because the first time navigation arrives at the Scene Selection Menu, button 1 should be highlighted. If this command is not used, then button 2 will be highlighted because the last selected/activated button was button 2 on the Main Menu, which would make the value of SPRM 8 equal 2048. Later I will go into some detail concerning some DVD Specification rules that govern how DVD players determine which button to highlight in certain situations.

VTSM 1/Scene Selection Menu

These are the Pre-Commands for VTSM 1:

Line 1: If GPRM 0 is equal to a value of 1, navigation skips to line 3. There is only one instance when navigation would not skip to line 3, but move down to line 2. Pop quiz: do you know when this would happen?

Answer: if VTS 1 was activated from the Main Menu (GPRM 0 0) and the menu remote key was activated during the show. If you are not clear on why this is, check Part 1 of this article series! : )

Line 2: Navigation not skipping to line 3 gets sent to the Main Menu.

Line 3: This command assigns the value of SPRM 8 to GPRM 1.

Line 4: The value in GPRM 1 assigns the button highlight.

Before I explain what is happening here, let's take a quick look at the Button Commands:

Buttons 1 - 4 jump to their respective PTT's (Parts of Title - or chapters). Button 5 sends navigation to the Main Menu.

In order to get the correct button to highlight upon arrival (or return) to the Scene Selection Menu, I'm using GPRM 1 to set the button highlight from the value in SPRM 8. When navigation gets sent to the Scene Selection Menu from the Main Menu, button 1 is highlighted because a value of 1024 was forced into SPRM 8 upon leaving the Main Menu.

If chapter 3 is played by the activation of button 3, 3072 is immediately stored in SPRM 8. When the show finishes (or the menu remote key is activated) and navigation returns, the commands instruct GPRM 1 to grab the value of SPRM 8, and set the button highlight accordingly.

No VTSM 1 Post-Commands are necessary for this example project.

Do We Really Need All Of These Commands?

The majority of commands in this project are used to 1) highlight the desired button, and 2) select the menu that the button was activated from in the first place - no matter the cause (end of show, Title or Menu remote key activation, etc.). The DVD Specification has a few default rules DVD players are supposed to follow that apply when there is no forced button selection:

a) When Force Select Button is set, the value of Force Select Button is assigned to SPRM (8).

b) When Force Select Button is not set,

b-1) If the current value of SPRM (8) is equal to or less than the number of Buttons during the period, SPRM (8) is unchanged.

b-2) If the current value of SPRM (8) is greater than the number of Buttons during the period, the value of SPRM (8) is set to the largest BTNN.

Force Select Button is usually assigned in the authoring application. DVD Studio Pro 3 refers to this as 'Default Button.' The parameter can also be assigned with DVDAfterEdit, and can be found on the 2nd to last line of 'Button Highlights' in the Nav packs.

The 4 Chapter project does not use any Force Select Buttons - the button highlights are assigned throughout the various Pre- & Post-Commands. To see how these rules work, first take a look at this modified version of the 4 Chapter disc:

Notice how nearly all of the commands to control button highlights have been removed, with only three exceptions. A 'Set Button 1' Pre-Command has been added to the First Play so the correct button highlights when the DVD starts (just for safety), a 'Set Button 2' command remains in the VMG Pre-Command area, as well as a “Set Button 1” command in the VMG Post-Command area. Otherwise, the Pre-Commands are only used to direct navigation when the show finishes playing, or if the Title or Menu remote keys are activated. This version of the 4 Chapter project will behave just like the more elaborate previous version in DVDAfterEdit's 3's Tracer function, and in theory, all DVD players. Let's apply the above DVD Specification rules - here they are again:

a) When Force Select Button is set, the value of Force Select Button is assigned to SPRM (8).

b) When Force Select Button is not set,

b-1) If the current value of SPRM (8) is equal to or less than the number of Buttons during the period, SPRM (8) is unchanged.

b-2) If the current value of SPRM (8) is greater than the number of Buttons during the period, the value of SPRM (8) is set to the largest BTNN.

a) Doesn't apply. SPRM 8 keeps track of that last selected/activated button, and a Force Select Button replaces whatever value was previously in that register. Though this project does have three instances of a 'Set Button' Command forcing the value of SPRM 8 to change, navigation always determines which button should be highlighted, not the Force Select Button parameters. If the Force Select Button parameters were set, the highlighted button number would never change for a given menu.

One quick thing - the first two VMG Pre-Commands are only there to ensure that button 2 is highlighted if the Title remote key is activated when navigation originates from the Scene Selection Menu. If they are removed that functionality is lost, but the Force Select Button rules will highlight the correct button automatically for all other situations. Here's how it works:

b-1) To play the show from the Main Menu, button 1 needs to be activated. When this happens, a value of 1024 is immediately stored in SPRM 8. When the show finishes playing, navigation returns to the Main Menu, and sees that it has two buttons. Since the number of buttons hasn't changed, SPRM 8 is unaffected, and the DVD player highlights button 1 by referencing the value of SPRM 8.

To navigate to the Scene Selection Menu, button 2 on the Main Menu needs to be activated. When this happens, a value of 2048 is immedately stored on SPRM 8. Before navigation leaves the Main menu, however, it's instructed to change SPRM 8 to 1024, because button 1 should be highlighted upon arrival. What happens if the value of SPRM 8 isn't changed? Button 2 would be highlighted on the Scene Selection Menu upon arrival, because the DVD player would find a value of 2048 in SPRM 8. Since the Main Menu has only two buttons as compared to the five buttons on the Scene Selection Menu, the value of SPRM 8 will always be less than the maximum value of SPRM 8 that the Scene Selection Menu can accommodate (5120 is the value for button #5). So in this instance, SPRM 8 will not be affected (remember, by player default), according to rule b-1, because the Main Menu's maximum SPRM 8 value is only 2048.

Another example of how b-1 works would be if button 4 (Chapter 4) were activated on the Scene Selection Menu. Navigation would play chapter 4 then return. Since the number of buttons hasn't changed, SPRM 8 would not be affected, and button 4 would be highlighted. Now, rule b-2...

b-2) To navigate from the Scene Selection Menu to the Main Menu, button 5 needs to be activated - which will make the value of SPRM 8, 5120. When navigation reaches the Main menu, 5120 cannot be directly accommodated, as there are only two buttons. According to rule b-2, the highest button number will be highlighted - in this case button 2.

So, are all these commands that control the highlighted button numbers really necessary? Just a little while ago, I mentioned that this modified 4 Chapter disc will behave in DVD players the same way as the slightly more elaborate version - in theory. The truth is, not all DVD players are created equal - hence the ongoing issue that even replicated DVD's that are supposedly 110% perfect may not be compatible with every DVD player ever made - let alone all of the other DVD's floating around out there. For the sake of compatibility, and the fact that as DVD authors, we need to control how a disc functions as opposed to the player, these commands are... well... recommended. They don't allow the DVD player to make any decisions - it will just follow instructions - something players usually do well. As long as the instructions are good, everything should work as expected.... in theory!

I hope you have found these first two articles helpful, and I hope they inspire you to spec. re-author your discs. The more I re-author in DVDAfterEdit, the more necessary I believe it is. Just recently, a client of mine even noticed the difference. I updated his DVD with some new content, and then re-authored the project, eliminating all of the 'obstruction layer' commands and PGC's. He commented that the disc is much more responsive than before, even in his old PowerBook - which often has problems with all kinds of DVD's.