Menu preview cells

[VRYK]

While I can see the utility of preview cells for moving menus, what purpose do they play in still menus? I notice that PgcEdit in Trace Mode has the option to “Blank this Cell”. I have 3 such preview cells (for Audio, Chapter and Extra menus) in the VMGM domain, with the “final” menus in the VTSM domain. While I though that jumps from the VMGM can only be to a VTSM Root Menu, the jump between the Audio preview and final menus is direct and functions OK.

[r0lZ]

While I can see the utility of preview cells for moving menus, what purpose do they play in still menus? I notice that PgcEdit in Trace Mode has the option to “Blank this Cell”.

Right. It's the first reason. Another reason is that many users want to see exactly what cells are played and when.

I have 3 such preview cells (for Audio, Chapter and Extra menus) in the VMGM domain, with the “final” menus in the VTSM domain. While I though that jumps from the VMGM can only be to a VTSM Root Menu, the jump between the Audio preview and final menus is direct and functions OK.

No, you can only jump from the VMGM to a VTSM entry menu PGC. Entry menus are all menus labelled with RootM, AudioM, SubpicM, ChapterM and AngleM. The other PGCs of the VTSM (without *M label) cannot be accessed directly from the VMGM.

Not sure what you call "final menu". Since it is in the VMGM, I suppose it's the TitleM. It's also an entry menu, but unlike the VTSM, it is always possible to jump to any PGC in the VMGM, even to a non-entry menu, without *M label (with Jump/CallSS_VMGM_PGC).

Don't ask me why they decided to not implement the Jump to any VTSM PGC. It was perfectly possible to implement the command JumpSS_VTSM_PGC, but it is not present. It's one of the stupid decisions of the authors of the DVD-Video specs.

[VRYK]

>Not sure what you call "final menu".<
Sorry, I meant to say final Cell (i.e. the one linked to the preview cell).

The 3 jumps from preview cells are not from the VMGM TitleM but from other VMGM PGCs. The jump to an AudioM (which covers both audio and subtitles) is fine, but that to a labelled ChapterM is marked “TTN <ILLEGAL VALUE 0>”. Both VTSM1-3 (labelled) and VTSM1-4 hold chapter menus. Is it the fact that there are in fact 2 chapter menus which are causing the problem?
The third jump is to the VTSM2 RootM whose pre-commands include a link to PGC2 which holds the Extras menu. However, the RootM is a dummy and the jump from the VMGM has the same error message as for the ChapterM jump.

[r0lZ]

Well, in fact, the author can put the menus in any PGC (including in VTST PGCs!)
Also, a menu can be made of several cells in the same PGC or of several different PGCs. Usually, the chapter menu has several cells, and it can therefore be in several PGCs.

The VTSM menus with labels are special in two ways:

1. As explained above, they are "entry menus" and they can be targets for jumps from the VMGM.

2. If you press the corresponding button on the remote, the menu is called automatically (unless a PUO prohibits that operation). For example, when you press the "Root Menu" button on the remote (usually simply called "Menu"), the RootM PGC of the current VTS is called. That doesn't mean that the RootM PGC must contain a menu with buttons. It can even be a dummy, with jumps or links to other PGCs, containing the real menu.
Similarly, pressing the "Top Menu" button jumps to the TitleM PGC of the VMGM.

Note also that most remote do not have specific buttons to call the Subpic, Audio, Angle or Chapter menus. It's only a limitation of the hardware, but theoretically it is possible to implement these buttons. However, most remotes have Subtitle, Audio, Angle or Chapter buttons, used to display the internal menu of the player. Pressing twice these buttons can sometimes emulate the real Subtitle, Audio, Angle or Chapter buttons, and jump to the corresponding entry PGC. Again, the possibilities depend of the hardware.

Anyway, to understand how the navigation of your DVD works, use the trace mode, and play with the buttons of the virtual remote. If a specific menu cannot be accessed, that might be due to an authoring bug, or be intentional.

... but that to a labelled ChapterM is marked “TTN ILLEGAL VALUE 0”.

Change it to 1. The TTN parameter is usually ignored. (It should contain normally the TTN number of the calling PGC, but it has no real usage.)

[VRYK]

Many thanks for the clarifications.
My impression that jumps from the VMGM domain were limited to the Root Menu in the VTSM domain came from your summary in Appendix 4 of the PgcEdit Manual.

Changing the TTN parameter to 1 worked fine. In fact, PgcEdit even did this automatically when I opened the editor.

[r0lZ]

Oh well, the doc has not been written by me. There might be some errors, although I did my best to verify it.

In fact, PgcEdit even did this automatically when I opened the editor.