[mythtv-users] MythArchive: Stuck in Chapter Menu

Michael T. Dean mtdean at thirdcontact.com
Thu Sep 28 22:48:47 UTC 2006

On 09/28/06 13:11, Paul Harrison wrote:

>Rachel Stanley wrote:
>>The only way I've found to get back to the main menu is to hit the "skip to 
>>the next chapter" button.  Once I get to the end of the title, it returns to 
>>the root menu.  Or you can go to the chapter menu, select the last chapter, 
>>then hit the skip to next  chapter.
>>If anyone else knows a better way (or knows how to put a main menu button on 
>>the chapter menus), I'd be thrilled.
>The two DVD players that I have access to both have "Top Menu" buttons 
>on the remote which always go back to the main menu. Similarly the 
>"Menu" button always goes to the chapter menu for the currently playing 
>title. If you use xine the default keys are "F1" to go to the main menu 
>or "F2" to go to the chapter menu.
>Adding a button on the chapter menu to return to the main menu is on my 
>todo list :-)

I think, also, there's some confusion over the meaning of the term "root 
menu."  Many people are under the impression that the menu that appears 
upon initially inserting the DVD is called /the/ root menu.  In fact, 
it's actually the title menu.

A DVD video disc contains at least one Video ManaGer Menu (VMGM) and 
zero or more titlesets.  Video is placed in ProGram Chains (PGC's).  
PGC's may appear within menus (including the VMGM and titleset menus) 
and/or within titles.

Each titleset (I think there can be up to 9) can have any of several 
menus.  There can be zero or one of each type of menu per titleset; i.e. 
a menu could be a root, subtitle (subpicture), audio, angle, or ptt 
menu.  (Where "ptt" means "part of title", but I have no idea which of 
the T's are used for the acronym.)  These probably correspond to buttons 
on your dedicated DVD-player's remote.

The VMGM--because it's a menu--may contain a PGC, but it is /only/ a 
single menu--and it's called /the/ title menu (not subtitle or ptt, just 
plain title--titlesets cannot have a title menu).  Some DVD player 
remotes call the title menu a "DVD menu" or "Disc menu."  So, if you're 
in the VMGM (whatever plays when you first start the DVD) and you select 
the title menu, you'll go to the VMGM title (this can be used, for 
example, to skip over legal notices and other "junk" before the 
menu--although whether doing so is legal in your area is a whole other 

If you're in a titleset and you select the root menu, you'll go to the 
titleset's root menu.  If the titleset doesn't specify a root menu, 
generally the button should do nothing (however most titlesets have a 
root menu because it's the only way to call the title menu from a 
titleset).  If you're in a titleset and you select the title menu, you 
/should/ go to the title menu, but if the VMGM is empty (which results 
in playing the first titleset's menu upon starting the DVD), you'll go 
to the VMGM--which is empty--and continue through to the first 
titleset's root menu.  In this case, title and root menus result in the 
same behavior (even though they're technically different things).  This 
is one of the main reasons for the confusion about what's considered a 
root menu.

To make matters even worse, the DVD spec actually allows the DVD to 
specify commands through a (somewhat primitive) programming language.  
Using these commands, DVD designers can actually override the behavior 
resulting from requesting different menus.  I've actually seen DVD's 
that use this to jump back to the root menu in a titleset after 
requesting the title menu (making me dig my way back up after digging 
down to a video).

Because of this and the fact that there are about a million ways of 
designing the menu structure of any DVD, you basically have to figure 
out the DVD's internal structure to determine how the menus will work.  
And, even then, depending on the DVD in question, it may still behave 
differently from how you expect.

So, in summary, there's only one title menu and each titleset can (and 
probably does have) its own root menu.  Unfortunately, this means the 
DVD spec designers chose a terminology that typically has an intuitive 
meaning to end users that's very different from its real meaning.  And, 
even more dissapointing is the fact that the manufacturers of many DVD 
players used this terminology (root/title) when making their OSD's and 
remotes--generally causing confusion among users (and making them think 
that "something must be broken").

Whether a hacker's DVD player (i.e. xine, possibly MythTV's Internal 
player) should use the spec's terminology (thereby allowing the hacker 
to learn--which is the goal of a true hacker) or should use more 
user-friendly terminology is another question I'll leave to the UI 



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