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Old 15th November 2014, 00:31   #1  |  Link
Lyris
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Failsafe commands in PGCs

Hey all,
I've noticed that a lot of discs have commands at the top of (nearly) every single PGC in the disc that kick the user back to the beginning (First Play PGC, Copyright warning etc) if certain conditions are not met.

Is this to defeat Resume functionality in players? I've never quite got my head around why these commands are there.

Can anyone advise?
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Old 15th November 2014, 18:39   #2  |  Link
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Hard to guess without seeing the code... Which companies ?
Given the many different (and some faulty) implementations of hardware player chipsets (SPRM7 comes into mind)
I would guess this kind of coding might serve as fire exit on the authoring side for players that might lock up on certain conditions.
The defeat of Resume might be taken here as the lesser damage.
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Old 16th November 2014, 12:44   #3  |  Link
TheSkiller
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Quote:
Originally Posted by Lyris View Post
Is this to defeat Resume functionality in players?
In the first Titleset of a DVD (VTS_01) it's pretty much certainly there to make the player act as if the DVD was just inserted whenever the user pushes Stop twice during playback and then pushes Play to start again.

Reason is, without such code, after pressing Stop twice and then Play, players would just start playing VTS_01 no matter what. So without the code the First Play PGC is only executed after the disc has been inserted, not after pressing Stop twice.
Playing VTS_01 straight without any menu etc. wouldn't make much sense most of the time so you often find code like that in the pre-commands of VTS_01 or you will find that VTS_01 is just a dummy with 1 second of blackness to catch this behaviour.

Last edited by TheSkiller; 16th November 2014 at 12:47.
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Old 20th November 2014, 21:32   #4  |  Link
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In the first Titleset of a DVD (VTS_01) it's pretty much certainly there to make the player act as if the DVD was just inserted whenever the user pushes Stop twice during playback and then pushes Play to start again.
Never heard of that. Isn't pressing stop twice supposed to reset the VM and infact let the player act as if the disc was just inserted when the user presses play again? If you don't want this, you would press stop only once anyway.
I'm curious. I should build a test DVD to chech that out.

My best guess would be that those commands are there to enforce you to watch all the legal pages (and sometimes even more annoying stuff) before you can do anything else. It certainly is an effective way of defeating UOP free players.
I've also seen DVDs which have a separate PGC with identical cell arrangements for each language. Each with only one audio and one subtitle track assigned. That also is certainly a measure to defeat UOP free players and ensure forced subtitles on certain dubbed versions.
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Old 20th November 2014, 22:57   #5  |  Link
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Interesting, my SEG player indeed starts right at VTS1 after pressing stop twice. My Panasonic even does this when I press stop only once. And my PS3 does this when pressing stop while on a menu. They all reset the registers when starting at VTS1 this way.

What is the point in this behavior? It just seems like a way to break things.
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Old 21st November 2014, 17:36   #6  |  Link
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Quote:
Originally Posted by LogicDeLuxe View Post
Isn't pressing stop twice supposed to reset the VM and infact let the player act as if the disc was just inserted when the user presses play again? If you don't want this, you would press stop only once anyway.
That's what one with a right mind would expect, but as you have discovered players do not behave like that (this seems to be standards compliant though, at least I have never seen a player behave any different upon pressing Stop twice).

Pressing Stop twice and then Play will make the player start playing VTS_01 regardless of what the First Play PGC says, unless the pre-commands in VTS_01 direct the player somewhere else, usually with the help of a GPRM so that the Titlset starts playing only after it has been called from a menu.


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Originally Posted by LogicDeLuxe View Post
My best guess would be that those commands are there to enforce you to watch all the legal pages (and sometimes even more annoying stuff) before you can do anything else.
That certainly does explain why the commands are in the pre-commands sections of every VTS. From a technical point of view they make sense in the first VTS (to catch the pressing Stop twice behavior) but not really anywhere else, unless you really want to enforce the viewing of the legal pages in case the player does not obey the PUOs/UOPs and let's the user play a VTS right away without the DVD's menu.


Just curious, does the PS3 also start playing VTS_01 upon pressing Stop twice while not in a menu, while playing a VTS?


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Originally Posted by LogicDeLuxe View Post
What is the point in this behavior? It just seems like a way to break things.
I don't know what's the point, but it's a pain in the back when authoring a disc because every time you need to "fix" this behavior again and again. I have noticed a few commercial DVDs apparently do not care about this, so VTS_01 will just play (most do care however).

Last edited by TheSkiller; 21st November 2014 at 17:47.
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Old 22nd November 2014, 23:25   #7  |  Link
LogicDeLuxe
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Just curious, does the PS3 also start playing VTS_01 upon pressing Stop twice while not in a menu, while playing a VTS?
It seems, this useless double stop feature is not implemented there at all.

Pressing stop once immediately quits the player software, thus pressing it again has no effect.

If you press stop while playing a movie, the PS3 remembers all the registers. You can even eject the disc or turn off the PS3, and the movie will still continue where it was the next time you start the DVD. Pretty useful with TV shows if you don't want to watch the same pages and menus every single time.

If you press stop while in a menu, the VM resets and the DVD always starts with first play PGC the next time.

Quote:
I don't know what's the point, but it's a pain in the back when authoring a disc because every time you need to "fix" this behavior again and again. I have noticed a few commercial DVDs apparently do not care about this, so VTS_01 will just play (most do care however).
How often would one press stop twice anyway? I bet, most people won't even realize that this actually does something.

The only occasion, I press stop twice, is to enter the player's system setup (which also uses the menu button) while a DVD is in the drive. And I know people who don't even know how to do that.
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