Commerical DVD Playback Restrictions

[Zach]

Sorry about the title, but I'm not sure how to title this succinctly.

I have a question for you DVD authoring experts. (This is a general question, though, hence why I posted it in this forum.)

I'm sort of a DVD-holic (:p) in that I tend to buy a lot of DVD's just as impulse items. (I'm at some store; I see a DVD with an interesting title or cover art; and so I buy it on a whim.)

Here's what I'm wondering about. As do probably all DVD players I think, my DVD player has a memory feature that allows me to stop playback (and even power down if I like), and then later resume where I left off. (This comes in handy since I tend to watch movies as an aid to help me get sleepy, and so I'll eventually stop playback somewhere in the middle.)

Here's the thing. This doesn't work with all DVD's. Why is that? All major releases always work fine, but DVD's of B movies (or bargain bin movies) half the time won't start where I left off, i.e., pressing Play again makes the DVD player act like I just inserted the disc for the first time and starts over at the beginning.

What puzzles me is that these DVD's usually are normal in every other sense in that they have the standard menu with trailers, extras, audio selection (sometimes), and most importantly, scene/chapter selection. Because of this, I am thinking maybe this is some sort of restriction embedded in the DVD. (I don't know anything about the authoring of commercial DVD's, but I know there are flags and such that disable the skipping of the intro stuff [like the FBI warning] and things like that.)

So is there some flag set on the DVD that prohibits stopping a movie and then resuming later, and if so, what would be the purpose of such a flag?

[zacoz]

Zach, I know of the function that you speak, however don't know how widespread the function is amongst new players nor exactly how it works. On my new Omni player, the function supposedly works even if the disc is taken out and player placed in standby, but not if it is switched off with the "hard" power button. Might it be that on those it didn't work on you powered system off rather than placing in standby mode ?

I'm unaware of any flags (eg Prohibitited User Operations) that would stop it from working. It possibly comes down to how the player stores the record of where it was up to. I'm thinking that if it in fact stores the gprm & sprm register values, then it would only be able to continue from the same point if the DVD was 'programmed' to support resuming. So on inserting disc the player recognises it and instead of clearing register values it uses those previously stored. As the DVD commands then execute it uses these register values results in DVD resuming from stopped point. I can understand how this would not work for all DVD's, as I've seen some DVD's where the actual DVD commands set the registers to zero at the start rather than relying on the player to do so - this of course immediately overwrites the stored values initially fed by the player.

May require someone with a bit of knowledge in regards to the firmware of the players to confirm how this functionality works.

[Zach]

Might it be that on those it didn't work on you powered system off rather than placing in standby mode ?

No, not likely. My current DVD player is actually a DVD recorder which acts as the liason between my satellite receiver and TV, so because of this, I usually (99.9% of the time) just pause the DVD and then switch back to hard drive mode--at which point I'll power down the satellite receiver and TV, but not the DVD recorder.

Anyway, this "resetting" anamoly has been present for every DVD player I've own, namely, four players (two Sony's, a Panasonic, and a Toshiba) and my current Panasonic E85 recorder, hence why I am suspecting that it has something to do with the disc itself and the way it was authored and not the player itself.

Your thoughts about the gprm & sprm register values seem like a good explanation though. :) Thanks for satisfying my curiosity!