STC (SCR) discontinuity and pauses in the playback

[tom942]

I've just burned a backup of "The Sting" (R2) and when I was watching it, I noticed that there was a pause.

Initially, I thought it was something related with the layer break, but it wasn´t, because I set it in other place previous to the place where the original one is.

Then, in PGCEdit, I can see in movie's PGC a cell command (LinkTailPGC, button 1 (1024) )and in one of the cells, the "STC (SCR) discontinuity" flag is checked.

Then I compare with other Universal's DVD, "Apolo 13", and it has the same command, but the flag, it is not checked. This one plays without the pause.

In both, the VOBID is the same along all the PCG (1/xx).

Then I've burned again the DVD, and this time it plays without the pause.

But I've got a doubt why happens this, because I've seen other DVD's with this flag checked and they play without the pause.

In these ones, there's no cell command, but there's a change in VOBID (just where is the flag checked). It goes, for instance, from VOBID 1/xx to to VOBID 2/xx.

So, what has happened in "The Sting" DVD?

I suppose that when the player finds this flag and reset to 0 the clock:

1. It executes the command

2. or it is something related with VOBID

Thanks in advance, and sorry if this thing has been talked before, but I've been unable to find it.

Regards,

Tom

[Alex_ander]

Maybe this excerpt from DVDRemake docs helps (a bit different terminology):

Seamless playback:
This is a flag that tells the player to make the transition from the previous cell seamless or without a pause. In most cases cells within a PGC will play seamlessly without this flag being set, but when it is set, it tells the player that the VOB's were prepared in such a way to guarantee that the cells will play seamlessly. Merely setting this flag does not guarantee seamless playback, especially if the blocks that the cells point to are physically located far apart. If this flag is set, no cell command will be executed for the previous cell. For this reason, if a cell command is set for a cell, DvdReMake will automatically clear the seamless flag for the next cell.

Maybe in your case playback (by executing the cell command) explores post-command list for commands, before starting next cell. After your setting flag to seamless it ignores that cell command.

[r0lZ]

That's right. (Good DRM docs BTW!)

Note also that the VOB ID doesn't have to change at the layer break position or when there is a cell command, but many DVD are authored this way.
Theoretically, the seamless flag must be clear at the layer break position, but it is sometimes set to avoid the pause. This technique is used by the Superbit DVDs, and is supported by PgcEdit and ImgBurn. This is non-standard, and may cause problems with some (especially old) players, but in my experience, it's usually OK. On the other hand, the seamless flag must be clear when there is a cell command, or it will not be executed.
The players are supposed to pause when the seamless flag is clear, but some players (especially the software players) do things as fast as possible, and the non-seamless joint might be unnoticeable if the hardware is fast enough, or the buffers large enough.

[tom942]

Sorry, sorry, I don´t just refer to seamless flag :(.

I forgot to add that in the second backup that I have made of "The Sting", I had removed from the movie's PGC the "STC (SCR) discontinuity" flag, in the same way as I saw it on the Apolo 13's DVD, and then this time, there was no pause and plays seamlessly.

But I don´t undestand this behaviour, because I've seen several Warner DVD's, that have "STC (SCR) discontinuity" flag on, but they don´t pause, they also play seamlessly. The differences of these with the above are:

1. No cell commands

2. Two VOBID's in the same PGC (VOBID 1/xx ---> VOBID 2/xx)

I hope to be more clear now and in summary:

Why sometimes with "STC (SCR) discontinuity" flag checked, it pauses and others do not?

Note: Even I've done a test backup with DVDShrink and I told it to not remove the layer break. Then I playedback the DVD and the pause was there. I send it to PGCEdit and "STC (SCR) discontinuity" flag was there. I removed, and the playback was fine, seamlessly.

And yes r0lz, I am trying to mimick Superbit DVD's :).

Thank you for your great app. As soon as I can, I'll try to donate you. I've got to do the same with LIGHTNINGUK, but two weeks ago I bought (following your and others recommendation) Jim Taylor's book and Ralph Lauge one, and now I have to recover my pocket :).

P.S.: All these pauses happen in the standalone player.

[r0lZ]

The STC Discontinuity flag means that the System Time Clock is reset at the beginning of the cell. Normally, it must be set when the VOB ID changes (and of course on the first cell of the PGC), as a new Video OBject begins with new time codes. The presence of this flag does not mean that the playback cannot be seamless, but it is often used in conjunction with the seamless flag clear, for example at the layer break position. The STC flag can also be set if you cut, delete or blank a cell (for example with VobBlanker), and even if the VOB ID doesn't change, because there is a gap in the timecodes between the remaining cells. You should not change this flag.
Anyway, its presence or absence should not be the cause of the pause, but perhaps the player gets confused when it is wrong.
Are you sure there is no cell command? Maybe with some players, a cell command with a seamless flag set causes a pause, even if the cell command should be ignored.

Also, I have seen a DVD with a cell command at the layer break position. This is unusual. This cell command was added by Sony to skip ARccOS protected cells in the middle of the movie. In this case, removing the cell command and setting the seamless flag is not sufficient to get rid of the protected cells. Since they contain junk, a pause may occur, and the player may even crash when it tries to play them.

[tom942]

This the image of PGC's commands:

http://img242.imageshack.us/my.php?image=comandomz5.jpg

As you can see, there's one cell command.

This one shows the flags and when the command is called in the PGC Editor:

http://img242.imageshack.us/my.php?image=flagig0.jpg

As you can see, in V/C ID 1/6 is where the seamless flag in uncheked, where the original layer break is and where the movie pauses, but when I have burned the movie, I have selected the layer break in V/C ID 1/5 (previous one).
At the end of the PGC, you can see that the cell command is called, but it is after the credits.

If I left checked "STC (SCR) discontinuity" flag, it pauses. If I left it unchecked, it doesn´t pause (I know these becuse I mimick the structure of other Universal' DVD, Apolo 13).

Of course in ImgBurn I have checked "seamless" when you have to select a layer break point.

The doubt comes because I've got several Warner DVD's, and in these ones, there's no pause, although in one cell got checked both flags, seamless joint and STC.
But in these ones, there is a different VOB ID (1/xx ---> 2/xx) and there is no cell command.

So, if it is possible, is it better to remove the cell command to avoid pauses instead of just unchecking the STC flag?

[blutach]

The only use of the cell command is in cell 17, which directs the DVD to go to the post commands before the tiny 12 frame blank cell is played. Don't worry about it.

If this is an original DVD, I'm not sure why the STC is reset on cell 6. I'd change the flag to 8 and it should play seamlessly.

Regards

[r0lZ]

Yes, the STC discontinuity should not be set on cell 6.

I don't know exactly if ImgBurn modifies the seamless flags of all cells, but PgcEdit's burn function modifies only the layer break cell, either to set or remove the seamless flag according to the "seamless layer break" option. The other flags are unchanged. So, you probably have to manually set the seamless flags on cell 6 before burning. A good ripper should set it automatically anyway during the ripping phase, but iirc, it's an option in DVD Decrypter.

Anyway, in this case, cell 6 should have exactly the same flags than cell 7, because there is no VOB ID change implying a STC discontinuity and it is not used any more for the layer break. The pause is probably caused only by the seamless flag and imo setting the STC flag is not a big problem, but it is better to clear it anyway.

As Blu said, the cell command is not responsible of the problem, as its pause occurs at the very end of the movie, and should be unnoticeable.

[tom942]

Yes, it is an original one. It was ripped first with DVDShrink (no compression) and later with AnyDVD. Always the same STC flag in that VOB ID.

Also I've got other one, "Jurassic Park", and this one has a worse authoring, because first it ignores the preferred audio and second, there is a command (NOP) just in the layer break (I can see in PGC Editor that it points to), so it makes a little pause.

By the way, I have imitated with the Warner ones the setting of the "STC" flag in middle of a VOB ID, and yes, it does a pause, even on Media Player Classic. However, in the VOB ID change they don´t do the pause. So, I'll do for future backups what you said Blutach. To check the flags if there are any extrange.

I supposed that like they are comercial authorings, then they were done properly, without errors like this :).

Thank you for the help :).

Edit: I didn´t see r0lz's answer, because I was answering at the same time.

[tom942]

The image posted in #6, is the DVD just ripped to HDD. (http://img242.imageshack.us/my.php?image=flagig0.jpg)

This one is the first burned DVD, but with pause:

http://img518.imageshack.us/my.php?image=dvdwithpauseep4.jpg

and this one is the second burned DVD, this time already without pause (unchecking STC flag before burn):

http://img88.imageshack.us/my.php?image=dvdwithoutpausece7.jpg

Both are DVD+R DL.

I ask this, because I'm learning to burn DL DVD's, and I want to avoid errors, because these ones are not precisely cheap :).

[r0lZ]

Well, I'm puzzled, as the pause should not occur with the first try. Maybe it's something with your player. I don't understand why the STC discontinuity flag was set in the original DVD.

Anyway, the second burned DVD is perfect: seamless flag on and STC discontinuity off since there is no VOB ID change.

[tom942]

It was set in the layer break, in middle of a scene when Billie and the cop Schnider were talking. No scene change or something similar to disimulate it. Strange authoring, you see... :). And it is a DVD release of 2005 :o.

More than a pause where it freezes and then follows the playback, it is like a jump, there is a loss in continuity. She starts to move down her hand and suddeny it jumps then it is on the cop's hand.

My player it's a Panasonic s52. I'll try in it an old one that I've got retired (JVC), to see how it behaves.

But the tests that I did with Warner DVD's of the post above, when I modified them and set STC flag in middle of VOB ID, also shown this kind of "jump" in MPC player.

Sorry r0lz, I don´t want to get you nuts (or crazy, don´t know the right word) :)

[blutach]

nuts is good :)

Sometimes, the commercial authoring packages get things a bit haywire. Anyway, you know now, that STC changes essentially on a Vob ID change there are other instances) and the seamless flag is the one which inserts a pause or not.

If you burn with ImgBurn (www.imgburn.com), it has a preview so you can choose for youself where to place the layer break, and an option to make the burn seamless (PgcEdit has this too, of course).

Regards

[mikenadia]

Straight from the rip.
http://img292.imageshack.us/img292/6416/flagll7.th.jpg (http://img292.imageshack.us/my.php?image=flagll7.jpg)

********** post commands:
[61 00 00 0C 00 81 00 00] 1 Set gprm(12) =(mov) sprm(1:Audio stream number)
[61 00 00 0D 00 82 00 00] 2 Set gprm(13) =(mov) sprm(2:Sub-picture stream number)
[71 00 00 0F 00 63 00 00] 3 Set gprm(15) =(mov) 99
[30 08 00 11 01 C0 00 00] 4 (CallSS) Call the VMGM PGC 17, resume cell 1
********** cell commands:
[00 00 00 00 00 00 00 00] 1 NOP

I have to uncheck seamless joint in cell 20, but can I delete the cell command (NOP) and put the cell cmd # in cell 19 to 0 (instead of 1)?

Thanks in advance.

[blutach]

Yes. And then you can keep it seamless (if you wish and your player supports seamless layer break).

Regards

[r0lZ]

A cell command in the middle of the main movie is very unusual. I've seen that only once, in a protected DVD, where the cell command was used to ship some protected cells at the layer break position. But in your case, I see no reason to execute a NOP during the layer break, as NOP does nothing. And, according to your screenshot, the two cells around the LB are contiguous, so there is no protected cells in the middle of the movie.

Remove the useless cell command!

[blutach]

I've seen it a bit - I think it's an authoring technique to ensure a pause at the layer break (although a non-seamless joint would usually suffice).

Regards

[r0lZ]

I wonder why they want a pause. If the player can skip it, why not?

[jinjin_jp]

A cell command in the middle of the main movie is very unusual. I've seen that only once, in a protected DVD, where the cell command was used to ship some protected cells at the layer break position. But in your case, I see no reason to execute a NOP during the layer break, as NOP does nothing. And, according to your screenshot, the two cells around the LB are contiguous, so there is no protected cells in the middle of the movie.
I have the memory of cell command in middle, so confirmed and found some examples.
They were all Sony-picture's, last cell in layer-0, and not seamless.
http://img292.imageshack.us/img292/6046/cellcommandxm6.th.png (http://img292.imageshack.us/my.php?image=cellcommandxm6.png)

Regards.

[r0lZ]

Yes, indeed, I was wrong, and this technique is used often. But I still wonder why! Given the fact that they are $ony releases, I suppose this could be a sort of weak protection, to prevent the rippers or DVDShrink to remove the layer break pause.

[blutach]

However, IIRC, mikenadia's DVD showed no such discontinuity.

Regards