Open GOP's ?

[JConnor]

When i demux some dvd and try while i insert the celltimes using dvd lab-pro how come i get an error that says that there are open gop's.... actually i needed to know how to close them cuz the time chapters are kinda different and do no not match the original timings.

[adam]

A GOP can be set to open or closed. If closed all P and B frames can only look to frames within that GOP, and if left open they can reference frames from other GOPs. Using open GOPs is more efficient and thus higher quality overall. A typical DVD uses a mixture of open and closed GOPs. Closing all GOPs increases seek times when jumping between chapters and FF/RW but degrades quality. There are only a couple of instances in which you'd want to do this, mainly if you need to author multiangle footage.

A chapter can only be inserted on an I-Frame and then you should close this GOP to increase reference time. If the GOP is left open you can still set the chapter here but it will take longer to seek it, which basically just means it might take longer to jump to that chapter. The reason your chapter times are off is not because the GOPs are open but because (I assume you have re-encoded the footage) your new mpg does not have I frames inserted at the chapter points as was the case with the original. What this does is force your dvd authoring software to insert the chapter at the closest I frame. I would not worry about the open GOP error, there's nothing wrong with this. What you need to do is manually force an I frame at each of your chapter points. Many mpg encoders support this option and you can often import all your chapter points from 3rd party programs like dvd decryptor or IFOEdit.

So...what mpg encoder are you using?

[guns1inger]

It's not an error, it's a warning. Ignore it and proceed without worrying about it.

[JConnor]

All i did was take a normal dvd and demuxed it and when trying then add new subtitles using dvd lab pro and that's all and i assure u that there is a need to worry because the chapters are relaly messed up. Like for example the last few chapters of Nightmare on Elm Street dvd are missing cuz of that error. I didnt have that trouble before untill this message started to come out. And all i need is a simple answer is there a way i can close GOP's or not?

[guns1inger]

That message has been in DVD Lab Pro since the Pro version went gold. The latest version (1.60+) has an option to disable the mssage because it does not affect the way the disc is compiled. If this is just a demux commercial disc, then it already had open GOPs, but as Adam pointed out, probably closed I frames on chapter stops.

[adam]

If you want to close GOPs you have to re-encode the entire movie an tell the encoder to close all GOPs, assuming it has that option. There, that is the answer you wanted but the problem is that you are asking the wrong question...still.

Again, the fact that your GOPs are open cannot possibly be your problem. Whether a GOP is closed or not has absolutley nothing to do with chapter placement. What is more likely is that you are not properly creating and/or importing your chapters. In fact I just noticed something about your initial post. You say you are importing celltimes, but chapters are created via programs not cells. There are often many cells within each program (chapter.) You are importing the wrong thing.

What program are you using to get your "chapter" points, and what specific option did you use?

[JConnor]

Well im using PGC Demux and the celltimes.txt is the only thing i get for chapters to import after i demux it.I also use sometimes use Dvd Decrypter but then i receive 2 files for chapters instead of one Chapter information - DvdLab.txt and Chapter Information - IfoEdit.txt. and ussualy insert the chapter points from the dvdlab.txt