Open GOPs warning from DVD-lab PRO v1.53

[DRP]

Is anyone else getting a new "Open GOPs warning" from DVD-lab PRO when importing an MPEG made with TMPGEnc Plus 2.5?

I'm just ignoring it and it makes no difference at all, but I'm just curious as to what it's about. It's not a warning I've seen before v1.53 and I've changed nothing in the way I do my encodes. The warning recommends that I choose "close GOP" in my encoder but I can't find such an option in TMPGEnc.

Is this a false warning detection in v1.53 of DVD-lab PRO or am I really doing something wrong in the way I encode/author?

[guns1inger]

I do close them in CCE, but I still get the warning. I'm not sure that DLP is correct on this. As it is a warning I just OK past it and author.

[DRP]

Yeah I do the same and as I said the end result works perfectly just like with all previous versions of DLP. I'm thinking this is a new bug introduced with the release of DLP v1.53.

[reboot]

In tmpgenc, look on the "GOP structure" tab.
There's a tick box for closed GOP.

[DRP]

Thanks very much for that reboot. I hadn't noticed that before. To be honest I don't actually understand GOP Structures at all, so where that's concerned I've been happy to just go with the defaults thus far.

From the TMPGEnc help I get this:

"Closed GOP" 
Enable this if one is planning to reedit the file with other software. This option removes data dependencies between GOPs. 

Checking this option removes the "B" picture dependencies from the GOP which causes and increase in file size.

I can't ascertain from that description what effect enabling this option will have on encoding quality (if any). Can anyone in here with a better knowledge of GOP Structures please explain if closed GOPs has any effect on picture quality for me?

From the TMPGEnc help and from what DVD-lab PRO tells me, a closed GOP Structure is desireable if you then want to re-edit the encode again with other software afterwards or if you plan on inserting chapter points and you want those chapter points to be placed as accurately as possible. That much I understand, but do you sacrifice some encoding quality to gain these benefits?

[manono]

Hi-

please explain if closed GOPs has any effect on picture quality for me?

I keep mine open, although I'm not 100% sure that's the correct way to encode. In any event, closing them makes for a larger file size. Or put another way, if encoding for a fixed file size (like a DVDR), the quality will be very slightly lower. I'm fairly certain it wouldn't be noticeable, but your average quant will be a bit higher. I haven't compared encodings, one with open GOP and one with closed GOP, to see how much higher the average quant would be. For what it's worth, CCE recommends keeping them open. It closes them anyway at scene changes. I don't know how TMPGEnc handles open GOP at scene changes, but it's probably the same.

[DRP]

Thanks for that. I think I have in my mind a good enough idea of what's going on now. I agree with you that closing them probably does result in an imperceptibly lower quality encode for a given fixed filesize.

I'll keep doing what I've been doing and just ignore the warning that DVD-lab PRO is giving me because I always encode to fill the space available, never re-edit after encoding and rarely add chapters to my encodes anyway.

[adam]

When encoding your movie is broken up into many "groups of pictures" and handled independantly. B pictures are bidirectional meaning that they draw information both from future as well as past encoded B frames and I frames. If your GOPs are open you can reference information from all past B and I frames. If your GOPs are closed you can only reference those B and I Frames within your GOP. This means that any information present across GOPs gets restored each time.

Long story short, with closed GOPs you are storing the same information multiple times. Its very inefficient.

Unless you have to edit the mpg for some reason, or are encoding for mulit-angle features, you should always leave GOPs open.

[reboot]

If you want ultimate quality (at the cost of larger files), set a GOP of 1, I frame only.

[ChrissyBoy]

Unless you have to edit the mpg for some reason, or are encoding for mulit-angle features, you should always leave GOPs open.

This is true. For DVD authoring closed GOPs are only MANDATORY for multi angle compilations. I don't use DVDLab these days but maybe it is being pedantic on this issue... Don't get me wrong it is awsome software. It sounds like it is just a warning...

[ChrissyBoy]

The only other thing i can think of as to why there is such a warning is that it is good to have a closed GOP at chapter points but again it is not mandatory in the dvd specs.

[ForceGrown]

I am facing the same problem.
Anybody knows how to close GOPs with DVD Decrypter?

Thanks in Advance.

[fravel]

If you don't want to be bothered by that again, in DVD-Lab PRO just go to Project Properties > Advanced and be sure that "Warn if Open GOP detected" is unticked.

[guns1inger]

fravel : this was introduced in 1.55 onwards (and didn't always work, looking at the change logs).

ForceGrown : DVD Decrypter isn't an encoder and cannot close GOPs.

To anyone still getting this message, upgrade to 1.60.x and you can turn it off.