MPEG document describing 'open GOP' in detail?

[Alex_ander]

There can be found 2 absolutely different definitions for 'open GOP':

1. A GOP which uses referenced pictures from the previous GOP at the current GOP boundary. For example the GOP is open when B Frames at the start of a GOP rely on I or P frames from the immediately previous GOP.
( https://www.videohelp.com/glossary?O#Open%20GOP )

2. A GOP just ending with B-frames and needing I-frame of the next GOP for decoding (the rest as with closed GOP). Often used in forums as self-explanatory thing.

I tend to believe the first concept is true as some independent sources confirm it:

http://forum.doom9.org/showthread.php?p=673538#post673538
http://www.patentstorm.us/patents/6393057/description.html

Can I find on the web any official MPEG document on this with detailed open GOP description (dependencies between frames etc.)? The one linked from MPEG.org doesn't even mention 'closed'/'open' terms.

[Cornucopia]

The 2nd one is true. The 1st one is not possible.

GOPs ALWAYS start with an I-Frame.

I have documentation to support this, but am not on that computer right now.

Scott

[aedipuss]

1 and 2 mean the same thing. a GOP is "open" if it references anything in another GOP. a closed GOP only references picture changes within itself.

[Alex_ander]

1 and 2 mean the same thing.

The first one is different since mentions reference from first B-frames of a current GOP to some frames before I-frame of that GOP which is strange at least (Cornucopia says impossible). So is the USA patent #6393057 (from my last link) absolute nonsense?

[hank315]

Depends what your definition of frame order is.
1. stream order
2. display order

Normally, stream order is used.

The definition is here, page 46

[Alex_ander]

The definition is here, page 46

Thank you. Could you quote it please? The document is only available by subscription/purchase and its earlier downloadable version doesn't define open GOP. Or is it defined the same as in Videohelp Glossary?

[hank315]

Thank you. Could you quote it please? The document is only available by subscription/purchase and its earlier downloadable version doesn't define open GOP. Or is it defined the same as in Videohelp Glossary?

The PDF document can be downloaded for free, it's the latest MPEG2 standard AFAIK.

[Alex_ander]

Thanks again, got it now.