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Do video assets have to have "closed GOP"?

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chris lambertDo video assets have to have "closed GOP"?
by on Sep 28, 2004 at 10:11:50 pm

have a post a little further down, but basically DVD SP2 crashes whenever I try to build. Did some troubleshooting, and noticed that whenever I use only video assets that have a closed GOP it builds OK, but when i use some video assets that don't have closed GOP it crashes when i try to build. Is that a coincidence or are non closed GOP clips problematic? and is there something in compressor that can give a clip a closed GOP?

Thanks for any help - Chris


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sacciRe: Do video assets have to have "closed GOP"?
by on Sep 29, 2004 at 7:30:11 pm

It is always better to use a Closed GOP structure. The only time an open (non-closed) as any benefit is on very low bitrate encodes (below 3 Mbps) and the benefit is very minor, one get one extra B frame (bi-directional) over against the P Frame (predictive). It is best to stay away from them totally.

You set the GOP structure in the presets Encoder: MPEG-2 and GOP tab. You want 1BBP Closed
Size 15 if NTSC or 12 if PAL (normally)

The close thing is compressor shows you the pattern that you get under each setting.


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chris lambertNote: don't mix open and closed GOP structures!
by on Sep 29, 2004 at 8:09:38 pm

thanks for the info. once I changed all my video to closed GOP it built fine. what happened is that in Compressor if you change the setting from Automatic to NTSC, for some reason it quietly changes your GOP to open. didn't notice that till today. of course according to the manual you can mix open and closed GOP structures, unless you're doing mixed-angle stuff, but that definitely doesn't work on my computer, and i'm curious if it's just a glitch on my system, or if it's a glitch in DVDSP2. can anyone else run a test and see if you can mix open and closed GOP? might want to let apple know if it's a repeatable glitch.

Also, if I'm doing a short film and quality is more important than file size, should I do IBP and a small GOP of 6? Wouldn't that give me more I frames, less B-frames, and thus better quality?

Thanks a lot - chris


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NeilRe: Do video assets have to have "closed GOP"?
by on Oct 4, 2004 at 6:57:19 am

[sacci] "It is always better to use a Closed GOP structure"

ummm ... the defaults in Mediapress 1.2 are Open structure.
I wonder why?


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sacciRe: Do video assets have to have "closed GOP"?
by on Oct 6, 2004 at 3:44:38 pm

Open GOPs are a method of squeezing a little more quality out of low bit rates but there are just too many problems that seem to pop up with using them. Given the chance to choose I would never recommend using them (open GOP).


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