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Old February 4th, 2007, 09:58 AM   #1
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HD100 short GOP vs HD200 long GOP

I was wondering about the differences between the GOPs of the two camera lines, specifically what does it mean for:
1. Matching HD100s with HD200s in multicamera environment
2. Using footage from both in the same timeline (will the NLE have a problem with this?)
3. Does HD200 record in 12 GOP even in HDV30p mode?
4. Any other concerns?

Thanks.
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Old February 4th, 2007, 11:38 AM   #2
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Quote:
Originally Posted by Jiri Bakala
I was wondering about the differences between the GOPs of the two camera lines, specifically what does it mean for:
1. Matching HD100s with HD200s in multicamera environment
Should be easy. Just adjust the HD200 to match the HD100 settings.
Quote:
Originally Posted by Jiri Bakala
2. Using footage from both in the same timeline (will the NLE have a problem with this?)
If both cameras shot at the same frame rate then there SHOULD be absolutely no issues.
Quote:
Originally Posted by Jiri Bakala
3. Does HD200 record in 12 GOP even in HDV30p mode?
That is a good question. I assume 12 frame GOP structure is only used with 50P and 60P, but I could be wrong. 6 frame GOP worked so well in 24P, 25P and 30P that I would be confused by an engineering choice to double the length of the GOP.
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Originally Posted by Jiri Bakala
4. Any other concerns?
I doubt it. I'm picking up a HD250 soon and I will add this to my list of items to explore.
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Old February 4th, 2007, 02:21 PM   #3
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Thanks Tim, check that fan noise when you have the HD250...
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Old February 6th, 2007, 08:33 AM   #4
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Quote:
Originally Posted by Jiri Bakala
3. Does HD200 record in 12 GOP even in HDV30p mode?
Thanks.
No, because if it did, it would no longer be compatible with your existing 720/30p codecs on you NLE.

I'm not sure if the HD200/250 "super encoder" makes a difference at the slower frame rates.
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Old February 7th, 2007, 01:42 AM   #5
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Originally Posted by Tim Dashwood
6 frame GOP worked so well in 24P, 25P and 30P that I would be confused by an engineering choice to double the length of the GOP.
I agree - and this has been a concern for me. Can we get some official announcement on that somewhere, because no one seems to know for sure... ?
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Old February 7th, 2007, 03:17 AM   #6
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There was a discussion on this quite awhile back. In that discussion -- and I don't know by whom -- it was said that 24p and 30 were still 6 GOP and the 60p was 12 GOP.

The 12 GOP 60p was to transmit as much data per second as the 6 GOP in 30p mode.

The standard is the 19mbps (or however it is written) rate. The 12 GOP in the 60p is necessay to keep the same amount of data in the stream per second.

This is just from memory, but I remember that at the time it was pretty clearly stated by someone who shuld have known.
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Old February 7th, 2007, 06:51 AM   #7
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I asked this question some time back and never got a solid answer as to whether the super encoder had a strong benefit for the 24/30p modes. As far as the GOP goes it isn't a simple matter of going from a 6 to 12 GOP to get double the frame rate. The 480p60 mode used a 12GOP to equal the same bit rate as 720p30. Jumping to 720p60 using this same logic would require a great deal more then 12 GOP, which is just proof how powerful the super encoder is. To double the frame rate at the same resolution while only doubling the GOP while improving the picture quality is unbelievable.
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Old February 9th, 2007, 06:45 AM   #8
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Long GOP

Ken, and others,
the increase from GOP 6 in 720/25P...30P mode to GOP 12/50P ...60P is sufficient to handle the additional information coming from 50P ... 60P. Please observe, that with higher framerate the differnces between each individual frame become much smaller (one can say it is about 1/2). The encoder considers only diffential information between frames (following the full encoded I-frame of the group), which is relatively small. Therefore the increase to GOP 12 fully covers the additiional information requirements for 50P/60P. The only disadvantage is, that in case of a drop-out in an I-frame the whole group of 12 (as instead of 6) frames becomes erronous.
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Joachim
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Old February 10th, 2007, 12:58 AM   #9
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No its not sufficient to just double the GOP. The super encoder is what makes it possible.
As I already mentioned, if you look at the HD100 or the older HD10 the 720p30 mode (6GOP) and the 480p60 mode (12GOP) use the exact same bandwidth. 720p60, no matter what the GOP, just wasn't fez able until the super encoder was developed. If simply extending the GOP allowed doubling of frame rates, they wouldn't have been stuck at 480p60 until now.
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