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Old April 2nd, 2010, 02:42 AM   #1
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Pro,s and Cons iframe /long GOP

Any words of wisdom re the above..

Thanks
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Old April 2nd, 2010, 05:15 AM   #2
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Yes,
This has been discussed at length in a few threads on this forum Robin. So you can get a quick answer to this and any other queries you have - and you should ask, try the search utility and type in the key words.

You will have pretty much all the answers you want in an instant.

Cheers
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Old April 2nd, 2010, 05:36 AM   #3
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Dear Robin,

Here are some guidelines:

At lower bit rates, Long-GOP has a definite advantage in quality, as it is approximately 2 to 2.5 times more efficient.

Putting it differently, at 100 Mbps, Long-GOP is much better than I-Frame.

50 Mbps Long-GOP is much better than 100 Mbps I-Frame.

We currently do not offer any I-Frame Only bit-rates less than 100 Mbps due to quality concerns.

Sony XDCam EX (35 Mbps 4:2:0) has proven how nice 35 Mbps Long-GOP can be, as it has proven how great XDCam 50 Mbps 4:2:2 Long-GOP can be.

Our 100 Mbps 4:2:2 Long-GOP is still the sweet spot and is far superior to DVCPro HD 100 especially in 1080 modes.


From a practical standpoint, for the highest bit rates:

280 Mbps I-Frame is just ever so slighly better than 180 Mbps Long-GOP

I do not have enough data, at this moment, to comment on 180 Mbps Long-GOP versus 180 Mbps I-Frame.


Our Long-GOP's ease of editing must not be confused with the ease of editing (or lack thereof) of editing HDV.

Ours is always full raster (for 1080 this means full 1920 x 1080) and this means that our Long-GOP is much easier to edit than 1440 x 1080 Long-GOP, such as HDV.
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Old April 2nd, 2010, 09:04 AM   #4
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Quote:
Originally Posted by Dan Keaton View Post
Our Long-GOP's ease of editing must not be confused with the ease of editing (or lack thereof) of editing HDV.
Ours is always full raster (for 1080 this means full 1920 x 1080) and this means that our Long-GOP is much easier to edit than 1440 x 1080 Long-GOP, such as HDV.
Just to add to Dan's post... Of course the Nano does do HDV (25 Mbps, 1440x1080, 4:2:0) if you choose to use that low data rate for a long run time...but most people would use the Nano for a gain in image quality, which means you're going to be in full raster 4:2:2.

Even HDV has gotten easier to edit in the last couple years. MPEG as a codec was developed to be used on both the encode and decode side with proprietary hardware...dedicated to simply working with MPEG. A computer CPU was comparatively clumsy at executing the necessary instructions to handle MPEG quickly and efficiently. Frankly, MPEG probably still isn't suited wonderfully for a computer CPU, it's just that the brute force available in the CPUs has increased so heavily that it simply out-muscles it. Digging a hole with a hammer is incredibly inefficient, but if you need a relatively small hole and you have a massive hammer...you can still get the job done.

Long GOP material will continue to be more taxing to handle because the frames have to be encoded and decoded out of linear order. Certainly the edit systems that tried to take HDV's non-square pixels at 1440 and interpolate them on the fly on playback had their hands full with that operation alone, but just as FCP decided to simply run DVCPro at 960x540 and edit it that way rather than waste CPU cycles on scaling up and down...HDV is typically handled pixel-native on most NLEs these days.

Long GOP remains, as Dan mentions, far more efficient than I-frame codecs. It's why 35 Mbps XDcam and 100 Mbps AVC Intra (an I-frame codec) can run in the same circles in every sense other than bit depth (MPEG in the common applications we all use including XDcam and the Nano are limited to 8 bit while AVC Intra can go to 10 bit color precision...however further pressuring the compression scheme) provided the cameras used on the front end are relatively even matched.
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Old April 2nd, 2010, 10:01 AM   #5
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I ask because I got a request to shoot 1080i 50i at 100 Mbps i frame.Iam shooting on my HDX900.Ive only used long GOP before.

I wont be doing the editing..
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Old April 2nd, 2010, 10:05 AM   #6
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Your camera only records I frame to tape...DVCProHD.

Are you saying you typically only record to the Nano?
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Old April 2nd, 2010, 11:07 AM   #7
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Only done one job with the Nano... recorded tape and nano.. but end of last day.. on not so critical stuff.. we just recorded straight to nano..

program is finished .. without ever using the tapes.. but was good peace of mind..

I wonder also.. are there people only recording to nano.. or is there not that confidence level yet?
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Old April 2nd, 2010, 11:15 AM   #8
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Dear Robin,

It is your choice.

Even in a perfect world, with a 100% reliable nanoFlash, having a backup is almost always desirable.
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Old April 2nd, 2010, 12:15 PM   #9
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Just one thing I would add re 8 bit v 10 bit. You will only get an advantage out of a 10 bit codec over 8 bit if the cameras noise level is significantly lower than the codecs sample size. In practice this means you need a really quiet (noise free) camera to make the extra data generated by a 10 bit codec useful. Most of the current HD cameras are not clean enough to bring any significant advantage by recording 10 bit.
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Old April 2nd, 2010, 04:17 PM   #10
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Quote:
Originally Posted by Robin Probyn View Post
I wonder also.. are there people only recording to nano.. or is there not that confidence level yet?
Record to the nano and whatever format your camera uses normally (dual recording). However, use the nano recordings as your primary footage if you have set it to record at a better rate than the camera's recording format.
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Old April 2nd, 2010, 04:19 PM   #11
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Quote:
Originally Posted by Robin Probyn View Post
I ask because I got a request to shoot 1080i 50i at 100 Mbps i frame.Iam shooting on my HDX900.Ive only used long GOP before.

I wont be doing the editing..
Why don't you do some sample test recordings in that way and post your observations? Maybe test between I & LGOP and then show the producer the results.
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Old April 2nd, 2010, 07:28 PM   #12
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Its the production companies standard settings for Nano use.. but thats usually with an EX3
I,ll be shooting with my HDX900.. not a big deal.. just wondered why some people like long GOP and some want i frame..
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Old April 2nd, 2010, 07:30 PM   #13
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Originally Posted by Dan Keaton View Post
Dear Robin,

It is your choice.

Even in a perfect world, with a 100% reliable nanoFlash, having a backup is almost always desirable.
Hi Dan

Yes not casting aspersions.. just wondering if there are lots of people recording just to the nano
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Old April 3rd, 2010, 03:27 AM   #14
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When I shoot 3D I just use the Nano's as they start and stop in sync via the cable that CD made for me.

For me it's comes down to the fact that I can shoot at 100Mb/s long GoP and get quality that is as good as if not better than 220Mb/s I frame, but my media lasts twice as long, long term storage takes less space and copying files takes half as long. In the edit I hardly notice any performance difference. So there are genuine cost and time savings by using long GoP without any image quality implications.
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Old April 3rd, 2010, 05:38 PM   #15
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I would always record to the internal recorder even with a Nano hooked up. You could much more easily have someone accidentally pull out the wires, especially the consumer grade HDMI connectors from the Nano if you aren't careful. Now lots of times you will have the Nano mounted securely, but because it is outboard, especially in the field I would always run the backup.

Remember that once you verify the integrity of the recorded Nano files, you can always delete the backup recordings, although I keep them anyway.
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