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Everyone Agree on 50Mbps?


Ben Corwin
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In my test results, the GH3 shows much less compression artifacts in IPB 50Mbps mode, than in ALL-I 72Mbps mode.

 

Also confirmed by the great cbrandin himself...

 

"I would expect that the 50Mb long GOP video should look very good on
the GH3 - at least as good as GOP12 at 66Mb on the GH2 - probably even
better.

The 72Mb all I frame video probably won't look very good. At 72Mb GOP1
streams will have small I frames - about 375 kilobytes each. Even at
24Mb a GOP12 stream can have I frames up to around 1 megabyte. I frame
size pretty much limits image quality, and 375 kilobytes just isn't
enough. In order to maintain reasonable individual frame quality, Nick
Driftwood had to push data rates to over 150Mb for some of his all I
frame (GOP1) settings."
-cbrandin

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I am always torn/confused to the benefits/disadvantages of using short and/or longer GOPS. I understand that long GOPs, around 12/15 with IPB frames are best for static shots and lower GOPS are better for motion...but how static is static and how much movement is classed as motion?

 

I film head shots...interviews...weddings etc and most of my 'movement' happens within the frame of a stable non moving camera. Rarely would I do pans or handheld shots but at weddings and similar events there is still a lot of motion going on within the frame.

 

with this in mind would this be classed as static shooting?...therefore more suitable to longer GOPs or is any movement, inside the frame or from the camera itself better suited to shorter GOPs?

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Here's a question to all GH2 and GH3 owners familar with close inspection of the source files, GH2 shot AVCHD only, GH3 offers both AVCHD and h264AVC.

The h264 out of the GH3 appears to have 32x32 or maybe its 64x64 macroblocks, or is that a problem with me using ffmpeg to decompress?

If it is genuinely larger than 16x16 macroblocks with partitioning therein, the standard for h264 then maybe GH3 is using HEVC hybrid h264 encoding, supposedly more efficient and more with the future of higher resolutions in mind.

If that's the case the simplistic comparison of bitrate and GOPs becomes even less a worthwhile measure of 'quality'?

At the moment from the GH3 h264 I've seen I strongly dislike the coarseness of the image which appears to need a heavier hand denoising etc.
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Technically, wouldn't this be because IPB is pulling less detail than ALL-I.....that's the way I always look at this. so it's one or the other. 

 

In fact no. For the same bitrate, IPB should be better on most scene (with low to mid action or little camera movement)

 

Like said, you have a small size for every frame on All-I. You have bigger I frame on IPB, this is important. after that, the other frames are calculated as difference from that I frame. The difference between frame is generaly small, it is like have much higher data on IPB.

 

Personally, I would shot IPB most of the time and switch to All-I when there is a lot of action going on.

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