GH4 HD: 200 - 100 - 50 file sizes question?

W

wwjd

Well-known member
testing HD bit rate sizes :

4 second file
200mb 5 seconds = 38MB total bitrate 63,000kbps
100mb 4 seconds = 43MB total bitrate 70,000kbps
50mb 4 seconds = 26MB total bitrate 43,000kbps

Other than the one second difference (which should have made it BIGGER) why is 200m bitrate smaller than the 100? and shows less kbps?

I must not understand something here.
 
Bump on this.

I just ran some tests to prep for a shoot tomorrow and I am having the same issue. I am shooting 1080 (at clients request) 30p in .mov and wanted to use the FHD 200M option to give them the most data. I just ran my own comparison and here is what I see.

FHD 200M/All-I Actual result=82Mbps
FHD 100M Actual result=93Mbps
FHD 50M Actual Result=49Mbps

From what I understand the bitrate fluctuates depending on what you are shooting. These were basic handheld pans around my yard for about 20 seconds each. How is it that the 200M is lower than the 100M setting?

Is there another option I am missing or does the All-I only give you those bitrates when the footage is really taxing? It still seems the 200M setting should have at least broken 100Mbps.

Any insight would be appreciated.

Cole
 
Was your test on v2.0 firmware?


http://www.dslrvideocollege.com/all-i-vs-ipb-what-do-they-mean
I found this explanation, seems decent, but doesn't explain WHY gh4 files seem smaller in the ALL-I option. The article says ALL-I is better quality AND larger files than IPB. maybe it is movement related that affects the compression?

Also, I have not tested HD since firmware 2.0, they seem to have adjusted the output of 4k from 70s up to 95s kbps, maybe they fixed HD also?
 
I don't have a GH4 and cannot answer directly. However, it may depend on the frame rate. In a long-GoP codec, it's usually expressed in terms of the overall bitrate regardless of the fps, so ... 1080/24p and 1080/30p can both be stated as 24 megabits, and both will actually be about 24 megabits. In long-GoP, efficiency is gained from retaining the changes between frames, and when you have more frames per second to compress, it doesn't necessarily mean an increase in the bitrate because the changes from frame to frame are likely less, than the would be in the slower-fps version. Meaning, in 24p, each frame is taken every 1/24th of a second, and there's more time distance between frames than there would be in 30p, where each frame occurs each 1/30 of a second. More time distance means a higher likelihood that more will have changed between frames, which means each individual frame is harder to compress (and takes up more space) in 24p, than they would in 30p. So the net result is, generally, the bitrates are comparable in a long-GoP regardless of frame rate. 60p makes a difference, but in AVCHD they only bump the bittate up from 24mbps (for 24p/30p) up to 28mbps for 60p. Even doubling the frame rate only results in a relatively small increase in the overall bitrate.

But in ALL-I, it's possible that each frame is taking up the same amount of compression as every other frame does, and therefore faster frame rates would mean more bandwidth necessary, and slower frame rates mean less space will be taken up. As an example, let's take the HVX200 and DVCPRO-HD 720p. It's a codec rated at 100mbps, and if you shoot 720/60p, it will indeed take up 100 megabits per second. But, if you shot 720/30p, then it only takes up 50 megabits per second. And if you shoot 720/24p, then it only takes up 40 megabits per second. The way it works in DVCPRO-HD 720p is that every frame takes up 1.67 megabits, no matter what. So if you shoot 10 frames per second, it takes up 16.7 megabits. If you shoot 20 frames per second, it's 33.4 megabits. If you shoot 30 frames per second, it's 50 megabits, etc.

Is that what's happening in the GH4? I don't know, but I could see the case being made. It may only be 200 megabits per second if you're shooting at 60p. Assuming you were shooting 24p, in "200mbps ALL-I" mode, if it uses a fixed data rate of 200mbps for 60p, then that would equate to 80mbps for 24p, and 100mbps for 30p.

The GH4 doesn't have 4K/60p, but you should try recording files of 4K/30p vs. 4K/24p. If the 4K/30p comes out to 100mbps, and the 4K/24p recording of the same subject matter and the same duration comes out to 80mbps, then I think you'll have your answer.
 
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Hi

Cole said:
Bump on this.

I just ran some tests to prep for a shoot tomorrow and I am having the same issue. I am shooting 1080 (at clients request) 30p in .mov and wanted to use the FHD 200M option to give them the most data. I just ran my own comparison and here is what I see.

FHD 200M/All-I Actual result=82Mbps
FHD 100M Actual result=93Mbps
FHD 50M Actual Result=49Mbps

From what I understand the bitrate fluctuates depending on what you are shooting. These were basic handheld pans around my yard for about 20 seconds each. How is it that the 200M is lower than the 100M setting?

Is there another option I am missing or does the All-I only give you those bitrates when the footage is really taxing? It still seems the 200M setting should have at least broken 100Mbps.

Any insight would be appreciated.

Cole
Click to expand...

What are you using to give you the M bits per second?

Long GOP takes advantage of a video buffer, so at easier to compress moments the buffer is filling up ready to burst a higher data-rate on a scene change, or change in complexity of footage. This often means programs that report bit-rate will take into account the higher rate from the video buffer, and if they only sample the footage at set periods to report bits per second, they don't always give a true picture.

Regards

Phil
 
I'm doing some tests at the minute trying to find the best low-light combination of settings for shooting 1080p, but during it I tried the 200mbps ALL-I codec and compression looked absolutely awful.

I've uploaded some uncompressed stills and a comparison image available here: https://mega.co.nz/#!pUtgDKLQ!XUjnYTQfmgIned3AyQNKQywjZFLTrxlw6Zew_wwkWu4

. Every setting was the same except the codec. I'm pushing the camera to it's low-light limit so this was shot at 3200 iso in a deliberately very dark scene.

the bit-rate on the 200mbps all-i clip was 24.85mbps and the 100mbps IPB was 68.45mbps

The difference is astonishing (every frame in each clip was comparable to these, it's not a glitch)
 
When I shoot FHD 200M/All-I 60fps v2.0 firmware on a high motion scene I get 197 Mbps using quicktime movie inspector.
 
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Phil_D said:
What are you using to give you the M bits per second?
Click to expand...
I am going by what I see in the properties on windows explorer. I used to use Stream Parser for my GH2 footage but it isn't recognizing any of the GH4 files I have tried. It may not be entirely accurate, but I vaguely remember comparing the Stream Parser number to what I saw on the explorer window and they were very close. One correction to my original post though, they must have been MP4 files, not Quicktime. The Quicktime files I shot yesterday don't have any information in explorer.

I am going to do more tests at different frame rates and quality settings and see what I get. I was able to use a friends Ninja Blade and did a few tests. I will report those results as well once i take a look at them.
 
Cole said:
I am going by what I see in the properties on windows explorer. I used to use Stream Parser for my GH2 footage but it isn't recognizing any of the GH4 files I have tried. It may not be entirely accurate, but I vaguely remember comparing the Stream Parser number to what I saw on the explorer window and they were very close. One correction to my original post though, they must have been MP4 files, not Quicktime. The Quicktime files I shot yesterday don't have any information in explorer.

I am going to do more tests at different frame rates and quality settings and see what I get. I was able to use a friends Ninja Blade and did a few tests. I will report those results as well once i take a look at them.
Click to expand...

Open the files in quicktime player and press either Ctrl+I or Apple+I (if you're windows or mac) you can open MP4 and MOV in quicktime. It'll open the inspector window which shows you the bit-rate of the clip amongst other useful stuff.
 
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