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GH4 bitrate - I can't see the difference


markbatey

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Hiya,

 

First post here, been lurking for a while, so here goes...

 

My GH4 arrived yesterday, and I'm having lots of fun playing with it. I'll probably be shooting mostly in HD as my old laptop won't handle 4k at all. So I thought I'd do a test with the different bitrate options in HD - pointed the camera on a 60mm lens at leaves swaying in the breeze, and tried it at 50, 100 and 200 Mbps. And I can see absolutely no difference in the pictures. 

 

Is it just me? Sharpness is the same, motion blur is the same, freeze frames on moving leaves is the same. 

 

Can anyone else actually tell the difference? And what should I be looking for? 

 

Cheers

 

Mark

 

 

 

 

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Guest Ebrahim Saadawi

Same here. Did severe exposure pulling around, severe coloring, and they look identical, and fall apart at the exact same points.

It's not just 200 vs. 100. I am talking about 50. Here.

Tells you a lot about how the efficiency of the codec is MUCH more important than the compression value numbers on the spec-sheet. And It's a pretty efficient codec on the GH4.

I ended up with the conclusion that 4K is the best option really and using 1080p on that camera is kind of a waste as it isn't much different from the GH3 for example.

If your computer is not fast enough, you can take all the 4K footage, transcode it to 1080p ProsRes or DNxHD 4:4:4 10bit using free software like Mpeg Streamclip. And then edit from those.

The files will have are much higher quality than internally captured 1080p, as well as much lighter on your computer in terms of editing speed (ProRes & DNxHD are much easier, faster to edit than internal H.264 for slow computers)

If you don't want that extra intermediate step, shooting 1080p at 50mbits seems fine. But it is worth the extra step to get alias-free 4:4:4 supersampled 1080p!

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Yeah, I don't even have the Gh4 yet, but shooting 4K, backup/archiving the raw files, and then transcoding it into 1080 will be my standard workflow for most stuff.

 

Other times, for larger long form documentary work, I'll probably do low-res proxy editing and then re-connect only the large res clips that make it into the final cut.  (it's like it's 1993 all over again!  That's how AVID used to handle "hi-res" 640x480 stuff back in the day)

 

Or not...might get a new computer this year too so we'll see how it goes.

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Guest Ebrahim Saadawi

Yes as "fuzzynormal" said, that didn't come to my mind but is a very viable alternative workflow for slow computers.

If you, OP, can handle a proxy-editing workflow (as in making lower quality versions of you files for fast editing, and exchanging them with the original files before final redering), you can do that. And that way you gain the extra advantage of reframing and cropping in post that 4K provides.

So two options for slow computers to work with 4K:

1-Proxy editing.

Disadvantages:
-Takes time to make the low-version files before working.
-A bit too much and cumbersome to handle the files for some.

Advantages:
-Much higher IQ than shooting internal 1080p
-You get all the benefits of 4K, full sensor readout (No aliasing and moire), higher detail, deeper bit depth and color fidelitiy (4:4:4 8-10bit)
+including cropping and reframing in postproduction.

2-Transcoding to ProRes or DNxHD 1080p

Disadvantages:
-Takes time to make the 1080p ProsRes/DNxHD files before editing.
-You lose the ability of cropping and reframing in post

Advantages:
-Much higher quality than shooting internal 1080p.
-Easier more direct to work with than with proxy files.
-You get all the benefits of 4K as in higher resolution, no aliasing/moire, better colors, etc (just without the crop/reframing ability)

Choose your posion based on how important crop-ability is for you, if it isn't, just go with option 2. Make high quality uncompressed 1080p files and just work from there.

Just don't do internal 1080p. It really is bad compared to 4K, amd if you care about image quality at all you shouldn't touch that mode. If you don't care about the 4K higher quality, you shouldn't have paid the premium for the 4K capability over the Gh3!

Welcome to the forum and good luck.

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I too have a quite slow computer for 4K, but I do it slightly different to great  success so far: I have put in a SSD disk for previews. I set up Premiere with this disk for previews and import all my 4K clips into the timeline, join them together (no edit just yet) and render the whole timeline (into that SSD) so it goes green.

THEN I edit with blazing speed. It's worth noting that I only use the fast color corrector and similar native PP correction tools that don't require re-rendering.

When the edit is done I make adjustment layers and grade to taste. At this point the timeline turns red again and  will have to render yet again to stop lag/stutters, but this workflow works very well for me at that computer.

Until I started doing it like this, editing was a painful process, especially now with the GH4.

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Shoot 1080/60P with shutter speed 1/1000s and track fast moving sports. I think you then see some minor macroblocking in 50mbs ipb vs 100mbs. 

 

If you cant see the difference then GH4 codec is very good. My GH3 shows few artefacts with 50mbs.

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1-Proxy editing.

Disadvantages:
-Takes time to make the low-version files before working.
-A bit too much and cumbersome to handle the files for some.

 

Proxy is a pain for shorter form edits.  When one's doing long documentaries and the footage to edit ratio is something like 400:1, it starts to make a lot of sense however --as the log and transfer stage can also be a step to cull the footage.

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That's all really useful, thanks. I'll try proxy first I think and see how my late 2011 Macbook handles 4k that way - if it's still slow then it looks like transcode to ProRes 1080 is the way forward as I know I can work that way with no problems in the edit. 

 

Or spend even more money and go for the MacPro - the way it handles 4k in FCPX, even with multiple filters applied is just amazing. Then it's thunderbolt raids and all that fun... 

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I've been doing my late 2011 macbook a disservice. I've been trying it out, putting 4k material into an HD project in FCPX. It runs ProRes transcoded media even at "better quality" with no bother at all. With proxy obviously it doesn't break sweat and it'll handle multiple streams as well so dissolves play back smoothly. The only drawback might be disk space - the transcoded files are four times the size of HD. But if I find that's an issue I can work with proxy where the files are very small.

 

All media running from a G-raid 4TB over firewire. 

 

And FCPX makes the whole workflow really easy. 

 

4k it is then from now on!

 

I've got another question about whether this can be a broadcast-compliant camera without an external recorder, but that's probably for a different topic...

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Guest Ebrahim Saadawi

Broadcast-approval in the UK by the EBU requires a minimum of 50mbit/s and 4:2:2 chroma subsampling. Since the GH4 doesn't do 4:2:2 internally, it's probably not.

They do individual tests of cameras though, and It will be interesting to see if the EBU will consider the 4K 4:2:0 to be equivalent to 1080p 4:4:4 and thus approved for 1080p acqusition or not. They should. And I believe the internal 4K on this camera is way more than enough for the highest of broadcast work. That image is not any worse than the 4:2:2 1080p out of the C300, which is the king of broadcast right now.

But as I know their mentality, I think they'll just dismiss the 4k as 4:2:0 and require externally recorded 4:2:2.

All that is only relevant for UK broadcast though. All otger broadcasters in the world will take your internally recorded 4K happily!

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It isn't an image quality thing...

 

The different 1080p modes vary in other ways.

 

ALL-I for instance is easier on your computer to edit. The complex encoding for IPB is not there, just each individual frame 'as-is' one after the other like a sequence of JPEGs.

 

The bitrate of 200Mbit/s is higher in ALL-I just to maintain image quality, not to improve it from 100Mbit/s in IPB mode.

 

Because the efficiency of an ALL-I codec is lower, the data rate needs to increase.

 

So it is a common user misconception that image quality and bitrate have a direct correlation!

 

Shoot 1080p ALL-I if you need easier to edit files.

 

Shoot 1080p IPB if you need smaller file sizes and best quality compression.

 

Shoot 4K and upgrade your laptop if you want to get a clue ;)

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Could some one tell us / me what are the actual bitrates the GH4 records in the different recording modes ..

The menu option it self tells us pretty little if the actual recording bitrate in 200 Mbit mode is just 50 like some ppl are reporting on the web.  

 

4K = 

1080p 200 average , max =

1080p 100 = average , max = 

1080p   50 = average, max =

 

Would be higly appriciated. 

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If your computer is not fast enough, you can take all the 4K footage, transcode it to 1080p ProsRes or DNxHD 4:4:4 10bit using free software like Mpeg Streamclip. And then edit from those.

 

Can someone PLEASE tell me the best way to convert the GH4's 4K footage to 1080p ProRes? And is it really possible to get it to 4:4:4 ProRes? Even 10-bit?

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Guest Ebrahim Saadawi

Can someone PLEASE tell me the best way to convert the GH4's 4K footage to 1080p ProRes? And is it really possible to get it to 4:4:4 ProRes? Even 10-bit?

Mpeg streamclip. Free. Google it it's an awesome transcoding app. If you can't find Apples Prores in the export options (if you're on PC) You can download the Avid Codec pack from Avid website, then the Avid DNxHD codec will appear in Mpeg streamclip, DNxHD has a 1080p 4:4:4 10bit codec, very similar to ProRes HQ in quality and file sizes, but works with both mac and pc.

And yes, you so really get 4:4:4 chroma subsampling. And perfect 1080p detail. It's quite fascinating really. The 10 bit part, I am researching that right now. Will let you know!
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