AVCHD maximum image quality settings and testing

olegkalyan

I second that, really want to test 220 in best setting currently

proaudio4

Stray,
Tomorrow, I should be able to perfom the tests on 88M AQ2 (and AQ3) max variation.
Based on recent discovery from Ralph's HDMI comparison to the max variation 66M AQ2, were you able to get 88M AQ2 without the buffers set for max variation.
In other words, basically a stable version of 88M AQ2 set in the same manner as Chris's original 66M AQ2?
When I attempted this a couple weeks ago, I had cadence issues (veiwed on streamparser).

So far, based on Ralph's test, Chris's original (Aug 29th) 66M AQ2, appears to be the best reasonable bitrate setting. Of course, driftwoods 132M GOP3 is still king.

Stray

No, I havent managed (or tried again recently, tbh I can't really spend any time testing/patching the camera for a few days now) to get a stable 88M AQ2 in the same manner as Chris's original 66M AQ2. However, I think the key to doing this would be to dramatically pull down the framelimit setting, as driftwoods findings seem to suggest that an overly large framelimit setting is responsible for cadence issues. I've definitely seen doing so improve the stability. Also, my own instinct is that the high top/bottom low top/bottom also need to be cranked up a bit (like x4.8). I have absolutely no idea why now but certain results gave me the impression that doing so contributed to stability in the max variation version.

I reckon, (just by looking at the footage shot, and the bitrates its recording at), that the 66M max variation running at AQ3 is as good as the original 66M AQ2 in quality terms. I'd therefore think that (if it is as stable as it seems to be) that running this max variation 88M at AQ3 will be as good as a stable 88M AQ2 working in the original, less variable QP style.

proaudio4

OK, thanks Stray.
I'll post my findings.

driftwood

@daimon I ve been using fcp7/cinema tools to correct the frame reorder. But premiere pro 'interpret' works too. Had no probs with NeoScene too on the Mac. Playback wise, its great on the PC so long as you get a decent codec such as CoreCodec's CoreAVC(R) Professional Edition a superb H.264 Video Codec. Link: http://corecodec.com/products/coreavc

driftwood

@daimon Wait a bit, I hope to have a best short gop on all settings by end of tonight.

B3Guy

anybody got any solutions for reordering frames for FCPX?

daimon

@driftwood Perfect! Will wait for your new best settings.

sohus

I think it is a long night for @driftwood :)

driftwood

Already have great 3 gop in 720p just trying to get a decent 720p 1 gop.

proaudio4

driftwood,
Please point me to your 3 GOP 720P settings?

driftwood

Will do soon. Still refining 50p

daimon

@driftwood Let me know when you have new GOP1 set. Appreciate your work! Would also want to test your 25P you are working on.

_gl

Hi guys, I've read a few pages here, thanks a bunch for nailing these settings for the rest of us. I've been shooting with Chris' 44m AQ4 and pretty happy so far, so it's interesting to see how much more the higher bitrates actually buy you.

Just one comment after reading some of @Ralph_B 's HDMI tests (ignore if this is already old news, I don't have time to read all the pages):

Testing with very high shutter speeds to 'stress the codec' is dubious imo. 9.9 times out of 10, 24p footage is shot somewhere between 1/25 and 1/100 - you need some motion blur in low-framerate modes likes 24p or motion becomes unbearably strobey. OK so this strobing _can_ be useful if you want eg. Gladiator-style fight scenes, where it can simulate the disorientation of a real high-adrenaline event - but if 3x the bitrate is required just so the codec can hold onto completely unblurred motion then it's a waste for general shooting, and may also give misleading 'real-world' codec results.

Of course it's worth having settings suitable for different scenarios, just realise that high shutter speeds don't represent what people actually need most of the time, so testing motion rendering @ 1/25 - 1/100 is very important too. (edit: or just pick the popular ~180degree shutter 1/50).

proaudio4

@_gl
Well I certainly disgaree with 100% of what you just wrote. ;)

The camera should actually be able to record without failing using different settings on a camera, ISO, shutter speed. etc...
If a new unhacked GH2 failed for recording at any setting, this would be called defective. This is "real world".

Also, many do shoot at very high shutter speeds either due to:
1. They want the look.
2. They don't own an ND filter and want to maintain f-stop for DOF.
3. They shoot fast action sports

And most important why we are doing this is to find the best quality capable of running in the camera without failing.
Stray's last 88MB AQ2 MAX VARIATION (take-off from Chris's 66M MAX VARIATION version) passed my tests.
I'm in the process of posting this info now.

stoney

@_gl

Who said @Ralph_B is going to use high shutter speed for his own works? He stressed the codec by raising shutter speed to test reliability of the settings. We thank him for that.

_gl

@proaudio4, @stonebat, I wasn't talking about reliability, I was talking about comparing high-shutter _motion_ with HDMI for IQ. That's (most of the time) not a real-world case.

stoney

You are happy with the 44Mbps AQ4 by Chris, right?

_gl

@stonebat, I've only done one shoot with them & haven't edited that fully yet, so it's too early to say. But from what I've seen here so far, I think the sweet spot is a general purpose bitrate that gives nearly top quality at a reasonable file size (I guess 44AQ4 or 66AQ2-3). If that could span, even better.

Of course the more extreme settings will be useful too, but I personally wouldn't use them unless I really needed to as I don't see a huge gain.

stoney

Chris tested his 44Mbps setting with high shutter speed. You are getting benefit from his high reliability testing.

Many people transcode raw files to intermediate codec like ProRes and DNxHD to produce all intraframes. Easily over 100Mbps.

High bitrate setting was proven to give better original noise reproduction.

_gl

Let me clarify my point as you seem to be missing it:

You're trying to get the best possible image quality, that's great. But running the codec at (say) 1/2000 shutter speed is forcing it to dedicate huge amounts of bitrate to motion, as every frame is essentially unblurred and different. My point is that if you tune the codec for that scenario _for image quality_, it will not necessarily give you the best IQ for the more common case where motion is blurred. Or it may use more bitrate for motion than is necessary for the more common 'some motion blur' case.

So sure, find settings for both scenarios (and of course reliability is crucial too), just don't use high shutter speeds as the only way to measure codec motion IQ.

And transcoding is a separate issue - the point is the GH2 codec is not intra, yes you can tune it to work more like that (lower GOP etc) but not everybody needs or wants that. I personally need a balance between file size and quality. But of course I would like the best possible quality at that sweet spot.

stoney

With all due respect, you seem pointless. Nobody cares about your personal favorite setting at your sweet spot.

_gl

Whatever @stonebat, clearly not possible having an intelligent conversation with you.

proaudio4

@_gl
We're not here to talk about settings.
We are here to find the limitations of our settings to maximize image quality.

Please re-read my post. Again, the camera should not crash upon any setting the user chooses in the menu.
If the stock GH2 did this, not many would buy it.

Stray

@_gl
"I personally need a balance between file size and quality. But of course I would like the best possible quality at that sweet spot. "

We all are really. The results of running the camera at extremes, and the settings used to achieve those extremes, directly inform what settings we use to get the size/quality and motion rendering quality we personally want. In order to find the correlations between the settings to get what we want you need to be able to analyse a dataset thats as wide as possible. So, seeing peoples results at extreme settings, and reading peoples theories as to the results (hinting towards what this codec is actually doing) is the only way to get that personal sweet spot. I think in the end we will get to the point where we'll know exactly what settings we will need for the AQ, GOP and bitrate we want without having to run so many tests. I do think personally that giving the codec its head so to speak, as per the max variation approach of Chris, is the correct way forward. But discoveries could be made that completely change my opinion, and they will more than likely come out of some extreme test and/or bitrate.

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