40 Mpbs Codec Breakdown

Neighborhood Studios

Neighborhood Studios

Active member
I have a question for anyone who may have experienced this codec issue before. I was filming a wedding, and at times the codec would break down, becoming pixelated and muddy, but then would recover after a few seconds. I noticed this issue during the ceremony, after having a static shot for a while and quickly panning to grab another angle, which would cause a breakdown in the codec. Furthermore, this issue occurred during the reception particularly during camera flashes. The flash would make the footage break down, and it would gain resolution and detail directly afterwards. However, this only seemed to be an issue during the dancing when house lights were dimmed. The images attached show the issue with great detail, but I have a video example as well. The first flash creates the effect best.
http://vimeo.com/26283571

I was running the 40 Mpbs hack with a Sandisk Extreme Class 10 card, ISO 800, shutter 1/60. I'm wondering if increasing the bitrate would aid in this problem, perhaps to the 75Mpbs hack. Or, maybe it's just an issue with underexposed images? Whenever the breakdown occurred, the video was slightly underexposed as a whole. I'm guessing that the variable bitrate drops down significantly when the image doesn't change or is darker, then tries to jump up when the camera moves rapidly or exposure shifts significantly. Is there a way to prevent the codec from dropping? Thanks!
Sequence 01.Still009.jpgSequence 01.Still010.jpg
 
What mode where you shooting in??(Creative Movie mode-manual? P/S/A/M??)
The video on vimeo was only 1280/720-30P-so was it edited??
Also, which video mode(FHD/SH/MJPEG) where you using??
I've seen this before, on some of my video's-usually indoors, with various patches. Still not sure what causes it.
 
I shot in Creative Movie Mode, at 720P60, using the AVCHD codec at SH quality. The Vimeo clip isn't edited, I sent a clip straight from Premiere to Media Encoder and put it online. I could put the original .mts clip up as well if that might help.
 
Neighborhood Studios said:
I shot in Creative Movie Mode, at 720P60, using the AVCHD codec at SH quality. The Vimeo clip isn't edited, I sent a clip straight from Premiere to Media Encoder and put it online. I could put the original .mts clip up as well if that might help.
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I think the problem may lie with your shutter speed. you should set it to 2x the frame rate, which on the gh1 is 1/125. i notice exactly the same thing in sh mode, at 1/60th-it's easily reproducible at that shutter speed.

as far as i know, there is no fix in post processing-short of removing the one or two pieces where it goes haywire.
i've also seen this happen if you're using auto-focus, the camera is a little out of focus, and hit half press the shutter button-for some reason, it induces this same "mud" that you're seeing.
I would wait for some of the experts to show up to tell you more-but I think you need to use 1/125. try filming indoors at both shutter speeds, 1/60 and 1/125 and see if you can reproduce the problem.
as far as the flash, i don't know if that caused the start of the problem, or not. it seems to be exposure related....??
 
havasuphoto said:
I think the problem may lie with your shutter speed. you should set it to 2x the frame rate, which on the gh1 is 1/125.
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Only if you're using the footage for slow-mo. If you're using it for the "live" 60p look, then the shutter should still be 1/60th.

In any case, using 1/125 should make the codec more likely to degrade, than less likely. In 1/60th, movement is a little more blurred, so there's less hard detail in the scene, and easier on the codec. Using a shorter shutter speed masks the motion blur and makes it more likely that the codec might choke.

It's been a long while since I've used the GH1/hack, but -- wasn't there separate settings for FHD mode, vs. SH mode? Don't you have to set different parameters? Maybe you had hacked the FHD mode, but not the SH mode?

And yes, a flash would be extremely likely to cause this kind of degradation, especially in an unhacked GH1.
 
thanks for that-obviously I was a bit confused on the shutter speed vs. codec stress thing.
the settings in the hack apply to both fhd/sh together. the next setting you can change is the H setting.

I've been having some crashing issues with SH mode, with all the hacks-and I have the sandisk III 30mb/sec card-so, I think Barry just discovered why I may be getting a write error, while others or not-shutter speed is to fast!!! Doh!!!
I had re-edited the 75meg lpowell patch , with the H mode set to 30xxxxx-it's still 720/60P, it just drops the bit rate, and I found it most stable at that setting, at 1/125(intending to do slow motion).
the hacks effect all modes......but, you can edit 720P mode separately from 1024 mode.

so, 2x the frame rate=180 degree shutter, and 1x=360???
sorry, been a long time......

and, if I intend on doing slow-motion, and went to say 1/500th, would that stress the codec even more??
there has to be a "happy medium" in regards to shutter speed for slow-motion. I only intend to slow it down to 24 frames per second(that's about 60%? slower). the "subjects" will be moving at around 70+mph.....(yea, I know-good luck with that.....)
 
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Be completely sure your shutter speed doesn't accidentally go below your frame rate or the codec will degrade immediately to below 9Mbps (instant mud). It's easy to make a mistake with the thumb wheel if you are adjusting exposure while in s or m mode in creative movie mode and forget to click it.
 
If you're trying to emulate a film camera's slow-mo look, then use 1/125 with 60p.

Only thing I was bringing up is, the crisper the shutter, the more resolved detail per frame, and the more that will stress the codec. Not that that's necessarily a bad thing, but if you think that going from 1/60 to 1/125 will make it easier on the codec, I don't think that'd be accurate, I think using 1/125 will make it harder on the codec.
 
It's really difficult indoors (like in your Church shot above) to keep the data rate high in sh mode with the 40Mbps hack. The low light and 60p framerate work against you.  I shoot mjpeg in this situation unless slowmo is a priority. <br><br>I shot a wedding two weeks ago in SH mode 720p50fps and 1/50 shutter, all slowed to .5 in post. It gives a bit more motion blur which i like for weddings as there is usually little motion going on. Keep the camera steady though.

Just watched your vimeo footage, that sure looks like a classic case of shutter lower than framerate, i have seen the exact same thing when i've set shutter too low by mistake. Check that clip for biterate, i bet it's well below 9Mbps.
 
havasuphoto said:
...I think Barry just discovered why I may be getting a write error, while others or not-shutter speed is to fast!!! Doh!!!
I had re-edited the 75meg lpowell patch , with the H mode set to 30xxxxx-it's still 720/60P, it just drops the bit rate, and I found it most stable at that setting, at 1/125(intending to do slow motion).
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Sharply focused, high-detail foliage in broad daylight is definitely the acid test for high-bitrate patches. And as Barry explained, shooting at 1/125 shutter will produce significantly less motion blur than at 1/60 or 1/50, and that can increase the bitrate. I've standardized my testing at 1/60 in NTSC mode and 1/50 in PAL, but I occasionally use 1/125 in sunlight and have noticed more failures at the higher shutter speed.

Unfortunately, I've found the NTSC 720p60 SH mode to have the narrowest safety margin of the four video modes that all share the single FHD/SH bitrate patch setting (1920p24, 1920p25, 1280p50, and 1280p60). 60fps is the highest frame rate the GH1 can sustain and it appears to stress the AVCHD codec a bit more than the modes with lower frame rates. Tuning the "H" setting as you've done to produce a lower bitrate for 720p60 mode is a good workaround.

The other technique I've found effective with brightly lit, high-contrast scenes in any video mode is to reduce exposure level by a half to a full stop. This can reduce the bitrate enough to complete the shot without crushing shadow details too far into black.
 
I sure was hoping that the hack would fix this issue as I have seen this with the unhacked GH1 too many times. I think that it is a limitation of the GH1 sensor. Is there a chance that you can test some 1080p 24fps footage at a low light event where the flash is being set off? I've used the GH2 at an event and it didn't appear to create the artifacts after a flash - if the hack doesn't improve the footage at 1080p I guess I'll have to trade up to the GH2.
 
Thanks all for the replies and suggestions. I really appreciate it. I've been trying to stress the camera at 1/60 shutter with camera flashes in a decently exposed room with no real breakdown.

I think rambooc1 hit the problem precisely with excessively low shutter speed. Premiere reveals the problematic clips averaging around 500 KB/sec. I also distinctly recall knocking the shutter down to 1/40 and even 1/30 at times, being frustrated with the lack of light at the wedding reception. I'll run some tests tomorrow to check on the low shutter speed and report back, but I bet that's the issue!

That would also explain why at times the ceremony footage broke down. It was an hour long clip, and I was swapping an f/2 and f/2.8 lens. Since I couldn't stop recording to change the ISO, I'm fairly confident I knocked the shutter down at times with the f/2.8 to bump exposure up again.

I sure was hoping that the hack would fix this issue as I have seen this with the unhacked GH1 too many times. I think that it is a limitation of the GH1 sensor. Is there a chance that you can test some 1080p 24fps footage at a low light event where the flash is being set off?
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I've stressed the codecs before at events, and they've always held up very well. Shutter speed was locked to 1/60 at the event linked below (720P, but still should hold true with 1080).

http://vimeo.com/25695145

Skip ahead to 1:55, the codec holds up under extreme conditions at 1/60 shutter. I'll bet it's a low shutter problem. Thanks so much, I'll run some tests at 720 and 1080 and post back!
 
Neighborhood Studios said:
I think rambooc1 hit the problem precisely with excessively low shutter speed. Premiere reveals the problematic clips averaging around 500 KB/sec. I also distinctly recall knocking the shutter down to 1/40 and even 1/30 at times, being frustrated with the lack of light at the wedding reception. I'll run some tests tomorrow to check on the low shutter speed and report back, but I bet that's the issue!
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Ask me how i know, i've done it on a number of jobs where i needed slowmo but the lighting conditions were to low for 50p and i adjusted the shutter below 1/50. I paid the price with extremely low bitrate footage. As i said i now switch to mjpeg at 30fps and 1/30.

Yes it works fine on your HMC 150 because it is a different codec.
 
As i said i now switch to mjpeg at 30fps and 1/30.
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Excellent, thanks again for the tip. Now, isn't there a limit to recording time at mjpeg? At least the time counter isn't reliable? There are times during the ceremony that having such a shutter speed would have helped exposure but I need to be recording continuously for an hour without fail or filling up my 16GB card.

I ran a test at 720P and successfully introduced the compression error.
http://vimeo.com/26361326

I haven't seen it in 1080 with the 40 Mpbs hack without true 24P checked, but I'll see how that, and other hacks affect the quality of footage.
 
Thanks Ryan for the test videos. I tried a low light test between the GH2 and the GH1(unhacked w/auto ISO on) with the shutter speeds at 1/30 than at 1/60 and I got the artifacts after the flash on the GH1 for both and good results from the GH2. Than I tried it with ISO at 1600 and 800 with shutter at 1/60 and I got better results with the GH1 at 1600 than at 800. AT 800 I got the Artifact but at 1600 there was little or none. Strange!?!

Just wondering if you thested any low light 1080P at your last event?
 
PixelWrangler said:
Thanks Ryan for the test videos. I tried a low light test between the GH2 and the GH1(unhacked w/auto ISO on) with the shutter speeds at 1/30 than at 1/60 and I got the artifacts after the flash on the GH1 for both and good results from the GH2. Than I tried it with ISO at 1600 and 800 with shutter at 1/60 and I got better results with the GH1 at 1600 than at 800. AT 800 I got the Artifact but at 1600 there was little or none. Strange!?!

Just wondering if you thested any low light 1080P at your last event?
Click to expand...

Very strange! I don't shoot 1080 at the events I shoot since I like the option of slow motion, but I did try the same test I posted previously, but this time using FHD 1080i (not 24p) at 50,40,and 30 for the shutter speed. I did not see any breakdown with light fluctuation at all, nothing even close to the breakdown at 30 shutter with 720P60. However, you did mention that your GH1 is not hacked, while mine is. That probably plays a significant role in why your footage is deteriorating so much. FHD 1080 seems to be immune to these artifacts from what I've seen.
 
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