Ok so now that GOP has its own 'Don't Cry For Me Argentina' thread. Can someone start it off by explaining in simple terms the principles and real/or perceived benefits? ;-)

The Cliff notes for GOP:

If you don't increase bit rate you shouldn't decrease the time for GOP. Basically if you decrease the time for GOP then you cut down on its efficiency. Sure it can make each frame look better but only if bit rate is raised significantly.

Think of the video as a wave. You want the biggest ridable wave possible. You can decrease the time between waves and make it more likely to catch a good one. However, when you decrease the time between waves you also make them smaller.

You can also put a big storm near where you are and pump gigantic waves into your area with really short time in between the waves. You are almost guaranteed to see GIGANTIC waves that may or may not be ridable depending on a lot of other factors. You are also very likely to kill yourself/camera/videos.

Bottom line: Don't be an idiot hot shot who gets himself killed on the first wave out. Just sit back and relax. Let the locals show you where the waves are breaking. Then after you have studied enough you can jump in the line and show your stuff.

For people who have been making films with actual film for a couple decades (and I am in this category) I think we just became used to a certain look when filming motion. Since each frame of a 24fps film is a separate complete image that is not approximated from anything either coming before or coming after, filmed motion has a unique look. A lot of people don't like the look and find it choppy so they love 60p that takes all the choppiness out of it. Just a matter of preference. Shooting motion with a lower GOP on the GH2 for me at least looks better with a GOP setting of 3 (2 or 1 would be better at a 100mb data rate but it doesn't work) and thanks to the new GH2 chipset and Vitaliy a 24p 3 GOP actually lays down quite nicely. Technically, I guess the image quality suffers when doing this but I would argue it doesn't suffer at all when filming motion, it looks better. You see a lot of GH2 vimeos where the camera slowly plans or rack focuses to something pretty and static in the background. This footage is impressive and perfect for vimeo but has nothing to do with 'movies' or 'motion pictures'. They don't call them 'stillies' or 'static pictures' the word 'move' or 'motion' is in there for a reason. Hence I think there's some merit in shorter GOP stalin hack research if the shorter GOP lengths lead to better motion capture.

@mpgxsvcd
"Sorry man but I have been reading your posts and I call BS. You can't tell the difference between 1/30th shutter speed and 1/50th shutter speed and you can't see a more "Film-Look" with different GOP values."

What? Are you serious? A 1/30 (or 1/24 with 24p) shutter is what we cinematographers refer to as an OPEN SHUTTER. It means that the shutter stays completely open between exposures and leads to a smeary, and what people refer to as "video", look. I can MOST CERTAINLY tell the difference between 1/30 and 1/50 shutter speeds. It sticks out like a sore thumb to me... if you cannot, then you shouldn't be doing your own DP work. Sorry, but this is elementary cinema 101. I don't think you're in any position to call me out on what I not capable of noticing. Having an eye for shutter speeds and motion is what sets the "cinematographers" apart from the "videographers".

@mpgxsvcd

"and I call BS"

That's some pretty rank commentary. I think we've all been saying it's subjective. I totally believe you can't tell the difference between a 1/30 or a 1/50 or different GOPs but please allow that others might.

@hsitz

Again, I'm not the best at explaining the technical details... I'm just trying to express the visual differences I see. Obviously, the frames get re-constructed, but the motion doesn't... some parts of the image (most noticeably backgrounds) remain VISUALLY static, I don't care what data is doing what. GOP motion does not look like film motion. End of story. If you have never shot, edited, or worked with film, then you are in no position to tell us otherwise. Like I said, MOST PEOPLE DO NOT NOTICE... if you are not a film-junkie or cinematographer please stop calling me, and the others, out.

For those of you who ARE interested in achieving the most realistic film-motion possible... here is some reading on the 180 degree shutter rule. http://blog.tylerginter.com/?p=385

Yes, main reason was that in GH1 encoder we could't make bitrate go higher other way in medium or low detailed scenes.

". GOP motion does not look like film motion. End of story. If you have never shot, edited, or worked with film, then you are in no position to tell us otherwise. "

Look here, e.g., for a scheme where GOP compression is done LOSSLESSLY: http://www.ece.ubc.ca/~rafeef/papers/ICASSP2008.pdf

What that means is that every frame in the reconstructed GOP-compressed recording is IDENTICAL to the full original frame. If you play back such a recording every frame is the same as the original would have been in a lossless recording that fully recorded each individual frame. So long as the frames are played back at the same speed it is impossible to tell a difference, yet it is unquestionably "GOP motion".

Whatever you're seeing (if you are seeing anything objective) is nothing inherent to long- GOP-compressed recordings. Maybe you're seeing something that you're calling "GOP motion" that is unrelated to the GOP compression. Or maybe some blind testing where you have no ideas which recordings are long GOP and which are short would be enlightening. . .

@hsitz

We're arguing about two different things. You're talking about "data" being re-constructed and I'm talking about the rendering of motion... it's not the same.

@Vitaliy

What!? I'm just defending myself, and others, from people who are coming in here and telling us that we are crazy for wanting a lower-GOP. If people disagree with that, why are they even clicking on this thread? I never started the flaming. The guy who said "Sorry man but I have been reading your posts and I call BS. You can't tell the difference between 1/30th shutter speed and 1/50th shutter speed and you can't see a more "Film-Look" with different GOP values." is the one flaming.

People came here bashing my subjective opinion, and I'm trying to defend it from a onslaught of ignorance claiming that "you can't tell the difference between 1/30 and 1/50 shutter". It's insulting to me, from a DP perspective, just like my technical explanations (that I get wrong) are insulting to you as engineers.

And yes, when I finish my low-GOP films... I'll post the links here first. I'll be shooting one Wednesday night, you can all watch it this weekend.

Guys, will someone here just try my 3 GOP setting with the new hack to a) See if it handles motion any better for you than at 12 gop and b) if there's any way to help me get better quality out of it. I'd appreciate any help cuz I'm still not clear on what a lot of the new settings do and the first couple frames do glitch.

@kae

I'm trying to load the setting but I can't figure out how to... Is it not possible with Winebottler on OSX or something?

kae asked: "why the heck do you think lpowell devloped his 3-frame GOP fast action patch?"

Two reasons, both technical rather than subjective:

1. I developed the Fast Action 3-Frame GOP Patch specifically to optimize the 30p SH video mode on the GF1 (and also on the G2 and GH1). However, when I cut the frame rate of the SH 720p60 mode down to 30p, the average bitrate dropped as well. Reducing the GOP-size of a video stream will pack more key frames into each second of video, which in this case was useful for raising the bitrate back up to the level I was aiming for. I then tested the patch to determine the shortest reliable GOP-size and discovered that 3-frames was the sweet spot.

2. At 30fps, a 3-frame GOP produces 10 key frames per second. At this rate, each GOP only has to handle the amount of motion that occurs in 1/10th of a second (compared to the 1/2-second GOP-length of the stock SH video mode). Since only short motions can occur within each 3-frame GOP, the two P-frames can be efficiently encoded with motion vectors that use a minimal amount of bitrate. With the boosted bitrate of the patch, the encoder has enough bitrate to accurately track very quick motions without smearing the details. Hence, the Fast Action 3-Frame GOP Patch.

While a one-frame GOP (i.e. all key frames) can potentially track even quicker motions, the loss of efficiently compressed P-frames would more than double its required bitrate. A one-frame GOP that ran at the 55Mbps maximum bitrate of the 3-frame GOP Patch would suffer from a significantly lower static image quality.