@RBD I don't need to know the stuff to the degree that Vitaly or Driftwood know it. But when I'm reading he threads on the various patches, I'd like to have a clearer idea of what's going on. (Especially since the usual response to questions about patches is "read the forums.")

Take the issue of matrices. The impression I get is that the GH2 uses a table of values to facilitate rapid calculations of the incoming data stream-- rather than perform calculations over and over to, say, compress the data,, the camera simply consults this table. And, that people have created different tables that lend themselves to better image quality. Now, I could be wrong, and I'd like to know how I'm wrong.

Delete.

The author of this thread has been here more than twice as long as I have.

@Brian_Siano

One place to start is to go to the following folder and read the first few posts in each topic:

http://www.personal-view.com./talks/categories/hack-top-settings

That should give you a quick impression of the most popular patches. When you come across an unfamiliar term, like "intra-frame" or "GOP", just whip out Google, combine the unknown word with the term "H.264", and you'll likely find some helpful links. For example, Googling "GOP H.264" will lead you here:

http://en.wikipedia.org/wiki/Group_of_pictures

Maybe we ought to have a thread where we draft up and refine a good FAQ on the subject. Here's a first stab at it, and obviously, changes, amendations, and clarifications are needed.

1. The Basic Overview

When video is recorded, it is usually compressed; otherwise, it'd require writing massive amounts of data to the memory card, which may not be large enough or fast enough to handle it. This requires the camera to perform some very intensive processing to compress the data, so that it can be written to the memory card.

Because this processing takes place during shooting, the camera has to do this very quickly. So the camera relies on shortcuts, which will be described later in in this FAQ. As a result, the camera uses "lossy" data compression, and the image and motion quality can be compromised. (For now, we recommend reading Wikipedia on http://en.wikipedia.org/wiki/Video_coding#Video.)

Vitaly's hack enables users to reconfigure the way the camera encodes the video, in order to improve the quality of its recording images and motion.

This reconfiguration is complex, and sometimes, the settings may not work with each other. (For example, some patches with high image quality may have trouble recording acceptable sound, or "spanning" across multiple files. More about this below.)) So some users have spent a lot of time and effort experimenting with the settings, and they have developed "patches" with various strengths and weaknesses. These include the Sanity patch, the FlowMotion patch, and the many patches developed by Driftwood.)

New or less-techy users may find it daunting to read through Personal View's lengthy forum discussions, which can be very technical. This FAQ is intended to give such users a rough idea of what's going on.

1. Bit-Rate

(Need discussion here of what bit-rates mean in terms of video compression.)

1. Interframe and intraframe

These are two techniques by which video is compressed. The simpler technique is "intraframing." For each frame of video, the camera compresses it down in the same manner as a JPEG picture file. This can be very lossy, or even lossless, but it also requires a lot of processing work by the camera.

A more complicated method is "interframing." Here, the camera records an initial frame as a full photo. The camera then records the subsequent frames as only the changes that occur from the previous frame. (See http://en.wikipedia.org/wiki/Video_coding#Video) for a discussion.) So the video file may consist of the initial Frame 1, and then data that contains only changes between Frame 1 and 2, then between frame 2 and 3, etc.

Since most frames aren't stored as full frames, but are calculated, this technique requires the camera to make a lot of calculations before writing the data to the memory card. It is also a lossy technique. It can be made less lossy by sampling full frames more frequently.

3a. Refinements to interframe Not written yet: see http://en.wikipedia.org/wiki/Inter-frame#H.264_Inter_frame_prediction_improvements for now.

1. Matrices (Not written yet)

@dadix

"The Hidden Cost of H.264"

Irrelevant, unless you're concerned with the cost of network streaming H.264 video from a centralized server running on circa 2008 hardware.

As a very beginner here, this is all very helpful. And, I'm finding LPowell's "Flowmotion" to be a beautiful choice for long take free form wide-angel intimate documentary shooting, that I'm testing for at the moment. Thank you to everyone.

@Brian_Siano

You can just make page on wiki, don't thing that forum post, especiall unformatted is so great place.

What do you think?

Check

http://en.wikipedia.org/wiki/Markdown on formatting.

As for Wiki, register on wiki and tell me your nick on it.

Okay, I've posted a full First Draft of this FAQ over at my Wordpress site:

http://briansiano.com/?page_id=340

If it's accurate, then if anyone comes in asking for an explanation of how the hacks and patches work. you can point them here.

Great summary @Brian. @Vitaly could add it somewhere on top so newcomers with be informed before they start posting.

@Brian_Siano If you don't mind me spotting, I've seen a few "incorrections" :

"Earlier, we said that video could be stored as a series of full-resolution TIF files, but this would create far too much data. One way of compressing that data would be to store each frame not as a TIF file, but as a compressed JPEG. (As you may know, saving a TIF file as a JPEG makes a much smaller file.) This technique is called intraframing. " Intraframing isn't applying JPEG compression (as a matter of fact h.264 still compression is much more evolved than JPEG which is also used on MJPEG).

Intraframing as oposed to Interframing is encoding the frames independently of others frames. This is exclusively about exploring temporal redundancy, not about compression techniques.

"Every tenth frame will be a perfect, uncompressed frame—it’s called an I-frame (for “initial”). Your camera uses motion prediction to “predict” what the fourth and seventh frames will be from that I-frame. The fourth and seventh frames are called P-frames (for “predicted”) And the frames in between the P-frames—the B-frames, for “bi-directional”) are, in turn, “predicted” from the surrounding P-frames."

I-frames are indeed compressed. What you meant to say is that they are independent. I'm not sure on the GH2 implementation but it's possible for h.264 implementations where B-frames can be referenced to build other B-frames, thus invalidating that last sentence.

"The GOP Size is the number of frames between each P-frame. In our example above, that value would be 4.The GOP Length is the number of frames in the group—or the number of frames between I-frames. In our example, this value would be 10."

On GOP Size/Length: your definition is correct but from what I've seen around here (and pttools isn't conforming to that definition either) there is a misconception and it seems like both terms are used for the distance between two consecutive I-frames, which isn't correct. I suggest you remove the GOP Size reference or put most of the emphasis on GOP Length or re-educate the whole community. :)

"This does not always work. You can’t simply use Vitaly’s hack to specify a 100 mbps bit rate and the camera to work flawlessly. Your memory card may not be fast enough or large enough to handle a flood of uncompressed data." It's a large flow all right but all data that reaches the SD card is already compressed.

Gotta do some work now. Thanks for putting this up.