@Butt Make films! Driftwood Productions. I bought two GH2's (instead of going for an AF101) to B cam alongside my EX3s and 5DmkIIs, etc... With this hack, I'm just trying to understand the mechanics to get the best out of the equipment and I'm sorry if I don't understand the deeper in/outs of the engine. I just want to learn like everyone else! And help. Gonna donate some more dosh to Vitaly now. I can't believe the amount of work he has to process. And with the help of some incredible guys around him. Really pleased with what some of you experienced guys have achieved so far. Sometimes I feel he would be better telling us 'drones' what to do to help - I have no problem with that. You pros can then analyse the results. :-)

We made some progress with Chris discussing all this stuff.
Also it seeems like we found the bug causing strange bitrate behaviour sometimes.

Chris will make few things and test them so we'll understand it even better.

We're working away at it. I've been looking at quantization scaling matrices, etc... There's still some more work to do. It will take a while longer. Hopefully, some good stuff comes out at the end...

I'm pretty familiar with the TI offerings. We've been looking at several codec's as background information. The Panasonic codec is pretty different, so it's a bit of a challange.

Chris

Wow.. nice offer. But I don't think it will come down to that. There are, however, lots of tests that will need to be run, so you'll be the first to know when the time comes.

Thanks!

Chris

Yes, I've read the standard. Gh2 uses 4x4 matrices only (as far as I can tell), which is legal

Chris

@cbrandin No, GH2 is using 4x4 AND 8X8's depending on the parameters. Look >
edit: ok, these are scaling matrix!

edit: ignore the first 24mbps wrong upload! Plus all the first picture frame sets start off the same in the first second, 6 4x4 and two 8x8, then as pfs change patterns seem to emerge from different bitrates.

edit: I noted all the first 6 matrices [0-5] were similar 4x4 tables of equal values, table matrix 6 was either =2 or =0 and matrix 7 (the 8th and last matrix) was mainly =54 or =0

I guess I was a little unclear. There are no 8x8 matrices in the firmware. If they are using them they are default matrices, which means we have no control over them. Vitaliy has published the IDA dis-assemblies of the GH1 firmware, which is fairly similar to the GH2 firmware when it comes to quantization matrices. Download it and IDA Free and look at the code - if you can point me to any 8x8 matrices I'm all eyes.

Chris

As far as I can tell, the GH cameras rely entirely on these pre-calculated matrices, which are all 4x4. There are a bunch of them; for each resolution mode there are four sets of six:

I frame Y-intra/Y-inter Cb-intra/Cb-inter Cr-intra/Cr-inter
B frame: " " " " " "
P frame " " " " " "
Special " " " " " "

My best guess about the "special" matrix is that it is used as a fallback when bandwidth runs out.

There are several sets of these: 1080p, 1080i, 720p high, 720p mid, 720p low. 720p low isn't used and 720p high and 720p mid are identical, so I don't know why they were built as separate tables - one would have sufficed. Actually, this is a good thing because we might be able to use the 720p low settings space for custom tables. The 1080p, 1080i, and 720p tables are all different. The 1080 and the 720 tables are entirely different; the 1080i tables differ from the 1080p tables in that the vertical values in the 1080i tables are adjusted to account for 1/2 the number of vertical pixels, otherwise they are the same.

By the way the best book on H.264 I've found is the one written by Iain Richardson. The second edition came out. It's kind of expensive, but worth it if you really want to get into this stuff. The standard - like all standards - is virtually unreadable, and the various papers published on the web typically over simplify things.

Chris

I looked at the 8x8 matrices in your printout. Have you noticed that they contain strange entries? They contain zeros, and the patterns make no sense - I've never seen tables like these, they seem to contain nonsense. They certainly aren't the default tables, or even close. The 4x4 tables I do recognize - they are straight out of the GH2 internal matrices.

Chris

@cbrandin sure. btw I just posted my findings regarding buffer sizes at initial startup of recordings. see stable settings thread

@cbrandin something definitely is going on with those unusual 8x8s. Because the data is changing as I look at each slice - not all the time, but they definitely differ when something 'changes' in the picture. I'll conduct test on my moving tests later tonight to confirm.

BTW: 'Special' frames are normally used as follows;-
"Depending upon on the subset of coding tools used, a slice can be of I (Intra), P (Predicted), B (Bi-predicted), SP (Switching P) or SI (Switching I) type. A picture may contain different slice types, and pictures come in two basic types – reference and non-reference pictures. Reference pictures can be used as references for interframe prediction during the decoding of later pictures (in bitstream order) and non-reference pictures cannot. (It is noteworthy that, unlike in prior standards, pictures that use bi-prediction can be used as references just like pictures coded using I or P slices.) In the next section we describe the coding tools used for these different slice types."

I quite like your theory that they are employed twhen the bandwidth adjusts but I'm not 100% that's correct.

@cbrandin What you asked for. Here's a comparitive dump of the I,B P frames at beginning to middle of recording on a GOP3 KAe recording. Ill do a 24mps Stock copmparison soon.