Official Low GOP topic

AK2

I made a short in Austria. I actually wanted to make something different than just a view shots. I`m very impressed by the quality!

Setted the firmware to:
Bitrate in 24H to 50000000
AVCHD GOP Length at 1080i and 1080p24 GOP Size to 3

pingpongcomputer

GOP length of 50 million? 1 I frame per 578 hours of footage?

AK2

@pingpongcomputer sorry it was to late yesterday evening i set the GOP length to 3 of course.

cosimo_bullo

GOP 1 is a revelation! Now seems to leave mjpeg in the dust grainwise, and for what it's worth, we've yet to have any crashes this evening even shooting detailed scenes at 2500iso. We'll try to do a detailed vs. test tomorrow.

cosimo_bullo

Clipwrap however is chocking in the files and creating a strange on output not matter if we rewrap or convert to prores. - however Final Cut Pro 7.0.3 was able to ingest the files fine and they play back correctly.

Oedipax

Exciting stuff, thanks for the updates @cosimo_bullo. Gonna be a long wait for this weekend when I can try the new PTool out.

Vitaliy_Kiselev

I know that this is low GOP topic.
But you can now also try double GOP.
I mean 24 instead of 12, etc. And PTool also will recalculate things inside.
Hints for GOP patches have all supported values listed.

danyyyel

@cosimo_bullo So you are able to have stable and high bit rate (how much) 1 gop recording with the ptool 3.62 ??? So if this is the case, Vitaliy has invented the first intraframe avchd codec :-)

LPowell

@danyyyel You might find this article on AVC-Intra of interest. Both it and AVCHD are members of the family of H.264 encoders:

http://en.wikipedia.org/wiki/AVC-Intra

No_SuRReNDeR

AVC-Ultra looks dope...4:4:4 12bit = epic win.

ishvar

GOP stuff - but the diehards will prob. already know this, but still.....
http://www.google.nl/search?rlz=1C1CHMR_nlNL339NL343&sourceid=chrome&ie=UTF-8&q=benefits+of+high+gop+settings+in+videocameras%5C#hl=nl&rlz=1C1CHMR_nlNL339NL343&sa=X&ei=WBZLTqidBNCh-QbDpvD2CA&ved=0CBcQBSgA&q=benefits+of+high+gop+settings+in+videocamera's%5C&spell=1&fp=1&biw=1414&bih=802&bav=on.2,or.r_gc.r_pw.&cad=b

the first pdf is interesting

bannedindv

Any hints on stable, attractive gop1 settings? Sorry I'm at work so I can't test yet :(

stoney

As Vitaliy suggested, let's double GOP size. I'm a fan of GOP3. So I'm moving on to GOP6.

danyyyel

Since the release of ptool 3.62 this thread has gone very quiet and I have seen a lot of talk towards moving from 3 to 6 gop. Is it not defeating the idea of the low gop look and does 3.62 work well with 3 gop and lower. No news from Kae and Butt about some high and stable settings.

ivan858

@danyyyel all the action seem to be in the stable settings thread. 60mbs is standard issue at this moment.

stoney

3.61d GOP3 produced very small B frames.

3.62d GOP3 is producing very big B frames. It seems logical to stretch GOP longer. Added benefit would be better blending between 24p GOP6 and 60p GOP6.

cbrandin

Are the B frames bigger with GOP 6 too? Big B frames seems like a good thing to me - almost like AVC intra. Isn't that the idea behind GOP 3?

Chris

stoney

In low lighting, GOP3 produced two B-frames that were slightly bigger than one I-frame where each I-frame was about 5Mb.

As GOP size increases, it increased I-frame size where B-frame size remained about same with spike in P frame size. So that increased I:B ratio. But I think short GOP people prefer lower I:B ratio. If we find a way to increase B-frame size, that would demand high overall bitrate which would increase the chance of failing. Since GOP3 gives smaller I-frame, it may actually stabilize the system. In that case, AQ3 might be too high. It failed my highly detailed scene test. I will give one more try on 88Mbps GOP3 AQ1 24H.

cbrandin

That makes sense. I think the codec sets up a budget for I frames per second. A higher proportion of I frames would naturally result in smaller individual I frames. The B frames are simply allowed to get big enough to use up the additional bandwidth.

Chris

stoney

+1.

Higher I-frame size means more detail, but that implies B-frame has harder time to catch up with change between frames.

Taming I-frame size gives more allocation on B-frame. Lower I-frame size gives more room for shorter GOP. But high AQ value might trigger frame size going wild causing camera failure. But lower I-frame size might give lower low lighting performance.

That's my guess. I can't test it now...

cbrandin

The problem with not setting a high AQ value is that the additional bandwidth does not contribute to individual frame quality. I'm not sure adding a lot of bitrate without also setting AQ to a high value results in improvement that is very visible. High AQ values result in image improvements that are clearly visible. I suspect you would be better off setting AQ to three and then finding the highest bitrate it can support, rather than finding the highest bitrate and then the highest AQ value that still works.

Of course, all tests are useful, so keep going!

Chris

stoney

I wanna keep going... but I have like only 30 mins each day during daytime. 15 mins in the morning. 15 mins in the evening. I'd be busy pushing and pulling my kids bikes. I got time at night but can't test this at night. That's why I didn't volunteer for AVCHD ST team.

It will take me weeks. Hopefully some people with more time can pick up the slack.

Vitaliy_Kiselev

@stonebat

We'll look into GOP related things.
It just requires time.

Butt

PTool 3.62d: who has a stable setting for GOP1?

cbrandin

@Butt
nobody... We have to wait for a fix from Vitaliy.

Chris

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