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Official Low GOP topic, series 2
  • 1022 Replies sorted by
  • @Kae -- hope you get better man! Your 3gop setting was superb on my last shoot.

    You beat me to it by a few minutes but can also confirm no problem with spanning, Avid import or playback on mac (with MXplayer).

    @Driftwood, have you played around at all with the 720p 60p settings? I have to use that a fair bit and was curious if you had any starting points for experimentation there.
  • @Kae - you are one of the really great voices here, Kae. Please know that we here send our best thoughts and wishes to you and yours. Godspeed, quick recovery, and thank you for being a part of the community.
  • what are record time looking like... IDK the conversion say an 8gb card
  • @cosimo_bullo

    Thanks so much for the kind words. Actually I beat the big C 100% but it was a bitch and I'm recovering, but not as big of a bitch as finding stable 1 GOP :-) !
  • Hi @kae, at the moment the bitrate you'll notice is being held back on a limiter... I wanted to 'get there' somehow, this is now achieved, but now its down to fine tuning and it'd be great if everyone could get involved more and help make this work - you know - really push the gh2 to its limits and get quality. If we can't, then its back to good old GOP3, which, because of this test will only improve too. Even great 6 GOP hasnt been truly established yet.

    Whether we get it to span like this latest setting is another matter, because with these encoder settings we can now (hopefully) rid ourselves of the dreaded 2nd frame 'P' from GOP 1.

    We have to seriously look at what the encoder settings are doing and some of the other ones that Vitaliy has provided. Its taken me a day and half of tests just to get this stable. Ive made some crazy errors - I actually thought I'd found 25p at one point in 1080i50.

    Ive got 50i, 72050p stable and 1080i60 (all at GOP1) but indeed, poorer quality than GOP3 upwards. By achieving this, the hardest setting first should in theory help us go beyond and and improve the quality. And no doubt I believe the GH2 has got more in the kitty to offer. Who knows what the next ptools could offer? I know people hate the high bitrates, but GOP3 hi quality and certainly GOP1 needs the bitrate - theyre hungry beasts!

    The GOP1 24p is the best of the bunch Ive tested and Ive filmed with it daytime today and it looks very good in daylight. However, I would say in darker settings this will not perform anywhere near as good as 132M GOP3, but if we can get it close - all the better.
    In a few weeks we will be beyond this stage, I sincerely believe that (perhaps a few days ;-) who knows?)
    It's been fun getting there and you @kae have encouraged me with your original GOP3 to go beyond - sometimes the simple answers are there before you - this is why I suggest to all testers to try everything, don't give up, dont rush and be methodical - and write it down/spreadsheet it. It saves acres of time and you have something to refer to later.
    Anyways, Im too tired to finish GOP1 720p60 (it probably wont be worth it - but who knows?!)

    What we need to do is establish the limits and then work backwards.

    This, I believe, is a great start. PS Yeah congrats on taking on the bigger mission - life!
  • At this stage Ive found (like @kae) the 3000000 vid buffer is pretty handy at 720p to give you a start ;-). I'll be uploading a GOP1 starter base patch tomoz covering all of them at GOP1 (and working!) bar the 720p60 which will probably left at GOP3. I'm off to kip fellas, night!
  • Thanks driftwood! Give us our marching orders for perfecting this tomorrow. Can't wait!!!
  • driftwood,
    First of all, you are right, your 244M looks good and passes all of my extreme tests.

    As you mentioned in your last message, hopefully we can find a way of bringing up the bitrate.
    The real question is which is better:
    i-frames at 12GOP ~ 1.1M or i-frames at 1GOP ~ 640K?
    I believe for image quality the answer is the larger i-frame at 12GOP, but i'm not 100% sure? Anyone?
    But, for motion is another story.

    Also, i'm hoping we find a way to bring up the bitrate, since your 1 GOP looks smooth for cadence.
    Here's a quick comparison:

    244M 1GOP
    88M AQ2 MAX VARIATION
    TEST:

    Target: Strays new Extreme Denser chart
    Light: No Ambient. TWO 250W 5K Daylight lamps
    f5.8
    1/1600
    ISO3200
    STATIC TEST (1 minute); PAN (FIXED SPEED MOTORIZED) ~20 Seconds

    Streamparser images:
    DRIFTWOOD 244M 1GOP 110925 STRAY EXTREME DENSE.png
    STRAY 88M AQ2 MAX VAR.png
    DRIFTWOOD 244M 1GOP 110925 STRAY EXTREME DENSE.png
    1920 x 1080 - 534K
    STRAY 88M AQ2 MAX VAR.png
    1920 x 1080 - 150K
  • @driftwood
    Dude, I go away for a week and you completely rock it! Amazing work! GOP1 like butter... and in every tool, no less. Just bloody fantastic.

    Now, how can we get the bit-rate up? :D

    I'm excited
  • @proaudio4 "I believe for image quality the answer is the larger i-frame at 12GOP, but i'm not 100% sure? Anyone?
    But, for motion is another story."

    That is my understanding too, but it's not another story for motion, there are too many vagaries with the codec (and a shot). Large I-Frames do not necessarily mean bad motion rendering. Also, the GOP1 is using only half of the bitrate (looking at the averages) that its been set to as well, which on a deathchart is very weird. Soo... it needs the bitrate for stability but will never, ever, reach it ?

    @driftwood or anyone. Can you explain how elecard can show how the buffers were functioning during recording from analysing the stream afterwards ?
  • Just as an experiment I set my 88M max variation to GOP1 to try and confirm some things, I changed nothing else except the GOP size. It isn't stable on deathcharts unsurprisingly and does have the rogue P-Frame. However, it has confirmed something to me about bitrate usage at GOP1, which is it stays high even on AQ2 in lowlight. On the shots I took it was always running at an average very close to the maximum, so if you are running at GOP1 don't worry too much about pushing AQ. I expected this to be the case, but hadn't got around to seeing if it was true.

    On all shots the I-Frames collapse in size at around frame 16 to 20 consistently. so thats the point where it runs out of bitrate and adjusts I-Frame size downwards. this could also be due to it being a max variation patch it allows the codec more possible QP settings. From that point it does remain consistent for the rest of the shot (it being static). Notice in the lowlight graph that if it starts at a lower size it remains consistent. This fits with Driftwoods clamping of the I-Frame size solving the problem. What I feel is that a GOP1 with I-Frame sizes comparable to the 244M is therefore possible at a much lower bitrate than the 240M (as its pretty close to the 244M results in the lowlight shot to the 244M deathchart test). But yeah, the relationship between I-Frame size and bitrate is going to be exponential in some way I guess at GOP 1. Now, I'm saying this without trying to cure the rogue P-Frame issue, which again could also lower the I-Frame size more, but I don't know if thats true yet.

    edit : Oh yeah, I didn't move the camera about, that definitely needs doing. Will upload findings in a few. Answer : It gets a bit messy, exhibits cadence problems, however the positive from it is that it is capable of spikes in I-frame size back up to large I-Frames when required (but can't hold them obviously, hence the cadence).
    lowlight ISO320 softlens 50ss.png
    1297 x 683 - 410K
    Deathchart ss400 ISO1600 88M AQ2.png
    1297 x 683 - 484K
    Motion and Detail 88M AQ2.png
    1294 x 682 - 438K
  • So, at 244M aren't we moving toward Arri Alexa bandwidth? ProRes 4444 has a bitrate of 330Mb/s (remember HDCAM SR is only 440Mb...) It also has 12 bit colour depth. So, how is AVCHD's compression method compare to the much older ProRes? AVCHD 244Mbs<ProRes 330Mb/s. And we are 8 bit and they are 12bit. So bit for bit we may be on par?
  • @disneytoy -- oh were it so. Remember a few things: first, bit rate is far from everything -- the alex is an $80,000 german engineered small supercomputer, combined with a far more advanced cmos sensor that is able to extract an incredible 14 stops of latitude. From my testing, the best hacks may have been able to squeeze out another stop of latitude, but that's it. Even at pro res 422 HQ you're getting 10 bit colour, which means millions of colours instead of 256. It's a big difference. And finally, we're stuck at 420 colour.

    The work of driftwood and others is amazing but we should be careful about going to far with comparisons. From my experience the gh2 is still struggling for acceptance in the professional market and overstating our case will not help it knock off the 5D :-)

    PS: We're also getting off topic. This should only be for testing and posting low GOP hacks, not comparisons to other cameras. If you like, please post something on my thread comparing the gh2 to arri to f3 and I'd be happy to discuss more.
  • At present with the latest GOP1 244 we are using 2 thirds of the maximum i frame capability to remain stable. For anyone testing: lift the 24 frame limit up in very small increments (say 100000 at a time) and adjust other areas now to try and get the frames up.
    This would entail looking at cbrandin's theory of maximising the iframe quality or other settings not yet understood by the testers.

    42M/60M Video buffers: Anyone got them working in any mode? I believe we would need more bitrate beyond 244 (265M is currrently tops) to experiment with say the 42M/60M video buffer and I'm not sure if that would be possible/available in the GH2. Only Vitaliy would know.
  • Im interested in seeing this new GOP1 244m footage converted to cineform raw 4:2:2 10 bit...
  • @driftwood
    If I understand correctly: now 1080p24 frame limit = 5111808 do you propose to increase the contribution amount, eg by 100000, the result will be 5211808 ? What do you mean by "and adjust other areas"?
    Is there a possibility of limiting the lowest value of the size of frame?
  • @Mihuel that should be something AQ does, or setting the QP manually. However at GOP1, from what I can surmise limiting the lowest value shouldn't be necessary (it seems to try the max QP setting for I-Frames as it is, within the range it has been given). Plus if you could it would just increase the chances of instability, and increase them considerably too. You've got to give the codec enough of a range to adapt within after all.
  • @Stray
    Thanks, I understood. My misunderstanding stems from the fact that in the current settings @ Driftwood has not selected the AQ or QP. It is also about to pull out too many details of how the dark parts of an image.
  • @driftwood Yep its a good strategy of driftwoods, basically go for stability at GOP 1 first (and kill that P-Frame) then tweak it afterwards to get decent image quality and bitrate usage. My own instinct is AQ and QP are not that important when running at GOP1. I also reckon we'll end up with a bloody good GOP 1 at a lower bitrate.
  • The current Driftwood settings are working fine for me with a Sandisk Extreme (30 MB/s), but no spanning here (as reported by Daimon). A Transcend class 10 quits after a few seconds.
    PPro Cs 5.5.1 is playing the footage without a hiccup on last years MacBook Pro.
  • GOP1 footage, dont know who from...
  • Did another test, this time not moving trees with heat shimmer at 640 ISO, but a street with some cars and bicycles passing @ 160 ISO. Spanning fine for 30 minutes in 5 chunks, delivering an average of 90 mbps.

    Doesn't play in camera, but in PPro (with minor screen redraw problems if I try to check stills). Once I force a redraw, I can step though motion in all it's intra glory. OMG, this is great! A new camera.
  • I agree, the 1 GOP looks great. I hope we can find a way to bring up the i-frame size and maintain stability.
  • @nomad
    Are you tested the last settings Sir Driftwood GOP 1? I have no problem with the playback in the camera.
  • ITs there any chance of making GOP patches for GH13 ?
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