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Official Low GOP topic
  • 1003 Replies sorted by
  • Vitaliy_KiselevVitaliy_Kiselev
    @stonebat

    I think you don't understand that I mean.
    This is 117Mbps ProRes 422 and 10bits
    http://en.wikipedia.org/wiki/Chroma_subsampling

    1920x1080 422 raw frame 8Bit=2073600+2*1036800=4147200 bytes
    1920x1080 422 raw frame 10Bit=4147200*(10/8)= 5184000 bytes

    117Mbps/24fps=4,875Mbps/frame = about 610Kb/frame

    As you can see, it is 1:8.5 :-)


  • stoneystoney
    So you saying, if 1:8.5 is good enough, why not 1:11.6?

    Then what's the point of having B and P frames if 2Mb I-frame is good enough for 4:2:0 8bit?
  • Vitaliy_KiselevVitaliy_Kiselev
    @stonebat

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

    AVC-Intra 100:
    - nominally 100 Mbit/s, size of each frame is fixed
    - CAVLC entropy coding only.
    - All formats are High 4:2:2 Intra Profile, Level 4.1
    - 4:2:2 chrominance sampling
    - 10Bit

    Let's recalculate to our case (4:2:0, same CAVLC, 8Bit) keeping compression ratio :
    100Mbps*(3110400/4147200)*(8/10)=100Mbps*0,75*0,8=60Mbps

    How about that?
  • stoneystoney
    So u saying 60Mbs should be good enough for AVC-Intra 4:2:0 8Bit?

    Then how to explain better low light performance at 88Mbps?
  • stoneystoney
    ProRes 117Mbps… 117/24 = 4.9Mb per I-frame. 33Mb per raw frame from 4:2:2 8bit output. Then HDMI recorder records it at 1:7 compressions.

    4:2:2 8bit output + GOP1 + HDMI ProRes 117Mbps recorder... Happy marriage? Holygrail? Kumbaya moment?
  • stoneystoney
    But wait... wouldn't AQ4 might require higher Mb size for I-frame on highly detailed scene?
  • driftwooddriftwood
    Don't forget, the Sony pmw F3 (£11 grand) only records at 35mbps in 8 bit 4:2:0 to sxs cards. Its only the SDI which outputs at 10 bit. The GH2 with Vitaliy's hack is providing amazing results.
    @bwhitz yes. 3.62d
  • MihuelMihuel
    My greed was punished;.) Loaded the settings @ driftwood, but changed the bitrate to 66Mbits and AQ to 3 for 24. Unfortunately, Windows Media Player, Home Cinema, playback is very stuttery.
    66Mbits 1GOP.JPG
    1288 x 667 - 154K
  • stoneystoney
    Bits making heartbeats ;)
  • Vitaliy_KiselevVitaliy_Kiselev
    @Mihuel

    Find 1080p24 T4 table in testers section and set it to 1080p24 T1.
    Must help with cadence.
  • driftwooddriftwood
    @Mihuel I already tried 66mbps and AQ3/AQ4 to no avail ;-)
    @Stonebat Yep, no probs editing the 1 GOP
  • MihuelMihuel
    @driftwood
    can my card is too slow?
    @Vitaliy
    I changed the table in 1080p24 T4 testers section and changed it to 1080p24 T1. Here is what I received. I still have a problem with WMP home cinema, which can easily play with the GOP 12 88 Mbits.
    66Mbits 1GOP.JPG
    1288 x 671 - 156K
  • Vitaliy_KiselevVitaliy_Kiselev
    >I still have a problem with WMP home cinema, which can easily play with the GOP 12 88 Mbits.

    Most probably it uses hardware accelaration and this thing just can't work properly with high bitrate Intra coder.
    You can try decoder CoreAVC 9set to CPU only) with other players.
  • driftwooddriftwood
    100mbps GOP 1 Successful. Need to do a Pappa's deathh chart now ;-)
    100mbps GOP1.png
    1327 x 698 - 78K
  • MihuelMihuel
    @Vitaliy
    Thanks.
    I changed GOP to 3 because I've got a problem with playing clips in camera. After changing GOP to 3 , there is no problem with playing in camera and PC player :).
    I still do not understand why the GOP = 12 for the same bitrate, I frame is much larger than the GOP = 1 or 3.
  • Vitaliy_KiselevVitaliy_Kiselev
    >I've got a problem with playing clips in camera

    Try to cut few first seconds using some MTS cutting tool and put it back.
    Check how it'll behave.
  • MihuelMihuel
    @driftwood
    Just pee on the moon like a puppy:). Today I have to finish, but tomorrow I masturbated with your settings ;).
  • driftwooddriftwood
    Pappas Death Chart at 100mbps, GOP1 = SUCCESS!
    100mbps GOP1 pappas death test chart.png
    1393 x 775 - 331K
    Driftwood GOP1 100mbps - setd.zip
    397B
  • MihuelMihuel
    @Vitaly
    Interesting idea, I will try it tomorrow because my pregnant girlfriend tells me to go to bed. She is always the most important;-) (better to let her think so - a woman ...)
  • cbrandincbrandin
    1:11 corresponds to a QP of 27 - that's less than half the detail of the factory 24H settings, which use a QP of 20. That corresponds to a 5:1 compression ratio on I frames best case for factory 24H. The P and B frames compress a lot more, but hopefully retain detail from the I frame.

    These I frames are around 300KB - that's pretty low. Don't bother setting AQ to anything above 0 - at these I frame sizes it won't make any difference and setting it to a higher value will probably cause problems. If anything, try setting the QP setting in the tester section higher than 20 - like maybe 26.

    Chris
  • cbrandincbrandin
    @ driftwood

    Now, that's a nice result. The I frames are 600KB, close to factory 24H I frames, so a QP setting of 20-21 (or, AQ=0) is perfect.

    Good work!

    Chris
  • driftwooddriftwood
    @cbrandin Ill give it a try on the QP settings. First just finishing off a 100mbps 3 GOP test ;-)
  • Vitaliy_KiselevVitaliy_Kiselev
    >These I frames are around 300KB - that's pretty low.

    See my calculations above.
    My understanding is that if you use intra coding more highly compressed I frames are much less visible as you do not have compression artefacts propagation on decoder stage.

    So, without going to extreme numbers we need to make completely stable and workable intra mode (up to about 100Mbps).
    Plus GOP 3, I think.
  • cbrandincbrandin
    I worked out the theoretical numbers. It looks like @driftwood has just about reached the theoretical limit for GOP1 at 100Mb. The detail quality should be equivalent to factory 24H - assuming detail doesn't degrade with P @ B frames - which it shouldn't with static shots (motion is something else altogether). This is very impressive.

    Going through the math for GOP 3, I calculate that using a AQ of 1-2 should just about hit the sweet spot, yielding I frames of up to 8-10 Mb at 100Mb bitrate. If that works out it would be spectacular. Now, unless you set FBx and frame limit to 1.5x the original values, you won't get I frames above 8Mb. If that works out - these will become the settings I use personally!

    Chris
  • driftwooddriftwood
    gop 3 100MBPS - Pappas Death Chart = Success! Same settings as my previous GOP1 test - just change to GOP3. Now going to do some of Chris's QP tests on both.
    100mbps GOP3 pappas death test chart.png
    1393 x 746 - 288K
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