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Official Low GOP topic
  • 1003 Replies sorted by
  • 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 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

    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 :-)


  • No_SuRReNDeRNo_SuRReNDeR
    I cant wait to see some awesome GOP1 footage-



    Star Trek_ Simon Pegg as Scotty (rus subtitles).flv_000089000.jpg
    549 x 312 - 49K
  • stoneystoney
    100Mbps read throughput is non-issue for 7200 rpm hdd. 1:1 compression might run into disk read speed bottleneck.

    If HDMI recorder can record reliably at 117Mbps, 117/24 = 4.875Mb per I-frame at GOP1. But average write speed of 7200 rpm hdd is around 12MB/s or 96Mbps. Hmmm... the speed might go lower.

    If stable write at 117Mbps, 1:6 compression. Not bad. Actually that sounds pretty good if I-frame compression is better than JPEG's.
  • Vitaliy_KiselevVitaliy_Kiselev
    ProRes422 1080p24 bitrate for 10bit 422 (not HQ) - 117Mbps
    http://www.appleinsider.com/articles/07/04/18/a_closer_look_at_apples_new_prores_422_video_format.html

    @stonebat
    Normally the lower the GOP - the faster is NLE :-)
    Compression do not matter much unless your disk or cpu are extra slow (in this case lower compression will be slower).
  • stoneystoney
    I tried GOP12. I-frame averaging 8Mb. 1:3 compression. NLE was much easier than clips from unhacked body.

    I guess... 1:11 compression would need transcoding? @driftwood can you edit the clips easily without transcoding?
  • No_SuRReNDeRNo_SuRReNDeR
    :)- Its hard to see cause its white like b-ground even I didn't see it at first.
  • bannedindvbannedindv
    oh duh - I had to log in to see that. Thanks.
  • No_SuRReNDeRNo_SuRReNDeR
    @driftwood Can you upload the clip(s) to Vimeo or something?
  • No_SuRReNDeRNo_SuRReNDeR
    @bannedindv He did, look to the far right of the two images - download the zip file...
  • bannedindvbannedindv
    @driftwood - could you please post your GOP1 settings as an .ini?

    I'd love to test this.
  • stoneystoney
    Oh I meant 2Mb I-frame size.

    1:11.6 compression...
  • Vitaliy_KiselevVitaliy_Kiselev
    @stonebat

    1920x1080 420 raw frame=2073600+2*518400=3110400 bytes
    I Frame size here = about 268000 bytes.
    Only 1:11 compression (and I frame compression in H264 is more effective than JPEG).
  • stoneystoney
    Average I-frame size little over 2MB. Are you sure it's big enough to capture highly detailed scene?
  • bwhitzbwhitz
    @driftwood

    Great stuff! I hope to try these out tonight! I'll let you know what I find...

    You're using these setting with Ptools 3.62 right?
  • driftwooddriftwood
    Hang on, Just tried my 36 GOP settings switching down to GOP 1 and got these amazing results.All intra frames, passed the Pappas chart of Death (still going after 2 minutes). Just what is wrong with the 3.62 GOP settings Chris/Vitaliy? Kae/Anyone try my settings out for me to confirm. Is 50mbps the sweet spot?
    Chart below were taken on pappas death chart btw.
    Also shot 5 minutes of footage and got nice looking images. Nice staccato!
    Short GOP 1 - 50bitrate test using ptools 3.62 .png
    1312 x 704 - 88K
    Short GOP 1 - streamparser time mode - 50bitrate test using ptools 3.62 .png
    1306 x 695 - 80K
    Driftwood GOP1 50mbps - setb.zip
    411B
  • bwhitzbwhitz
    @driftwood "Tried the new ptools 3.62, and because of the weird short GOP problems am sticking to the old ptools Kae settings."

    +1 me too. These settings are great! The only thing that could top them would be GOP-1. The motion just looks too good to me to raise the GOP. I heard they were trying GOP-24 in another thread! What!!! Just take still pictures and animate them in after effects at that point! I don't get it! High-GOP motion looks like Flash animation.

    Also, with Kae's extreme settings sometimes I get a weird bug where the camera will tell me that it can't play back the file... but then once I record another clip, it'll play back fine... anybody else getting something like this?
  • driftwooddriftwood
    Tried the new ptools 3.62, and because of the weird short GOP problems am sticking to the old ptools Kae settings. Got some wonderful speedboat / water shots using kaes 3GOP. Any news on when the GOP fix is coming? Tried out a few 1 GOP settings and same problem Kae was getting with his latest 3GOP test - low bitrate.
  • olegkalyanolegkalyan
    tested 65 3 gop vs 44 6 gop Kae settings, drummer hands, we could see the differense in motion blur, 3Gop having more film like.
  • bluesblues
    loaded my GH1 using ptool 3.62 with transcend class 10 card and i have gop1 at FH 88000000 and 55000000 H am hitting 50mbps bitrate indoors and no problem so far, will test outdoors
  • bluesblues
    what would be a low gop settings using ptool 3.62 for gh1
  • alcomposeralcomposer
    @bwhitz
    Long GOP was invented for the same reason MPEG2- MPEG4- H246 etc was invented. (or part of really). As a way to distribute digital assets easily - at a low quality to fit on a DVD.

    They noticed that at the end of the day - most of the motion in video is still- so no need for a new frame every frame! I think that most professional mastering houses (probably not now) used to put in markers to let the encoder know when was the best time to put in more I frames as opposed to B, P frames. (car chases etc).

    And without Long-GOP even 25gig wouldn't really be enough for a Blu-ray really anyway... but that is not where the industry is at right now anyway. I believe currently the industry is still trying to work out online distro- and making money online- and what the F$*K they are going to do with 3D now that they have it...
  • bwhitzbwhitz
    @kae "And please don't answer 'set GOP to 12 or 6', I'm interested in 3. "

    haha. me too. GOP 3 or lower... ;) I'm addicted to the blinky-sticatto film motion.

    I'm wondering why long-GOP was ever implemented. What good is higher quality if the motion suffers? Did they not see that it makes everything look like 360-degree open shutter?
  • kaekae
    @cbrandin

    Thanks, Chris! I was gone for awhile so trying to catch up. I'll quit testing the 3 gop settings then until it's fixed.
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