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Bitrate on P3A

Discussion in 'Pro/Adv Discussion' started by lenmcgilvary, Dec 31, 2015.

  1. lenmcgilvary

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    I just recorded a short video on my P3A 2.7K in both MP4 and MOV and get a bitrate no more than 20Mbps. Here is the info from the .mov file.Does DJI not say its 40Mbps. Recorded on cam, not lightbridge card.
    Screen Shot 2015-12-31 at 12.18.59 PM.png
     
  2. alokbhargava

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    Your file is JPEG 2000 compressed. Check raw file for the exact values.
     
    #2 alokbhargava, Dec 31, 2015
    Last edited: Dec 31, 2015
  3. lenmcgilvary

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    my thinking too, is there a setting im missing
     
  4. alokbhargava

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    Analyze raw file.
     
  5. John Locke

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    20Mb/sec X 14 sec /8 = 35MB (close to 33.6MB). So it appears the calculation is right, it's just a low bitrate, which the Advanced has been known to have, versus the Pro. It appears the MP4 compression at the camera is the issue. I always thought that H.264 compression has to be done in hardware at the camera to conserve power and weight, however someone here said the Advanced model had a firmware update to increase the bitrate to be on par with the Pro. I'm in disbelief, but anything is possible I guess. I read that the Pro has a TI DSP in the camera that the Advanced did not, implying some advantages in speed.
     
    #5 John Locke, Dec 31, 2015
    Last edited: Dec 31, 2015
  6. alokbhargava

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    You should also divide by 1.024 and 14 sec is an rounded value not exact. Numbers are very close. Bit rate is thus correct, rate depends on the data to be transmitted and in this case all data could be transmitted at this bit rate. Change the fps, bit rate will change and it will be limited to the max specified value.

    Bit rate is image bits x fps

    Image bits vary from image to image in each frame in compressed images but are same in raw image.
     
    #6 alokbhargava, Dec 31, 2015
    Last edited: Dec 31, 2015
  7. John Locke

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    Just to confirm, you pulled this 14sec video right off the SD card, right?
     
  8. lenmcgilvary

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    thats correrct, from the sd card
     
  9. lenmcgilvary

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    Perhaps i should mention the card is 64GB UH3
     
  10. Mad_angler1

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    The Pro has the Ti DSP that handles the LB feed at 720p , the Advance does not have this so the A9 has to encode both streams onboard using its internal DSP for both. This means resources are stretched across the 2 feeds compared to the Pro that has the A9 dedicated to camera to card.


    Sent from my iPhone using Tapatalk
     
  11. alokbhargava

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    OP is not discussing transmission over air. He is talking about recording on SD card.
     
  12. SPPhoto

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    P3A - bitrate test

    Hi All - Just updated to the latest firmware and did some testing to see if there was a substantial difference between the 25fps and 50fps bitrate. I was thinking that if the 25fps used the same bitrate as 50fps which had to spread the bits over twice as many frames the 25fps results would be that much crisper.

    1080 - 25fps = 25mbps
    1080 - 50fps = 40mbps

    (Haven't looked into 2.7k yet)

    I was very interested in the bitrate after editing some footage from the local coast line and noticed some blocking artefacts in the water with subtle colour gradients, after post processing and export I might add. SOOC the footage has few noticeable artefacts both at 25fps & 50fps and both respond well to processing in AE but do much better from adding in a few extra mbps to compensate for the additional compression. 25fps 25mbps upped to 40Mbps on output and 50fps 40mbps upped to 60mbps both look very good.

    2.7K is next but if its only 40mbps why bother?

    S
     
  13. SPPhoto

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    just did a quick flight and...

    2.7k 25fps = 45mbps from camera - (I wish I could get 1080 25fps @ 45mbps!)

    Exported the footage - 1080 @ 25 - 1080 @ 50 - 2.7 @ 25 of a forest with plenty of wind blowing the leaves @ CBR 80mbps and they all look good. But by far the 1080 renders look better with the 1080 25fps looking slightly better.

    so

    2.7k 25fps 45mbps = 1.8mb per frame
    1080 50fps 40mbps = 0.8mb per frame
    1080 25fps 25mbps = 1mb per frame

    So considering 2.7k @ 25fps is 2.5 x bigger in pixel amount than 1080 but the bitrate is only 1.8 x bigger then 1080 @ 25fps (45mbps Vs 25mbps) there is a pretty big short fall. There is only a 20% loss in per frame data between 1080 50fps & 1080 25fps.

    I'm going to stick to 1080 and depending on subject and/or final output switch between 25/50fps.
     
  14. atverycore

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    I'm getting 60mbps at 1080p 60fps (NTSC) and 45mbps at 2k 25fps.
    Didn't noticed much difference so I prefer to shoot 2k and downscale it to 1080p.
    The Pro does 4k at 60mbps so I guess it is possible to get 60mpbs at 2k or 1080p 25fps on the Advanced but for some reason DJI limited almost everything to 40mbps.
     
  15. SPPhoto

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    60bmps! - geez if DJI gave the 1080 that pipeline it would be such amazing footage - I'm working on a project where we have 2 x 5D mk3's for filming and I just want to get the Phantom as high as possible.