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    AVCHD encoder research
    #1
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    Reserved.


     

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    #2
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    Hi Vitaliy,
    I posted two days ago a question:

    To TEster13:

    Is it possible to have two different settings for FHD and SH?

    Because as I understand we have SH: 17Mbps, H: 13Mbps, L: 9Mbps all 720 60p

    It seems that settings for AVCHD in Ptool do not affecting H and L.

    I did quick a test with H and I got 12Mbps with hidetail scene. I used C settings...
    My Idea was that we can use C settings for FHD and SH( in low detailed scenes) and for H we could use other settings to get 30Mbps stable ( for hidetail)....
    THx


     

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    Hi, I've been testing the AVCHD setting on the GF1 and in great detail scene I can get more than 40mbit/s. that is good.
    However the compression is of the codec in detail shadows is really bad (really muddy and low bitrate). I do not now if it is happening too with the GH1 or if it is the algorithm of the GF1, would be nice to have both to compare but I don't.

    here is an example of what I am talking about: http://dl.dropbox.com/u/199525/00019.MTS
    The problem I see is that at certain point of exposure the bitrate drops massively.
    Is it possible to put a limiter so that the bitrate doesn't go under 12mbit/s or something.

    PS: I don't know if I can post here, you can move it or erase it.


     

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    #4
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    As for limiter - of course it is not possible.
    AVCHD I frame compression works like JPEG. So, it is kind of dumb. It have similar to jpeg Q tables things and they describe how DCT results will be processed.
    If you have simple or dark scene it'll result in dropped bitrate as DCT coefficients are much simpler and after same processing can be compressed much better.
    Best thing I can think of is to have something like I/P ration setting to set ration between I frame and P frame sizes in whole GOP.
    We'lls see if it is possible.


     

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    #5
    Senior Member jobless's Avatar
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    Testing 3.37d:

    It works as expected...

    Video bitrate adjustment FHD/SH 50000000
    Video bitrate adjustment H 38000000
    Video bitrate adjustment L 30000000
    Overall bitrate adjustment 52000000
    Limiting bitrate adjustment 60000000

    FHD- 37 Mbps--- No Mud, No problems with heavy pans, No problem with zooming with Kit lens, No problem on tripod

    SH-- 38 Mbps - stops recording after 10 sec on heavy pans

    H -- 32 Mbps - No MUD, No problem with pans ( 1 min 15 sec), Stops recoding after 12 sec with zooms

    L -- 28 Mbps- I can see a MUD ( but no as before) , No problems with pans and zooms

    At LOW LEVEL seme as before....

    I've tried also:

    Video bitrate adjustment L 34000000--- No MUD, No problems with pans (1min 20 sec), Stops recoding on Zooms after 20 sec


     

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    #6
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    Here is a summary of some tests I did last night with PTool 3.37d.
    Lens 7 mm, at F4.
    Shutter Speed 1/50 s
    ISO: 800
    Card: Sandisk Extreme 30MB/s

    1) Check Off:
    * Version Compare patch
    * Video Bitrate Adjustment FHD/SH Simplified -> 60000000
    * Overall Bitrate Adjustment -> 62000000
    * Limiting Bitrate Adjustment -> 70000000
    Producing nice clean footage in a wrapper. Looks good at low level too (see attachment).

    2) Add the following to 1):
    * Native 24p/25p patch
    As soon as I hit record button camera becomes unresponsive, but live view is still operating.

    3) Add the following to 1)
    1080p25 GOP Size -> 15
    Same result.

    When bitrates are lowered to P-Tool "C" settings camera records with native patch successfully.
    Attached Images Attached Images
    Last edited by svecher; 06-18-2010 at 10:32 AM. Reason: Add screenshot


     

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    #7
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    1) Check Off:
    * Version Compare patch
    * Video Bitrate Adjustment FHD/SH Simplified -> 60000000
    * Overall Bitrate Adjustment -> 62000000
    * Limiting Bitrate Adjustment -> 70000000

    Producing nice clean footage in a wrapper. Looks good at low level too (see attachment).

    2) Add the following to 1):
    * Native 24p/25p patch
    As soon as I hit record button camera becomes unresponsive, but live view is still
    operating.
    Hi there!
    Sorry if this report sould go to other thread, so if this is the case donīt doubt in delete if!

    This exact thing happened to me also (24/25p patch ticket on...), when trying to shoot in FHD mode two days ago (had to remove battery too.....), but with the same settings was able to record in SH mode without any problems...

    I was using a Sandisk Ultra 16GB Class 4 with 15MB/s of writting speed.
    Hope this helps....
    Cheers!
    Asier.


     

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    #8
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    I can get the GH1 to pulse when Native 24p is selected no matter how other patches are set - it's just a matter of shooting a sufficient mixture of detailed and flat subjects.

    Attached is what happens if the only patch selected is Native 24p and everything else is left alone (factory AVCHD/FHD settings except for Native 24p).

    I've tried A, B, C, and a plethora of other settings with GOP lengths of 8, 12, and 15. I can always get pulses.

    My conclusion is that pulsing is a product of Native 24p and that alone, although the frequency of pulses may vary.

    Chris
    Attached Images Attached Images


     

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    #9
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    Thanks.
    This seems reasonable.
    As 24p and 25p modes are completely untested by developers of actual video encoder.
    So, we see spikes in last P-frame in GOP.


     

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    #10
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    Yes, I've checked and it is always the last frame.

    chris


     

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