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    Possible breakthrough on Native 24p!
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    I've been digging into the GH1 firmware code and found that overall bitrate appears to have a big effect on the maximum speed that flash memory writes can occur. I’ve always wondered why the write speed error comes up in AVCHD mode when clearly the data rates are well below what the card can handle. I think I found the answer.

    When the write speed error comes up it’s because the calculated maximum write rate has been exceeded – whether the card can handle more or not. I tried the Lpowell settings but changed two things: I doubled the overall bitrate to 86,000,000 and I checked Native 24p. Upping the overall bitrate nearly doubled the calculated flash write rate (i.e. the fastest write rate the camera attempts to write to flash). It appears to be working! I’m not getting any lockups and the clips look great. I tested this with highly detailed scenes, fast shutter speeds, everything I normally do to break the codec and it seems to be standing up.

    We probably need to do some fine tuning and more testing (hint, hint, Lpowell), but so far it’s looking pretty good. I ran my tests with a Transcend class 10 card.

    Chris
    Last edited by cbrandin; 09-12-2010 at 02:02 PM.


     

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    May be you are right here. :-)
    It can be good news, as native is much more usable :-)


     

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    #3
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    Eagerly subscribing to this thread!


     

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    #4
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    Lol. Right when I thought I had a pretty good setting , I found this thread. I'll test this out as well.
    ryankozicki.com | Panasonic GH1 |


     

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    #5
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    The theory behind this is that Native 1080 24p frames are twice as large as 720p and wrapped 1080p frames. The overall bitrate affects the instantaneous maximum write speed. With frames twice as large I surmised that the instantaneous write speed would have to be correspondingly faster. The video bitrate keeps the average bitrate over time to a manageable level.

    Lets hope this holds up.

    Chris


     

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    My latest theory was that it is not bitrate at all, but rather time related constant (being multiplier of 90000 ticks) :-)

    May be it is good to look at all 18.000.000 locations and check routines logic carefully.


     

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    #7
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    Yeah, that makes sense to me. At first I thought it was buffering too, but now I agree, it has more to do with transferr rate and write frequency. Youll notice that the pre-calculated minimum interval between writes is much smaller (the first four bytes of each 192 byte packet are the internal time stamp and the difference between them is the write interval) with the overall bitrate set high. The interval between packets is always a multiple of this pre-calculated number. Thus, the minimum interval absolutely limits the maximum frequency that packets can be written.

    Chris


     

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    There are still a few things about the Native 24p streams that are a little strange - like an extra P frame every now and then and an empty frame also. It doesn't seem to affect how the clips look, though, so I'm not sure what to make of it. Also, I've seen some of this with 720p clips. It wouldn't be visible with wrapped clips because of the pulldown, etc... We might just be seeing artifacts that always existed and aren't related to the hack.

    Chris


     

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    #9
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    It is very interesting thoughts.


     

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    Quote Originally Posted by cbrandin View Post
    There are still a few things about the Native 24p streams that are a little strange - like an extra P frame every now and then and an empty frame also. It doesn't seem to affect how the clips look, though, so I'm not sure what to make of it. Also, I've seen some of this with 720p clips. It wouldn't be visible with wrapped clips because of the pulldown, etc... We might just be seeing artifacts that always existed and aren't related to the hack.
    Chris
    Most probably this strange things happen in original code.
    First, this is due to architecture used (very hard to test).
    Second, routines have so many hardcoded things, I am amazed.


     

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