Thread: DNxHD 36 MXF - Large File problem

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  1. #1 DNxHD 36 MXF - Large File problem 
    Senior Member Jonathan Petts's Avatar
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    Hello All!

    I am quite new to scratch and currently in a bit of a pickle.

    I am taking over from a DIT on the third day of production and I am firing off DNxHD 36 MXF files out of Scratch.
    The problem is is that in total for a mag I am getting 7GB worth of footage - I can see that yesterday in total they were getting 220mb and sending it to the editor.

    What am I doing wrong?

    Settings -

    1080p / 24 DNxHD 36 - Range Video
    Forma : 1080 - 24
    Filter Linear
    8Bit
    RGBA
    Lin/SRGB
    Progressive
    Aspect Square 1:1
    Frame Rate - 24
    Scale 1.000
    Output - MXF AMT Export


    Any help would be amazing - I am stumped as to why the files are so large.


    Jonny
    - DIT / Lab Operator -

    http://www.imdb.com/name/nm5401988/

    Ex- RED Dragon / Epic Owner
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  2. #2  
    Senior Member MichaelP's Avatar
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    DNxHD 36 is roughly 270MB/minute (1GB = 3.79 mins). How many minutes/hours of dailies are you processing? In your case, 7GB would be about 27 minutes. Does that sound right?
    ‎"There are a thousand ways to point a camera, but really only one."
    Ernst Lubitsch
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  3. #3  
    Senior Member Jonathan Petts's Avatar
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    Thats what I worked out in DataCalc - the previous days DIT seemed to get 10mb - 100mb files and their durations around in the 1-2 min range which is close to what we are doing today (a few 7 min takes(. Where as I seem to be getting 500mb.

    I compared a 2 min take and it was 440mb - compared to 100 from the previous day.

    Is there a quality option I should be looking for ? or some other way to reduce quality?

    Much appreciate all the help!

    Jonny
    - DIT / Lab Operator -

    http://www.imdb.com/name/nm5401988/

    Ex- RED Dragon / Epic Owner
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  4. #4  
    Senior Member MichaelP's Avatar
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    DNxHD 36 is pretty much a fixed data rate and I am confused as you are as to why a similar file would be 1/4th the size unless there was a lot of audio tracks being synced and appended to the files. There is no way to reduce quality - it does not matter whether you start with an SD file or 6K file with 1/4 debayer or full, the resulting DNxHD 36 file will be the same size. If I create a 1 minute file in Media Composer directly via a transcode of picture only it is 265MB.
    ‎"There are a thousand ways to point a camera, but really only one."
    Ernst Lubitsch
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  5. #5  
    Senior Member MichaelP's Avatar
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    If the DIT was creating 14:1 standard definition media, it is roughly 1/4th the size of DNxHD 36. For the same 1 minute file it ended up being 74MB.
    ‎"There are a thousand ways to point a camera, but really only one."
    Ernst Lubitsch
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  6. #6  
    Senior Member Christoffer Glans's Avatar
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    Sounds like he did it wrong, is this the reason you took over?
    "Using any digital cinema camera today is like sending your 35mm rolls to a standard lab. -Using a Red is like owning a dark room."
    Red Weapon 6K #00600
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  7. #7  
    Member Daniel Esperanssa's Avatar
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    Hi Jonny,
    Just to be sure, let's take the "regular" steps:

    - Have your construct in 1080 (deliverables resolution)
    - Ensure all shots (assuming RED Dragon) have RED Resolution set to "Project" (You can do a Ctrl+A to select all shots and go to Media Browser/Shot Config tab to batch set resolution as well as Process quality)
    - Navigate to Output menu and add the MXF AMT export from the "Manage Outputs" dropdown
    - Use #sname token as file naming scheme.

    There's no specific quality setting for MXF AMT (it uses the Avid Media Toolkit) other than the DNxHD flavor.
    Let us know how it goes and also the Scratch build you're using.

    Good luck,
    D.
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  8. #8  
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    I see about 16.46GB for 1 hour of DNxHD36 in 1080 23.98 with 2 x 16-bit audio channels (according to the Video Space app). 7GB would be about half an hour, give or take.
    marc wielage, csi colorist/post consultant daVinci Resolve Certified Trainer
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  9. #9  
    Senior Member MichaelP's Avatar
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    Marc's numbers are in line with what to be expected and the numbers I got from actual transcodes.
    ‎"There are a thousand ways to point a camera, but really only one."
    Ernst Lubitsch
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