MXF Avid Atom to OP1a 16:9 error

  • Agustin Trapero

    Agustin Trapero - 2014-05-04

    Hi, I use bmxtranswrap to convert Avid MXF Atom files in Op1a files. The MXF seen to be good, but the aspect ratio is incorrect.

    The proyect is SD Pal 16:9. I use the video and audio from the folder Avid mediafiles\MXF and rewrap:

    bmxtranswrap -t -p op1a --ps-avcihead -a 16:9 --group "Avid Mediafiles\MXF\op1a-TEST_v.mxf" "Avid Mediafiles\MXF\op1a-TEST_a1.mxf" "Avid Mediafiles\MXF\op1a-TEST_a2.mxf"

    Open the file in VLC show 4:3 and after 10 second the window change and show video in 16:9. And randonly change again to 4:3.

    I use de -a 16:9 setting but no luck.

    Any ideas?

  • Philip de Nier

    Philip de Nier - 2014-05-05

    Aspect ratio information can be present in the MXF wrapper and also in the essence bitstream. Decoders/players will often use the information in the essence bitstream and ignore what is set in the wrapper; this seems appropriate given that normally a wrapper would duplicate metadata that is in the bitstream. I guess that is what VLC is doing.

    The '-a' option sets the aspect ratio in the MXF wrapper only. The --bsar will set the same aspect ratio in the D-10 essence bitstream as well. I haven't yet implemented it for DV, but that should be fairly straightforward.

    Is your essence D-10 or DV? If it is D-10 then try the --bsar option.


  • Agustin Trapero

    Agustin Trapero - 2014-05-05

    Hi Philip, the essence is DV50.
    I will be happy to try it when you implement option aspect ratio in DV essence
    Meanwhile what I can do?
    Extract the essence of Atom MXF, 16:9 reformat and re-wrapp with rawtobmx?

  • Philip de Nier

    Philip de Nier - 2014-05-06

    It'll be a shame if you had to reencode it, but that approach would work.

    If you are able to you could try modifying the bitstream (in or outside the MXF wrapping) using some script rather than reencoding it. See bmx/src/essence_parser/DVEssenceParser.cpp for information about where the aspect ratio sits in the bitstream. It looks like (I haven't checked) it is the 3 lsb of the byte 455 from the start of each frame.


  • Agustin Trapero

    Agustin Trapero - 2014-05-08

    Hi, thanks again for the reply, but I have no idea how to make that script. I'm not a programmer. I've looked the DVEssenceParser.cpp archive but I don´t understand. Could you tell me what are the steps?

  • Philip de Nier

    Philip de Nier - 2014-05-08

    Sorry, I don't have a explanation of how to fix it if you're not a programmer.



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