[FFmpeg-trac] #9271(avdevice:open): Get color information from source device

[FFmpeg]

#9271: Get color information from source device
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             Reporter:  Diederick    |                    Owner:  (none)
  Niehorster                         |
                 Type:  enhancement  |                   Status:  open
             Priority:  normal       |                Component:  avdevice
              Version:  git-master   |               Resolution:
             Keywords:  dshow        |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by Diederick Niehorster):

 Seems i failed to attach the updated patch, sorry. I have attached a new
 one where I also convert chroma location (one unknown to me there, DV PAL,
 which is horizontally and vertically cosited: http://www.adamwilt.com/pix-
 sampling.html, https://docs.microsoft.com/en-us/windows/win32/api/dxva2api
 /ne-dxva2api-dxva2_videochromasubsampling).

 I also added the "newer" color spaces/trcs. They are not in DirectShow,
 one needs to use mediafoundation for those. Stupid since DirectShow isn't
 going anywhere... I did note that the enum values provided by both
 DXVA_VideoTransferFunction and MFVideoTransferFunction (and also
 DXVA_VideoPrimaries and MFVideoPrimaries) match and that the bitfields in
 DXVA_ExtendedFormat are sufficiently large to contain the additional
 values in the MFVideoxxx enums. Interestingly, MS even presents example
 code that wholesale plops the MFVideo values into a DXVA struct:
 https://docs.microsoft.com/en-us/windows/win32/api/dxva2api/ns-dxva2api-
 dxva2_videodesc. So perhaps thats unofficially supported, and maybe some
 devices use it. I see it used in the wild in software at least:
 https://github.com/Nevcairiel/LAVFilters/blob/ddef56ae155d436f4301346408f4fdba755197d6/decoder/LAVVideo/Media.cpp#L752.
 So i have just included those values too, in the worst case they do
 nothing. Can you check what i have added?


 >> But also see here: ​https://docs.microsoft.com/en-
 us/windows/win32/api/dxva2api/ne-dxva2api-dxva2_videoprimaries BT.470-2
 System M; EBU 3212 (sic, non-existant 3212 spec, funny, should be 3213)

 Yeah indeed, https://docs.microsoft.com/en-us/windows/win32/api/dxva2api
 /ne-dxva2api-dxva2_videoprimaries seems to suggest it should be
 AVCOL_PRI_BT470M, not AVCOL_PRI_BT470BG. But lets assume the docs are
 wrong on that point too, besides what you pointed out?

 I have also added determination of color space, using VideoTransferMatrix,
 and falling back on a guess if VideoTransferMatrix is not known, but
 VideoPrimaries is.

 Lastly, the discovered info is now exposed through the stream's codecpars,
 so it can actually be used.

 Thanks for the help!
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Ticket URL: <https://trac.ffmpeg.org/ticket/9271#comment:4>
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