[FFmpeg-trac] #4805(undetermined:new): swscale does not process pixels when only color-matrix differs between input and output

[FFmpeg]

#4805: swscale does not process pixels when only color-matrix differs between
input and output
-------------------------------------+-------------------------------------
             Reporter:  rmk          |                     Type:
               Status:  new          |  enhancement
            Component:               |                 Priority:  normal
  undetermined                       |                  Version:
             Keywords:               |  unspecified
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
-------------------------------------+-------------------------------------
 swscale does not seem to process pixels when only color-matrix differs
 between input and output (i.e. pixel format and size remain the same).

 It would be great to be able to use swscale also just for colorspace
 transformations like for bt601<->bt709 conversions.

 Observed this as api user but verified it by converting two files as
 follows and comparing them via framemd5:

 ffmpeg -i fcp7_xdcam_ex_1080_25p_1s.mov -vf
 scale=in_color_matrix=bt709:out_color_matrix=bt601 -c:v ffv1 -an
 scale_test_bt601.nut
 ffmpeg -i xdcam_ex/fcp7_xdcam_ex_1080_25p_1s.mov -c:v ffv1 -an
 scale_test_unscaled.nut

 The frames of the resulting files are identical.

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Ticket URL: <https://trac.ffmpeg.org/ticket/4805>
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