FFMPEG prores_ks 4444 color shift I am attempting to encode "ProRes 4444" movies with ffmpeg.  Some research led me to the "prores_ks" encoder, which is the only one of ffmpeg's prores encoders that supports "4444".

I used this command to test it out (input excluded):

-c:v prores_ks -f mov -profile:v 4444 test.mov


This produces a ProRes 4444 movie.  However, the colors appear darker than the original input.  After some research I came upon this option:

-vf colormatrix=bt601:bt709


Adding this filter seems to fix the problem.  However, the file size is for some reason considerably bigger.  Also, I do not like the idea that a filter has to be performed during this encoding, as I want the highest possible quality.  Does anyone know of a way to overcome this "color shift" without a video filter?
I believe the problem lies in how FFMPEG does the RGB->YUV conversion by default.  This option specifies the use of the bt709 color space for the conversion, instead of the default of bt601.  This fixes it for me - though please let me know if I'm doing something bad here!

-vf scale=out_color_matrix=bt709