[FFmpeg-user] ffmpeg makes some sources darker

[Andy Furniss]

Jim Worrall wrote:
>> I’m not really looking for perfection, just don’t want the transcodes to be
>> darker on any device.
>>
>> So my testing has shown, for both libx264 and libx265, the problem is
>> solved (meaning the pngs come out with the same luminosity, which
>> is good enough for me) either of two ways, using ffmpeg options:
>>
>> -color_primaries bt709 -color_trc bt709 -colorspace bt709
>>
>> or using x264/5 params:
>>
>> -x264-params colormatrix=bt709:colorprim=bt709:transfer=bt709
>>
>> These alternatives are not quite parallel, I know.  Frankly I don’t
>> really understand them.  I’m guessing colormatrix is the only one
>> needed but haven’t tested.  In any case, it seems ffmpeg or libx26* needs
>> this direction.
>>
> Well I’m really confused now.  When I went back to the full source
> file (rather than the 1 minute clipped from  it, which was a
> stream copy), the transcode with x265-params came out BRIGHTER
> than the source.  My head’s about to explode.  I’m just going
> to stick with this result.

Ouch, did the new file show as 709 with

ffmpeg -i newfile.mkv

I can't reproduce this one myself x265-params seems to work.
If for some reason the newfile didn't get flagged as 709 then it could 
be possible to get brighter with different colours in a scene.