[FFmpeg-user] ffmpeg makes some sources darker

[Jim Worrall]

> On 2016 Jan 5, at 8:38 AM, Andy Furniss <adf.lists at gmail.com> wrote:
> 
> Should be that, the png is a different issue/feature - I don't know
> what's correct or not. I guess you saw my other post that showed the
> gamma difference. Whether you see it or not is going to be down to the
> viewer/ICC/OS setup. I haven't got a clue which is correct - I mean we a
> re likely seeing 709 on an srgb monitor so not the same as a 709  TV -
> perhaps the "corrected" version is the correct one. Not that when
> playing the movie you would be using a png viewer anyway. What you get
> from players may be a bit pot luck! Even with the same player there can
> be differences between output types (xv,vdpau,opengl).
> 
> If you really want playback colour perfection, mpv can do correction
> using ICC profiles for different displays.
> _______________________________________________

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.