[FFmpeg-user] Create a 10-bit VLog test video

[Mick Finn]

Does vlc use 10 bit or 8 bit build? Doubt it used 10bit

Sent from my iPhone

> On Sep 20, 2020, at 8:20 PM, Michael Koch <astroelectronic at t-online.de> wrote:
> 
> Am 19.09.2020 um 17:01 schrieb Paul B Mahol:
>>> On Sat, Sep 19, 2020 at 12:10 PM Michael Koch <astroelectronic at t-online.de>
>>> wrote:
>>> 
>>> Hello all,
>>> 
>>> I want to create a 10-bit VLog test video which contains 18 levels of
>>> gray, according to Panasonic's VLog curve.
>>> The curve is documented here:
>>> 
>>> https://pro-av.panasonic.net/en/cinema_camera_varicam_eva/support/pdf/VARICAM_V-Log_V-Gamut.pdf
>>> 
>>> I want the leftmost bar to be black (128) and the other 17 bars are for
>>> -8 to +8 stops, so that the rightmost bar is at level 1023. I'm using
>>> this command line and the console output is copied below:
>>> 
>>> ffmpeg -f lavfi -i nullsrc=s=svga,format=gray16 -lavfi
>>> geq=lum='st(0,trunc(18*X/W));64*(128*eq(ld(0),0)+132*eq(ld(0),1)+136*eq(ld(0),2)+144*eq(ld(0),3)+160*eq(ld(0),4)+192*eq(ld(0),5)+240*eq(ld(0),6)+298*eq(ld(0),7)+363*eq(ld(0),8)+433*eq(ld(0),9)+505*eq(ld(0),10)+578*eq(ld(0),11)+652*eq(ld(0),12)+726*eq(ld(0),13)+800*eq(ld(0),14)+874*eq(ld(0),15)+949*eq(ld(0),16)+1023*eq(ld(0),17))'
>>> 
>>> -pix_fmt yuv444p10le -crf 10 -c:v h264 -t 5 -y VLog_10bit.mov
>>> 
>>> The video looks perfect when played with FFplay. The leftmost bars are
>>> indistinguishable on a 8-bit monitor because the levels are too close
>>> together, but the rightmost bars look as expected.
>>> 
>>> However when I play the same video with VLC, the two brightest bars at
>>> the right side have the same shade of gray. I don't understand why. Is
>>> this a problem in my video, or is it a problem in VLC?
>>> 
>>> When I extraxt a 16-bit PNG image from the video, this looks as expected
>>> with 18 levels of gray.
>>> ffmpeg -i VLog_10bit.mov -frames 1 -y out.png
>>> 
>>> Unrelated: I did try to add the oscilloscope filter at the end of the
>>> filter chain, but it seems it doesn't work with 16-bit data. There
>>> should be a warning or an error message. oscilloscope=tw=1:s=1
>>> 
>> That happened only with gray>8 formats and have been fixed already.
> 
> Thanks, oscilloscope works fine now.
> Do you have any idea why the brightest bar looks correct in FFplay and wrong in VLC?
> Is the problem reproducible on other computers?
> 
> Michael
> 
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