Jim Worrall wrote:
On 2016 Jan 4, at 1:33 PM, Carl Eugen Hoyos <[email protected]>
wrote:
How did you produce the screenshots?
ffmpeg -i in.mkv -vf fps=1/6 %03din.png
I do see that one of the png files you uploaded is lighter but when
I look at the 91st frame of the file you uploaded, it is darker
here with MPlayer, vlc and FFplay (and when I transcode it).
Or to say it differently: How do you know it is supposed to be
lighter?
Sorry, I don’t quite understand. The screenshots from the source are
brighter than those from the transcode. That’s why I think the
transcode should be brighter.
The video I uploaded is the source - the bright one - so if it looks
darker to you than the bright png, maybe I’m doing something wrong.
I think it's because the master is flagged as rec709 but the yuv and I
guess hevc aren't.
Some players (not mplayer) would assume 709 for >= 720p so you wouldn't
notice with them.
It seems ffmpeg swscale/png honors the 709 for the master.
testing -
ffmpeg -i in.mkv -vframes 1 frame1-master.png
ffmpeg -i in.mkv -vframes 1 -vcodec rawvideo -f rawvideo frame1-master.yuv
ffmpeg -f rawvideo -pix_fmt yuv420p -s 1920x1080 -i frame1-master.yuv
frame1-yuv.png
and frame1-yuv.png is darker than frame1-master.png
do
ffmpeg -f rawvideo -pix_fmt yuv420p -s 1920x1080 -i frame1-master.yuv
-vf scale=in_color_matrix=bt709 frame1-yuv-709.png
and frame1-yuv-709.png visually (but not md5sum) matches frame1-master.png
so I guess you need to tell hevc that the video is rec709.
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