[FFmpeg-user] ffmpeg makes some sources darker

[Andy Furniss]

Jim Worrall wrote:
>>
>> 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.
>
> Yes.  The ORIGINAL source file gives
> Stream #0:0(eng): Video: h264 (High), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc
>
> The transcode with the x265-params gives
> Stream #0:0(eng): Video: hevc (Main), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn, 23.98 tbc (default)
>
> Could the problem be that the input is not recognized as bt709, even though it is?

Yes, that's probably it.

Maybe you could try below to see if the original shows 709 -

ffmpeg -analyzeduration 100M -probesize 100M -i original.m2ts

FWIW I just noticed another issue - using pass 1 and pass 2 via ffmpeg 
doesn't work for libx265.

It does work if you use it via -x265-params pass=