[FFmpeg-user] ffmpeg MP4/x264 output colours change when input source is different resolution (bug?)

[Michael Koch]

Am 15.09.2022 um 11:41 schrieb Paul B Mahol:
> On 9/15/22, Michael Koch <astroelectronic at t-online.de> wrote:
>> Am 15.09.2022 um 11:26 schrieb Dan:
>>>> You are right that datascope shows no difference. But the issue is also
>>>> reproducible with VLC player.
>>> As well as VLC Player and FFplay, I've tried MediaPlayerClassic,
>>> Google Chrome,
>>> Microsoft Edge and Vegas Pro, and the problem occurs with each of
>>> those. Could
>>> there be a "takes two to tango" thing going on, where both the players
>>> and ffmpeg
>>> are at fault due to miscommunication? It's somewhat hard to conceive
>>> they'd all
>>> interpret the file incorrectly otherwise. Only one player I tried -
>>> Irfanview - interpreted
>>> it correctly.
>>>
>>> I can't get to test it with Firefox or Waterfox unfortunately. They
>>> think the file
>>> is corrupt (output mp4 produced using the "-f lavfi -i
>>> color=0x19be0f:s=400x720" technique).
>>> Maybe there's a way around that.
>>>
>>> Also, showinfo produced an incorrect colour too. See:
>>> https://i.imgur.com/LF43udT.png
>>>
>>> (I use: "ffplay.exe -vf showinfo 576.mp4" ).
>>>
>>> In summary, I've love a workaround at least, or at least some
>>> reassurance that
>>> Chrome et al. will come round to fix this, or that ffmpeg will
>>> communicate the file
>>> better to them.
>> This seems to work with VLC player:
>>
>> ffmpeg -f lavfi -i color=0x19be0f:s=400x576 -colorspace bt709 -crf 0
>> -vcodec libx264 -t 5 -y out1.mp4
>> ffmpeg -f lavfi -i color=0x19be0f:s=400x578 -colorspace bt709 -crf 0
>> -vcodec libx264 -t 5 -y out2.mp4
> mostly because of extra -colorspace flag supplied.

Wouldn't it be a good idea to show in FFprobe a message 
"colorspace=unknown" if colorspace isn't set?