[FFmpeg-user] Remove everything but a single color (range)

[Hans Carlson]

On Wed, 18 Mar 2020, Carl Eugen Hoyos wrote:

> Am Di., 17. März 2020 um 00:38 Uhr schrieb Hans Carlson <forbyta at gmx.com>:
>>
>> Can anyone explain to me why this displays only the yellow bar with
>> everything else black:
>>
>>    ffplay -f lavfi -i 'smptehdbars=duration=5' -vf "colorhold=color=0xbcc906:similarity=0.25,chromakey=color=black:similarity=.2"
>>
>> but this displays all bars in gray scale except the yellow bar which is
>> in color:
>>
>>    ffmpeg -f lavfi -i 'smptehdbars=duration=5' -vf "colorhold=color=0xbcc906:similarity=0.25,chromakey=color=black:similarity=.2" TEST-smptehdbars-yellow-only.mkv
>>
>> What I want is ONLY the yellow bar and everything else black, as in the
>> ffplay command.  How can I get the same thing with ffmpeg?
>
> You need to also use the overlay filter.

Can you expand on that a bit?  What am I overlaying?  I only have one 
input.

And why does the above command work using ffplay, but not ffmpeg?