[FFmpeg-user] Color Channel Expression

[Jon bae]

2017-07-31 10:30 GMT+02:00 Paul B Mahol <onemda at gmail.com>:
>
>>
>> What exactly you tried?
>>
>> Perhaps you want premultiply filter?
>>
>> Yes I have a video and a lower third, and I want to overlay the lower
> third. But my alpha channel from the lower third is not pre-devided with
> the alpha channel, so  I need to do a channel division in ffmpeg.
> Something like:
>
> ffmpeg -i video.mp4 -i lowerthird.png -filter_complex
> [1:v]geq=r=r/a:g=g/a:b=b/a[gq];[0:v][gq]overlay ... output.mp4
>
> I see that you wrote a filter for this, but can you please give me an
example of how it works? I don't get it to run.