[FFmpeg-user] Color Channel Expression

[Paul B Mahol]

On 7/31/17, Jon bae <jonbae77 at gmail.com> wrote:
> 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.

"I don't get it to run" means nothing to me.