[FFmpeg-user] Hello. Gurus. Regarding PNG image overlay with alpha transparency change

[Paul B Mahol]

On Fri, Jun 7, 2024 at 5:55 AM Lee Mitchell <npdmailing at gmail.com> wrote:

> Hi.
>
> What I know is alpha change for another video clip pon base video like as
> "-filter_complex
> "[1:v]geq=r='r(X,Y)':a='if(between(t,0,9),alpha(X,Y)*(T/9),0)'[alpha];"
> which works very well as time goes by.
>
> But it is not working for a PNG image file as time goes by. It only sets
> alpha when the overlay starts which does not change while playing.
> How to change PNG alpha by base video clip's time?
> Could you guys advise me or hint me on keywords?
>

If you do not -loop single PNG, I think it will always have same time/PTS.
Use -loop 1 or loop video filter (faster processing, no need for decoding
same image all the time) instead, that one will ensure that time/PTS always
increases monotonically for that specific single PNG image.


>
> Thank you in advance.
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