How to use APNG in OBS Studio (Deprecated)
Now APNG is properly supported in OBS without need of this mess, use Media source instead. Preveiw still doesn't show up but it will work on canvas.
Just add browser source, check local file and select APNG, then add !important in CSS at end of background-color property.
Baka me didn't know this and wasted ~6 hr over few days in ffmpeg and concat.