Opacity animation not rendering corectly with transparent background

Hi, I've been trying for a while to get this to work but to no avail. I need to render some videos with an animation and a transparent background, which works just fine, but the problem comes in when the final video doesn't show the animated opacity on the elements inside. How do I get the opacity to render properly but keep the transparent bg on the final video? PS: In After Effects and if not rendered with transparent bg the opacity works just fine.