ffmpeg – combine pngs images with transparency into a video and merge it on a static image

I’m trying to combine multiple png frames into a video with ffmpeg, keeping the transparency, to then combine it with an image. The png video comes with a black background so when i try to combine it with an image, the image is completely overlayed by the black background, how can I keep the transparency?

Here’s the command I use to combine the PNGs:

ffmpeg -y -i src/tmp/%d.png -c:v libx264 -vf fps=25 -pix_fmt yuva420p land.mov

I already tried also with ffmpeg -y -i src/tmp/%d.png -c copy land.mov as suggested by another user but the video is corrupted