Why import will work only with some .mov files?

I have 2 .mov files 1. edited with Premeir and saved as .mov file 2. animation created in aftere effects, and rendered as .mov file with transparent background

I need to take file 2, with the transparent background and place it in Unity, but I get errors on import. Errors I don't get with the first file. Why can't unity read the transparent background file? It's a 8 seconds of animated movie. How can unity know to read one .mov but not the other? I've re-installed quicktime.

EDIT: I've rendered the animation in blender and turned it into h.264 file format. but unity will not let me turn h.264 format into video texture, and instead plays the animation on black background insteas of transparent one.