How to preserve the alpha channel with After Effects
Work with your background-less Rotato renders in After Effects
Rotato is a great shortcut for working with 3D mockups in After Effects. Most often, you'll want to add your device mockups on top of other elements in your video, so exporting from Rotato with an alpha channel is the way to go. But since After Effects still doesn't support HEVC With Alpha, it's not as smooth as you might think.
How to do it
First, export your 3D rendering from Rotato as HEVC With Alpha.
If you're not on macOS 12.1
If you're not on macOS 12.1, you can now right click on your exported
mov in Finder, choose Encode Selected Video Files, then ProRes, and check Preserve transparency.
If you're on macOS 12.1
In macOS 12.1 however, there's a bug that causes a weird error message, and this method won't work. As a workaround, you can do this in Terminal
avconvert --source path/to/hevc-with-alpha.mp4 --preset PresetAppleProRes4444LPCM --output path/to/prores-with-alpha.mov
This will convert the HEVC file to a ProRes4444 format that Adobe After Effects understands. You can now drag in the resulting ProRes file to After Effects and enjoy the alpha channel