I just discovered you can work with transparent video
on LumaFusion without the need for workarounds like chroma key. Apparently, HEVC codec allows for an alpha channel, so I tried getting my hands on some video with a transparent background to see if it works on LumaFusion. [SPOILER] It did!
ProRes 4444 is vastly known for its alpha channel capabilities but it's quite a heavy codec for most uses and it doesn't work on iOS or iPadOS. Turns out that you can convert from ProRes 4444 to HEVC right from the Finder in macOS Catalina. You should right-click the transparent ProRes 4444 file, got to 'Services', and then 'Encode Selected Video Files'. If you've done this before, you may know that this pops up a window with options for converting your footage into various resolutions and codecs, including Audio Only. In macOS Catalina, you'll find that you can convert to HEVC 1080p and 2160p, with the option to preserve transparency.
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After it's converted, I imported the file into my iPad and now I have perfectly working transparent video. It's also waaaay lighter than ProRes 4444. In the file I've tested, the ProRes 4444 was 37,2 MB, and the HEVC one was only 323 KB.
This is very useful especially if you work with lots of motion graphics on your videos, though I've found that even if you export the transparent HEVC file on LumaFusion, it won't work, and I haven't found any other app to do so right on the iPad which is a shame. I would love it if LumaFusion would add the ability to export HEVC files with transparency.
Anyway, I don't know if this was talked before in the forum but I hope it helps everyone who doesn't know about this.