Working with transparent footage?

[Ampix0]

I have created a few 4K transitions and my Intro for my youtube video. Previously I directly imported the AE file, which made for incredibly slow playback making it hard to ensure the video is lined up properly. I wanted to export these files in 4K and 1080p for proxies. I'm having some issues exporting video with the alpha channel though. Various tutorials just seemed to fail. Lossless AVI I believe did work, but the file size is 2GB for 2 seconds of a transition.

Should I just continue working with the AE file? Does anyone have a better tutorial for exporting video with alpha?

[JPT7505]

Png sequence

[jsn951]

any 16/32 bit image sequence should do, just make sure you choose RGB + ALPHA. If you prefer a self-contained video vs an image sequence, you could use quicktime with png/tiff/targa preset and include alpha as well.