Using ImageMagick on the command line I can use the composite and compose options to use one image to replace the alpha mask of another image. Is this possible using transloadit ? I see an option to add a watermark but nothing related to replacing the alpha channel.
That's currently not possible. I'm a Transloadit cofounder though and if you can email us about your usecase, timeframe, and expected volume, we might be able to implement this for you.