Web animation with alpha channel

This is probably old now, but I have started (once again) to look at embedding an animation with an alpha channel (transparency) into a web page. I really need to use the PNG format, but need something that is cross-platform, mobile, and friendly in the absence of JavaScript.

I had previously reviewed the use of MNG and APNG but hit cross-platform issues. Web searches revealed nothing at all. So, with a stab in the dark, I investigated if CSS could help in some way. This page came up where a responder created an example here. It uses JavaScript timers to move the viewport on an image that has been constructed like cinema film.