I am struggling to find a solution for this as well. I was hoping a simple URL parameter would do the trick, but I haven't found one yet. I've tried the same ones you have, as well as things like "playPause", "animation", "play", "loop", "start", etc. And I've tried values of "1", "on", "true" for all of those. I guess it's just not supported.

I did see somewhere else that someone was able to send a javascript command to click the "playpause" button after loading. But I'm using iframe within my Home Assistant server and don't have the ability to pass javascript. :(