Great question. So you're limited by the 5 or so frames you have at maximum. I would just put the png in a html page that auto-refreshes every second. And then a bit of javascript for the controls. But at that points it's more doom on HTML5 than png doom ...

No need to refresh, you can use multipart/x-mixed-replace to keep serving new images forever over the same HTTP request. This is not specific to PNG though.