Readonlydurationhow long one pass over the frames takes, startTime excluded
Readonlyframethe duration every frame without one of its own is held for
ReadonlyframesReadonlyloopReadonlystartthe frame playing seconds in, with startTime and loop applied
Which frame plays seconds in. Before it starts the first frame is held, however long that
is, and a non-looping animation that has run out stays on its last frame rather than running
off the end.
Example