rsvgoverlay: allow dynamic images through data_sink
rsvgoverlay cannot render a sequence of more than one svg frame from its data_sink, while rsvgdec can.
rsvgoverlay waits for an EoF event before rendering a frame. This prevents stream sources from being able to trigger a push event, and once a push event has been triggered, it prevents the overlay from being updated.
This is fine for loading static images from filesrc, but that use-case is well-supported via the location property. Other bugs prevent live animations in rsvgdec from being easily composited over a video.
rsvgdec contains logic to look for
</svg> to trigger a push event, this can be replicated in rsvgoverlay. See this comment
Should I try to make a pull request?
edits: clarify this issue doesn't relate to svg animation features