bin: set_state to PLAYING of non-toplevel bin might stop at PAUSED
Submitted by Mark Nauwelaerts
... particularly if NO_PREROLL element present in bin.
Since NO_PREROLL "eats" any ASYNC, occurrence of the former tends to trigger a "fake async-done" to counter the latter, see e.g. gst_bin_add_func when adding a NO_PREROLL element, or decodebin2 change_state function forcing async_done upon NO_PREROLL state change of bin.
In any case, bin_handle_async_done is triggered, which (silently) ignores further state change to PLAYING assuming that (some) parent will take care of it later on. While that is the case in "normal" state changes, it need not be so in more "advanced/dynamic" custom bin scenarios (decodebin2, etc etc), depending on whether parents already reached PLAYING earlier or other ASYNC_START are pending somewhere else. Specific cases are in e.g. bug 628214 or bug 632656.
As such, this may be intended behaviour, but it might need some tweaking or some warning/documentation indicating that a good old _set_state (..., PLAYING) needs some caution as it may "fail" silently and would have to be replaced by _set_state (..., PAUSED) followed by _set_state (..., PLAYING).