Merge remote-tracking branch 'cus/stable'

* cus/stable:
  ffplay: dump format before selecting streams
  ffplay: add support for stream specifiers in -ast, -vst, -sst options
  ffplay: remove unused no_background from videostate
  ffplay: remove flushed state from decoder context

Merged-by: Michael Niedermayer <michaelni@gmx.at>