Merge remote-tracking branch 'cigaes/master'

* cigaes/master:
  lavfi/avf_showspectrum: check RDFT context init.
  lavfi/avf_showspectrum: add full frame sliding mode.
  lavfi/avf_showspectrum: use automatic framing.
  lavfi/avf_showspectrum: do not push the frame at EOF.
  lavfi/avf_showspectrum: fix output pts computation.
  lavfi/avf_showspectrum: set output frame rate.

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