Merge remote-tracking branch 'cus/stable'

* cus/stable:
  ffplay: use libswresample instead of av_audio_convert
  audioconvert: add av_get_default_channel_layout public function
  ffplay: use avctx->channels and avctx->freq before avcodec_open2 consistently
  ffplay: remove now unnecessary request_channels, we set it now with options
  ffplay: set request_channels to 2

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