Merge remote-tracking branch 'cus/stable'

* cus/stable:
  ffplay: decrease audio_diff_threshold
  ffplay: decrease max audio callbacks per second
  ffplay: calculate SDL audio buffer size based on sample rate
  ffplay: pass simple integers to calculate_display_rect and set_default_window_size
  ffplay: eliminate pictq_prev_picture

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