TODO 
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- audio base classes:
   - GstBaseAudioSink
      - parse caps into rinbuffer spec, also make sure surround sound
        is parsed correctly.
      - implement seek/query/convert
      - implement getrange scheduling
   - simple resampling
   - more accurate master/slave calibration handling
   - faster audio cutoff when going to PAUSED
   - resubmit samples from ringbuffer when doing PAUSED->PLAYING again
   - the ringbuffer should have a state where it is filling up the
     buffer before going to playing.