decklinkaudiosink: Re-implement around GstBaseSink instead of GstAudioBaseSink

The Decklink and GstAudioBaseSink APIs don't fit very well together,
which causes various problems due to inaccuracies in the clock
calculations and the actual ringbuffer and GStreamer's copy getting of
sync.

Problems are audio drop-outs and A/V sync getting wrong after
pausing/seeking.

https://bugzilla.gnome.org/show_bug.cgi?id=790114
6 files changed