waveformview: show in/out points in waveformview

Moved drawing routines to the base class that is used by both TimeRuler
and WaveformView

app/render/audioparams.cpp

@@ -26,6 +26,11 @@ const uint64_t &AudioParams::channel_layout() const
   return channel_layout_;
 }
 
+rational AudioParams::time_base() const
+{
+  return rational(1, sample_rate());
+}
+
 AudioRenderingParams::AudioRenderingParams() :
   format_(SampleFormat::SAMPLE_FMT_INVALID)
 {

app/render/audioparams.h

@@ -14,6 +14,7 @@ public:
 
   const int& sample_rate() const;
   const uint64_t& channel_layout() const;
+  rational time_base() const;
 
 private:
   int sample_rate_;