audio: use sample rate rather than timebase now they aren't interchangeable

app/render/audioparams.cpp

@@ -105,7 +105,7 @@ qint64 AudioParams::time_to_samples(const double &time) const
 
   // NOTE: Not sure if we should round or ceil, but I've gotten better results with ceil.
   //       Specifically, we seem to occasionally get straggler ranges that never cache with round.
-  return qCeil(time_base().flipped().toDouble() * time);
+  return qCeil(double(sample_rate()) * time);
 }
 
 qint64 AudioParams::time_to_samples(const rational &time) const
@@ -122,7 +122,7 @@ qint64 AudioParams::samples_to_bytes(const qint64 &samples) const
 
 rational AudioParams::samples_to_time(const qint64 &samples) const
 {
-  return time_base() * samples;
+  return sample_rate_as_time_base() * samples;
 }
 
 qint64 AudioParams::bytes_to_samples(const qint64 &bytes) const