Simplify and test audio sample rate alteration.

2 files changed, 29 insertions, 10 deletions

diff --git a/src/lib/film_state.cc b/src/lib/film_state.cc
index 3cd7091ca..3d58a4fec 100644
--- a/src/lib/film_state.cc
+++ b/src/lib/film_state.cc
@@ -283,18 +283,14 @@ FilmState::bytes_per_sample () const
 int
 FilmState::target_sample_rate () const
 {
+	/* Resample to a DCI-approved sample rate */
 	double t = dcp_audio_sample_rate (audio_sample_rate);
+
+	/* Compensate for the fact that video will be rounded to the
+	   nearest integer number of frames per second.
+	*/
 	if (rint (frames_per_second) != frames_per_second) {
-		if (fabs (frames_per_second - 23.976) < 1e-6 || (fabs (frames_per_second - 29.97) < 1e-6)) {
-			/* 24fps or 30fps drop-frame ie {24,30} * 1000 / 1001 frames per second;
-			   hence we need to resample the audio to dcp_audio_sample_rate * 1000 / 1001
-			   so that when we play it back at dcp_audio_sample_rate it is sped up
-			   by the same amount that the video is
-			*/
-			t *= double(1000) / 1001;
-		} else {
-			throw EncodeError ("unknown fractional frame rate");
-		}
+		t *= frames_per_second / rint (frames_per_second);
 	}
 
 	return rint (t);
diff --git a/test/test.cc b/test/test.cc
index ebee50ac0..d978d36a0 100644
--- a/test/test.cc
+++ b/test/test.cc
@@ -362,3 +362,26 @@ BOOST_AUTO_TEST_CASE (make_dcp_with_range_test)
 
 	BOOST_CHECK_EQUAL (JobManager::instance()->errors(), false);
 }
+
+BOOST_AUTO_TEST_CASE (audio_sampling_rate_test)
+{
+	FilmState fs;
+	fs.frames_per_second = 24;
+
+	fs.audio_sample_rate = 48000;
+	BOOST_CHECK_EQUAL (fs.target_sample_rate(), 48000);
+
+	fs.audio_sample_rate = 44100;
+	BOOST_CHECK_EQUAL (fs.target_sample_rate(), 48000);
+
+	fs.audio_sample_rate = 80000;
+	BOOST_CHECK_EQUAL (fs.target_sample_rate(), 96000);
+
+	fs.frames_per_second = 23.976;
+	fs.audio_sample_rate = 48000;
+	BOOST_CHECK_EQUAL (fs.target_sample_rate(), 47952);
+
+	fs.frames_per_second = 29.97;
+	fs.audio_sample_rate = 48000;
+	BOOST_CHECK_EQUAL (fs.target_sample_rate(), 47952);
+}