pcm/Export: halve the sample rate for DoP

src/output/plugins/AlsaOutputPlugin.cxx

@@ -666,7 +666,6 @@ AlsaOutput::SetupDop(const AudioFormat audio_format,
 
 	AudioFormat dop_format = audio_format;
 	dop_format.format = SampleFormat::S24_P32;
-	dop_format.sample_rate /= 2;
 
 	const AudioFormat check = dop_format;
 
@@ -698,11 +697,12 @@ AlsaOutput::SetupOrDop(AudioFormat &audio_format, PcmExport::Params &params)
 	std::exception_ptr dop_error;
 	if (dop && audio_format.format == SampleFormat::DSD) {
 		try {
-			SetupDop(audio_format, params);
 			params.dop = true;
+			SetupDop(audio_format, params);
 			return;
 		} catch (...) {
 			dop_error = std::current_exception();
+			params.dop = false;
 		}
 	}
 

src/pcm/PcmExport.cxx

@@ -106,6 +106,11 @@ PcmExport::Params::CalcOutputSampleRate(unsigned sample_rate) const
 		/* DSD_U32 combines four 8-bit "samples" in one 32-bit
 		   "sample" */
 		sample_rate /= 4;
+
+	if (dop)
+		/* DoP packs two 8-bit "samples" in one 24-bit
+		   "sample" */
+		sample_rate /= 2;
 #endif
 
 	return sample_rate;
@@ -117,6 +122,9 @@ PcmExport::Params::CalcInputSampleRate(unsigned sample_rate) const
 #ifdef ENABLE_DSD
 	if (dsd_u32)
 		sample_rate *= 4;
+
+	if (dop)
+		sample_rate *= 2;
 #endif
 
 	return sample_rate;

test/test_pcm_export.cxx

@@ -175,6 +175,9 @@ PcmExportTest::TestDop()
 	PcmExport::Params params;
 	params.dop = true;
 
+	CPPUNIT_ASSERT_EQUAL(params.CalcOutputSampleRate(705600u), 176400u);
+	CPPUNIT_ASSERT_EQUAL(params.CalcInputSampleRate(176400u), 705600u);
+
 	PcmExport e;
 	e.Open(SampleFormat::DSD, 2, params);