output/osx: improve sample rate selection

The formula in osx_output_score_sample_rate() to detect multiples of the source sample rate was broken: when given a 44.1 kHz input file, it preferred 16 kHz over 48 kHz, because its `frac_portion(16)=0.75` is smaller than `frac_portion(48)=0.91`. That formula, introduced by commit 40a1ebee, looks completely wrong. It doesn't do what the code comment pretends it does. Instead of using that `frac_portion` to calculate a score, this patch adds to the score only if `frac_portion` is nearly `0` or `1`. This means that the factor is nearly integer. Closes https://github.com/MusicPlayerDaemon/MPD/issues/904

output/osx: improve sample rate selection
691b6a23 · Max Kellermann · 5c7243d3 · 691b6a23 · 691b6a23
Commit 691b6a23 authored Jul 01, 2020 by Max Kellermann
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NEWS NEWS +2 -0

OSXOutputPlugin.cxx src/output/plugins/OSXOutputPlugin.cxx +2 -1

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--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,8 @@ ver 0.21.25 (not yet released)
 * input
  - file: detect premature end of file
  - smbclient: don't send credentials to MPD clients
+* output
+  - osx: improve sample rate selection
 * Windows/Android:
  - fix Boost detection after breaking change in Meson 0.54


--- a/src/output/plugins/OSXOutputPlugin.cxx
+++ b/src/output/plugins/OSXOutputPlugin.cxx
@@ -342,7 +342,8 @@ osx_output_score_sample_rate(Float64 destination_rate, unsigned source_rate)
 	double int_portion;
 	double frac_portion = modf(source_rate / destination_rate, &int_portion);
 	// prefer sample rates that are multiples of the source sample rate
-	score += (1 - frac_portion) * 1000;
+	if (frac_portion < 0.01 || frac_portion >= 0.99)
+		score += 1000;
 	// prefer exact matches over other multiples
 	score += (int_portion == 1.0) ? 500 : 0;
 	if (source_rate == destination_rate)