filter/Convert: add convert_filter_prepare()

src/filter/plugins/ConvertFilterPlugin.cxx

@@ -132,6 +132,12 @@ const FilterPlugin convert_filter_plugin = {
 	convert_filter_init,
 };
 
+PreparedFilter *
+convert_filter_prepare() noexcept
+{
+	return new PreparedConvertFilter();
+}
+
 Filter *
 convert_filter_new(const AudioFormat in_audio_format,
 		   const AudioFormat out_audio_format)

src/filter/plugins/ConvertFilterPlugin.hxx

@@ -20,9 +20,13 @@
 #ifndef MPD_CONVERT_FILTER_PLUGIN_HXX
 #define MPD_CONVERT_FILTER_PLUGIN_HXX
 
+class PreparedFilter;
 class Filter;
 struct AudioFormat;
 
+PreparedFilter *
+convert_filter_prepare() noexcept;
+
 Filter *
 convert_filter_new(AudioFormat in_audio_format,
 		   AudioFormat out_audio_format);

src/output/Init.cxx

@@ -31,6 +31,7 @@
 #include "filter/FilterPlugin.hxx"
 #include "filter/FilterRegistry.hxx"
 #include "filter/plugins/AutoConvertFilterPlugin.hxx"
+#include "filter/plugins/ConvertFilterPlugin.hxx"
 #include "filter/plugins/ReplayGainFilterPlugin.hxx"
 #include "filter/plugins/ChainFilterPlugin.hxx"
 #include "filter/plugins/VolumeFilterPlugin.hxx"
@@ -249,11 +250,8 @@ AudioOutput::Setup(EventLoop &event_loop,
 
 	/* the "convert" filter must be the last one in the chain */
 
-	auto *f = filter_new(&convert_filter_plugin, ConfigBlock());
-	assert(f != nullptr);
-
 	filter_chain_append(*prepared_filter, "convert",
-			    convert_filter.Set(f));
+			    convert_filter.Set(convert_filter_prepare()));
 }
 
 AudioOutput *