*: add explicit

src/filter/plugins/AutoConvertFilterPlugin.cxx

@@ -64,7 +64,7 @@ class PreparedAutoConvertFilter final : public PreparedFilter {
 	std::unique_ptr<PreparedFilter> filter;
 
 public:
-	PreparedAutoConvertFilter(std::unique_ptr<PreparedFilter> _filter) noexcept
+	explicit PreparedAutoConvertFilter(std::unique_ptr<PreparedFilter> _filter) noexcept
 		:filter(std::move(_filter)) {}
 
 	std::unique_ptr<Filter> Open(AudioFormat &af) override;

src/filter/plugins/ConvertFilterPlugin.cxx

@@ -42,7 +42,7 @@ class ConvertFilter final : public Filter {
 	std::unique_ptr<PcmConvert> state;
 
 public:
-	ConvertFilter(const AudioFormat &audio_format);
+	explicit ConvertFilter(const AudioFormat &audio_format);
 
 	void Set(const AudioFormat &_out_audio_format);
 

src/filter/plugins/NormalizeFilterPlugin.cxx

@@ -34,7 +34,7 @@ class NormalizeFilter final : public Filter {
 	PcmBuffer buffer;
 
 public:
-	NormalizeFilter(const AudioFormat &audio_format)
+	explicit NormalizeFilter(const AudioFormat &audio_format)
 		:Filter(audio_format), compressor(Compressor_new(0)) {
 	}
 

src/filter/plugins/RouteFilterPlugin.cxx

@@ -130,7 +130,7 @@ public:
 	 * @param block the configuration block to read
 	 * @param filter a route_filter whose min_channels and sources[] to set
 	 */
-	PreparedRouteFilter(const ConfigBlock &block);
+	explicit PreparedRouteFilter(const ConfigBlock &block);
 
 	/* virtual methods from class PreparedFilter */
 	std::unique_ptr<Filter> Open(AudioFormat &af) override;