20 files changed, 538 insertions, 158 deletions

diff --git a/src/filter/FilterConfig.cxx b/src/filter/FilterConfig.cxx
new file mode 100644
index 000000000..d8c1fc6c2
--- /dev/null
+++ b/src/filter/FilterConfig.cxx
@@ -0,0 +1,80 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "FilterConfig.hxx"
+#include "plugins/ChainFilterPlugin.hxx"
+#include "FilterPlugin.hxx"
+#include "config/ConfigData.hxx"
+#include "config/ConfigOption.hxx"
+#include "config/ConfigGlobal.hxx"
+#include "config/ConfigError.hxx"
+#include "util/Error.hxx"
+
+#include <algorithm>
+
+#include <string.h>
+
+static bool
+filter_chain_append_new(Filter &chain, const char *template_name, Error &error)
+{
+	const struct config_param *cfg =
+		config_find_block(CONF_AUDIO_FILTER, "name", template_name);
+	if (cfg == nullptr) {
+		error.Format(config_domain,
+			     "filter template not found: %s",
+			     template_name);
+		return false;
+	}
+
+	// Instantiate one of those filter plugins with the template name as a hint
+	Filter *f = filter_configured_new(*cfg, error);
+	if (f == nullptr)
+		// The error has already been set, just stop.
+		return false;
+
+	const char *plugin_name = cfg->GetBlockValue("plugin",
+						     "unknown");
+	filter_chain_append(chain, plugin_name, f);
+
+	return true;
+}
+
+bool
+filter_chain_parse(Filter &chain, const char *spec, Error &error)
+{
+	const char *const end = spec + strlen(spec);
+
+	while (true) {
+		const char *comma = std::find(spec, end, ',');
+		if (comma > spec) {
+			const std::string name(spec, comma);
+			if (!filter_chain_append_new(chain, name.c_str(),
+						     error))
+				return false;
+		}
+
+		if (comma == end)
+			break;
+
+		spec = comma + 1;
+	}
+
+	return true;
+}
diff --git a/src/filter/FilterConfig.hxx b/src/filter/FilterConfig.hxx
new file mode 100644
index 000000000..1018eed51
--- /dev/null
+++ b/src/filter/FilterConfig.hxx
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/** \file
+ *
+ * Utility functions for filter configuration
+ */
+
+#ifndef MPD_FILTER_CONFIG_HXX
+#define MPD_FILTER_CONFIG_HXX
+
+class Filter;
+class Error;
+
+/**
+ * Builds a filter chain from a configuration string on the form
+ * "name1, name2, name3, ..." by looking up each name among the
+ * configured filter sections.
+ * @param chain the chain to append filters on
+ * @param spec the filter chain specification
+ * @param error_r space to return an error description
+ * @return true on success
+ */
+bool
+filter_chain_parse(Filter &chain, const char *spec, Error &error);
+
+#endif
diff --git a/src/filter/FilterInternal.hxx b/src/filter/FilterInternal.hxx
new file mode 100644
index 000000000..131c3b3f5
--- /dev/null
+++ b/src/filter/FilterInternal.hxx
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/** \file
+ *
+ * Internal stuff for the filter core and filter plugins.
+ */
+
+#ifndef MPD_FILTER_INTERNAL_HXX
+#define MPD_FILTER_INTERNAL_HXX
+
+#include <stddef.h>
+
+struct AudioFormat;
+class Error;
+
+class Filter {
+public:
+	virtual ~Filter() {}
+
+	/**
+	 * Opens the filter, preparing it for FilterPCM().
+	 *
+	 * @param filter the filter object
+	 * @param audio_format the audio format of incoming data; the
+	 * plugin may modify the object to enforce another input
+	 * format
+	 * @param error location to store the error occurring, or nullptr
+	 * to ignore errors.
+	 * @return the format of outgoing data or
+	 * AudioFormat::Undefined() on error
+	 */
+	virtual AudioFormat Open(AudioFormat &af, Error &error) = 0;
+
+	/**
+	 * Closes the filter.  After that, you may call Open() again.
+	 */
+	virtual void Close() = 0;
+
+	/**
+	 * Filters a block of PCM data.
+	 *
+	 * @param filter the filter object
+	 * @param src the input buffer
+	 * @param src_size the size of #src_buffer in bytes
+	 * @param dest_size_r the size of the returned buffer
+	 * @param error location to store the error occurring, or nullptr
+	 * to ignore errors.
+	 * @return the destination buffer on success (will be
+	 * invalidated by filter_close() or filter_filter()), nullptr on
+	 * error
+	 */
+	virtual const void *FilterPCM(const void *src, size_t src_size,
+				      size_t *dest_size_r,
+				      Error &error) = 0;
+};
+
+#endif
diff --git a/src/filter/FilterPlugin.cxx b/src/filter/FilterPlugin.cxx
new file mode 100644
index 000000000..98314f771
--- /dev/null
+++ b/src/filter/FilterPlugin.cxx
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "FilterPlugin.hxx"
+#include "FilterRegistry.hxx"
+#include "config/ConfigData.hxx"
+#include "config/ConfigError.hxx"
+#include "util/Error.hxx"
+
+#include <assert.h>
+
+Filter *
+filter_new(const struct filter_plugin *plugin,
+	   const config_param &param, Error &error)
+{
+	assert(plugin != nullptr);
+	assert(!error.IsDefined());
+
+	return plugin->init(param, error);
+}
+
+Filter *
+filter_configured_new(const config_param &param, Error &error)
+{
+	assert(!error.IsDefined());
+
+	const char *plugin_name = param.GetBlockValue("plugin");
+	if (plugin_name == nullptr) {
+		error.Set(config_domain, "No filter plugin specified");
+		return nullptr;
+	}
+
+	const filter_plugin *plugin = filter_plugin_by_name(plugin_name);
+	if (plugin == nullptr) {
+		error.Format(config_domain,
+			     "No such filter plugin: %s", plugin_name);
+		return nullptr;
+	}
+
+	return filter_new(plugin, param, error);
+}
diff --git a/src/filter/FilterPlugin.hxx b/src/filter/FilterPlugin.hxx
new file mode 100644
index 000000000..443d29881
--- /dev/null
+++ b/src/filter/FilterPlugin.hxx
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/** \file
+ *
+ * This header declares the filter_plugin class.  It describes a
+ * plugin API for objects which filter raw PCM data.
+ */
+
+#ifndef MPD_FILTER_PLUGIN_HXX
+#define MPD_FILTER_PLUGIN_HXX
+
+struct config_param;
+class Filter;
+class Error;
+
+struct filter_plugin {
+	const char *name;
+
+	/**
+         * Allocates and configures a filter.
+	 */
+	Filter *(*init)(const config_param &param, Error &error);
+};
+
+/**
+ * Creates a new instance of the specified filter plugin.
+ *
+ * @param plugin the filter plugin
+ * @param param optional configuration section
+ * @param error location to store the error occurring, or nullptr to
+ * ignore errors.
+ * @return a new filter object, or nullptr on error
+ */
+Filter *
+filter_new(const struct filter_plugin *plugin,
+	   const config_param &param, Error &error);
+
+/**
+ * Creates a new filter, loads configuration and the plugin name from
+ * the specified configuration section.
+ *
+ * @param param the configuration section
+ * @param error location to store the error occurring, or nullptr to
+ * ignore errors.
+ * @return a new filter object, or nullptr on error
+ */
+Filter *
+filter_configured_new(const config_param &param, Error &error);
+
+#endif
diff --git a/src/filter/FilterRegistry.cxx b/src/filter/FilterRegistry.cxx
new file mode 100644
index 000000000..286fb8db3
--- /dev/null
+++ b/src/filter/FilterRegistry.cxx
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "FilterRegistry.hxx"
+#include "FilterPlugin.hxx"
+
+#include <string.h>
+
+const struct filter_plugin *const filter_plugins[] = {
+	&null_filter_plugin,
+	&route_filter_plugin,
+	&normalize_filter_plugin,
+	&volume_filter_plugin,
+	&replay_gain_filter_plugin,
+	nullptr,
+};
+
+const struct filter_plugin *
+filter_plugin_by_name(const char *name)
+{
+	for (unsigned i = 0; filter_plugins[i] != nullptr; ++i)
+		if (strcmp(filter_plugins[i]->name, name) == 0)
+			return filter_plugins[i];
+
+	return nullptr;
+}
diff --git a/src/filter/FilterRegistry.hxx b/src/filter/FilterRegistry.hxx
new file mode 100644
index 000000000..24618a87a
--- /dev/null
+++ b/src/filter/FilterRegistry.hxx
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/** \file
+ *
+ * This library manages all filter plugins which are enabled at
+ * compile time.
+ */
+
+#ifndef MPD_FILTER_REGISTRY_HXX
+#define MPD_FILTER_REGISTRY_HXX
+
+#include "Compiler.h"
+
+extern const struct filter_plugin null_filter_plugin;
+extern const struct filter_plugin chain_filter_plugin;
+extern const struct filter_plugin convert_filter_plugin;
+extern const struct filter_plugin route_filter_plugin;
+extern const struct filter_plugin normalize_filter_plugin;
+extern const struct filter_plugin volume_filter_plugin;
+extern const struct filter_plugin replay_gain_filter_plugin;
+
+gcc_pure
+const struct filter_plugin *
+filter_plugin_by_name(const char *name);
+
+#endif
diff --git a/src/filter/AutoConvertFilterPlugin.cxx b/src/filter/plugins/AutoConvertFilterPlugin.cxx
index 918a16e53..cdeeefdc6 100644
--- a/src/filter/AutoConvertFilterPlugin.cxx
+++ b/src/filter/plugins/AutoConvertFilterPlugin.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -20,11 +20,11 @@
 #include "config.h"
 #include "AutoConvertFilterPlugin.hxx"
 #include "ConvertFilterPlugin.hxx"
-#include "FilterPlugin.hxx"
-#include "FilterInternal.hxx"
-#include "FilterRegistry.hxx"
+#include "filter/FilterPlugin.hxx"
+#include "filter/FilterInternal.hxx"
+#include "filter/FilterRegistry.hxx"
 #include "AudioFormat.hxx"
-#include "ConfigData.hxx"
+#include "config/ConfigData.hxx"
 
 #include <assert.h>
 
@@ -88,7 +88,11 @@ AutoConvertFilter::Open(AudioFormat &in_audio_format, Error &error)
 
 		assert(audio_format2 == in_audio_format);
 
-		convert_filter_set(convert, child_audio_format);
+		if (!convert_filter_set(convert, child_audio_format, error)) {
+			delete convert;
+			filter->Close();
+			return AudioFormat::Undefined();
+		}
 	} else
 		/* no */
 		convert = nullptr;
diff --git a/src/filter/AutoConvertFilterPlugin.hxx b/src/filter/plugins/AutoConvertFilterPlugin.hxx
index 7db72a345..c5dfdd2f6 100644
--- a/src/filter/AutoConvertFilterPlugin.hxx
+++ b/src/filter/plugins/AutoConvertFilterPlugin.hxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
diff --git a/src/filter/ChainFilterPlugin.cxx b/src/filter/plugins/ChainFilterPlugin.cxx
index cb52b86ca..7dc6db667 100644
--- a/src/filter/ChainFilterPlugin.cxx
+++ b/src/filter/plugins/ChainFilterPlugin.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -19,9 +19,9 @@
 
 #include "config.h"
 #include "ChainFilterPlugin.hxx"
-#include "FilterPlugin.hxx"
-#include "FilterInternal.hxx"
-#include "FilterRegistry.hxx"
+#include "filter/FilterPlugin.hxx"
+#include "filter/FilterInternal.hxx"
+#include "filter/FilterRegistry.hxx"
 #include "AudioFormat.hxx"
 #include "util/Error.hxx"
 #include "util/Domain.hxx"
diff --git a/src/filter/ChainFilterPlugin.hxx b/src/filter/plugins/ChainFilterPlugin.hxx
index 884c7ca19..b36aa3322 100644
--- a/src/filter/ChainFilterPlugin.hxx
+++ b/src/filter/plugins/ChainFilterPlugin.hxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
diff --git a/src/filter/ConvertFilterPlugin.cxx b/src/filter/plugins/ConvertFilterPlugin.cxx
index 040f8426f..27e6774f8 100644
--- a/src/filter/ConvertFilterPlugin.cxx
+++ b/src/filter/plugins/ConvertFilterPlugin.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -19,16 +19,15 @@
 
 #include "config.h"
 #include "ConvertFilterPlugin.hxx"
-#include "FilterPlugin.hxx"
-#include "FilterInternal.hxx"
-#include "FilterRegistry.hxx"
+#include "filter/FilterPlugin.hxx"
+#include "filter/FilterInternal.hxx"
+#include "filter/FilterRegistry.hxx"
 #include "pcm/PcmConvert.hxx"
 #include "util/Manual.hxx"
 #include "AudioFormat.hxx"
 #include "poison.h"
 
 #include <assert.h>
-#include <string.h>
 
 class ConvertFilter final : public Filter {
 	/**
@@ -39,21 +38,18 @@ class ConvertFilter final : public Filter {
 
 	/**
 	 * The output audio format; the consumer of this plugin
-	 * expects PCM data in this format.  This defaults to
-	 * #in_audio_format, and can be set with convert_filter_set().
+	 * expects PCM data in this format.
+	 *
+	 * If this is AudioFormat::Undefined(), then the #PcmConvert
+	 * attribute is not open.  This can mean that Set() has failed
+	 * or that no conversion is necessary.
 	 */
 	AudioFormat out_audio_format;
 
 	Manual<PcmConvert> state;
 
 public:
-	void Set(const AudioFormat &_out_audio_format) {
-		assert(in_audio_format.IsValid());
-		assert(out_audio_format.IsValid());
-		assert(_out_audio_format.IsValid());
-
-		out_audio_format = _out_audio_format;
-	}
+	bool Set(const AudioFormat &_out_audio_format, Error &error);
 
 	virtual AudioFormat Open(AudioFormat &af, Error &error) override;
 	virtual void Close() override;
@@ -69,12 +65,40 @@ convert_filter_init(gcc_unused const config_param &param,
 	return new ConvertFilter();
 }
 
+bool
+ConvertFilter::Set(const AudioFormat &_out_audio_format, Error &error)
+{
+	assert(in_audio_format.IsValid());
+	assert(_out_audio_format.IsValid());
+
+	if (_out_audio_format == out_audio_format)
+		/* no change */
+		return true;
+
+	if (out_audio_format.IsValid()) {
+		out_audio_format.Clear();
+		state->Close();
+	}
+
+	if (_out_audio_format == in_audio_format)
+		/* optimized special case: no-op */
+		return true;
+
+	if (!state->Open(in_audio_format, _out_audio_format, error))
+		return false;
+
+	out_audio_format = _out_audio_format;
+	return true;
+}
+
 AudioFormat
 ConvertFilter::Open(AudioFormat &audio_format, gcc_unused Error &error)
 {
 	assert(audio_format.IsValid());
 
-	in_audio_format = out_audio_format = audio_format;
+	in_audio_format = audio_format;
+	out_audio_format.Clear();
+
 	state.Construct();
 
 	return in_audio_format;
@@ -83,6 +107,11 @@ ConvertFilter::Open(AudioFormat &audio_format, gcc_unused Error &error)
 void
 ConvertFilter::Close()
 {
+	assert(in_audio_format.IsValid());
+
+	if (out_audio_format.IsValid())
+		state->Close();
+
 	state.Destruct();
 
 	poison_undefined(&in_audio_format, sizeof(in_audio_format));
@@ -93,15 +122,15 @@ const void *
 ConvertFilter::FilterPCM(const void *src, size_t src_size,
 			 size_t *dest_size_r, Error &error)
 {
-	if (in_audio_format == out_audio_format) {
+	assert(in_audio_format.IsValid());
+
+	if (!out_audio_format.IsValid()) {
 		/* optimized special case: no-op */
 		*dest_size_r = src_size;
 		return src;
 	}
 
-	return state->Convert(in_audio_format,
-			      src, src_size,
-			      out_audio_format, dest_size_r,
+	return state->Convert(src, src_size, dest_size_r,
 			      error);
 }
 
@@ -110,10 +139,11 @@ const struct filter_plugin convert_filter_plugin = {
 	convert_filter_init,
 };
 
-void
-convert_filter_set(Filter *_filter, const AudioFormat out_audio_format)
+bool
+convert_filter_set(Filter *_filter, AudioFormat out_audio_format,
+		   Error &error)
 {
 	ConvertFilter *filter = (ConvertFilter *)_filter;
 
-	filter->Set(out_audio_format);
+	return filter->Set(out_audio_format, error);
 }
diff --git a/src/filter/ConvertFilterPlugin.hxx b/src/filter/plugins/ConvertFilterPlugin.hxx
index c814aaf49..bb4673651 100644
--- a/src/filter/ConvertFilterPlugin.hxx
+++ b/src/filter/plugins/ConvertFilterPlugin.hxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -21,6 +21,7 @@
 #define MPD_CONVERT_FILTER_PLUGIN_HXX
 
 class Filter;
+class Error;
 struct AudioFormat;
 
 /**
@@ -29,7 +30,8 @@ struct AudioFormat;
  * format switch is a violation of the filter API, this filter must be
  * the last in a chain.
  */
-void
-convert_filter_set(Filter *filter, AudioFormat out_audio_format);
+bool
+convert_filter_set(Filter *filter, AudioFormat out_audio_format,
+		   Error &error);
 
 #endif
diff --git a/src/filter/NormalizeFilterPlugin.cxx b/src/filter/plugins/NormalizeFilterPlugin.cxx
index 6c4f6b0e5..58eb0c6a2 100644
--- a/src/filter/NormalizeFilterPlugin.cxx
+++ b/src/filter/plugins/NormalizeFilterPlugin.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -18,14 +18,13 @@
  */
 
 #include "config.h"
-#include "FilterPlugin.hxx"
-#include "FilterInternal.hxx"
-#include "FilterRegistry.hxx"
+#include "filter/FilterPlugin.hxx"
+#include "filter/FilterInternal.hxx"
+#include "filter/FilterRegistry.hxx"
 #include "pcm/PcmBuffer.hxx"
 #include "AudioFormat.hxx"
 #include "AudioCompress/compress.h"
 
-#include <assert.h>
 #include <string.h>
 
 class NormalizeFilter final : public Filter {
diff --git a/src/filter/NullFilterPlugin.cxx b/src/filter/plugins/NullFilterPlugin.cxx
index c762592f6..f79aa19f7 100644
--- a/src/filter/NullFilterPlugin.cxx
+++ b/src/filter/plugins/NullFilterPlugin.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -25,9 +25,9 @@
  */
 
 #include "config.h"
-#include "FilterPlugin.hxx"
-#include "FilterInternal.hxx"
-#include "FilterRegistry.hxx"
+#include "filter/FilterPlugin.hxx"
+#include "filter/FilterInternal.hxx"
+#include "filter/FilterRegistry.hxx"
 #include "AudioFormat.hxx"
 #include "Compiler.h"
 
diff --git a/src/filter/ReplayGainFilterPlugin.cxx b/src/filter/plugins/ReplayGainFilterPlugin.cxx
index b2dcde4cc..a5d9668cc 100644
--- a/src/filter/ReplayGainFilterPlugin.cxx
+++ b/src/filter/plugins/ReplayGainFilterPlugin.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -19,15 +19,16 @@
 
 #include "config.h"
 #include "ReplayGainFilterPlugin.hxx"
-#include "FilterPlugin.hxx"
-#include "FilterInternal.hxx"
-#include "FilterRegistry.hxx"
+#include "filter/FilterPlugin.hxx"
+#include "filter/FilterInternal.hxx"
+#include "filter/FilterRegistry.hxx"
 #include "AudioFormat.hxx"
 #include "ReplayGainInfo.hxx"
 #include "ReplayGainConfig.hxx"
-#include "MixerControl.hxx"
-#include "pcm/PcmVolume.hxx"
+#include "mixer/MixerControl.hxx"
+#include "pcm/Volume.hxx"
 #include "pcm/PcmBuffer.hxx"
+#include "util/ConstBuffer.hxx"
 #include "util/Error.hxx"
 #include "util/Domain.hxx"
 #include "Log.hxx"
@@ -55,8 +56,8 @@ class ReplayGainFilter final : public Filter {
 	ReplayGainInfo info;
 
 	/**
-	 * The current volume, between 0 and a value that may or may not exceed
-	 * #PCM_VOLUME_1.
+	 * About the current volume: it is between 0 and a value that
+	 * may or may not exceed #PCM_VOLUME_1.
 	 *
 	 * If the default value of true is used for replaygain_limit, the
 	 * application of the volume to the signal will never cause clipping.
@@ -66,16 +67,11 @@ class ReplayGainFilter final : public Filter {
 	 * maintain a consistent audio level. Whether clipping will actually
 	 * occur depends on what value the user is using for replaygain_preamp.
 	 */
-	unsigned volume;
-
-	AudioFormat format;
-
-	PcmBuffer buffer;
+	PcmVolume pv;
 
 public:
 	ReplayGainFilter()
-		:mixer(nullptr), mode(REPLAY_GAIN_OFF),
-		volume(PCM_VOLUME_1) {
+		:mixer(nullptr), mode(REPLAY_GAIN_OFF) {
 		info.Clear();
 	}
 
@@ -125,6 +121,7 @@ public:
 void
 ReplayGainFilter::Update()
 {
+	unsigned volume = PCM_VOLUME_1;
 	if (mode != REPLAY_GAIN_OFF) {
 		const auto &tuple = info.tuples[mode];
 		float scale = tuple.CalculateScale(replay_gain_preamp,
@@ -134,8 +131,9 @@ ReplayGainFilter::Update()
 			    "scale=%f\n", (double)scale);
 
 		volume = pcm_float_to_volume(scale);
-	} else
-		volume = PCM_VOLUME_1;
+	}
+
+	pv.SetVolume(volume);
 
 	if (mixer != nullptr) {
 		/* update the hardware mixer volume */
@@ -160,48 +158,25 @@ replay_gain_filter_init(gcc_unused const config_param &param,
 AudioFormat
 ReplayGainFilter::Open(AudioFormat &af, gcc_unused Error &error)
 {
-	format = af;
+	if (!pv.Open(af.format, error))
+		return AudioFormat::Undefined();
 
-	return format;
+	return af;
 }
 
 void
 ReplayGainFilter::Close()
 {
-	buffer.Clear();
+	pv.Close();
 }
 
 const void *
 ReplayGainFilter::FilterPCM(const void *src, size_t src_size,
-			    size_t *dest_size_r, Error &error)
+			    size_t *dest_size_r, gcc_unused Error &error)
 {
-
-	*dest_size_r = src_size;
-
-	if (volume == PCM_VOLUME_1)
-		/* optimized special case: 100% volume = no-op */
-		return src;
-
-	void *dest = buffer.Get(src_size);
-	if (volume <= 0) {
-		/* optimized special case: 0% volume = memset(0) */
-		/* XXX is this valid for all sample formats? What
-		   about floating point? */
-		memset(dest, 0, src_size);
-		return dest;
-	}
-
-	memcpy(dest, src, src_size);
-
-	bool success = pcm_volume(dest, src_size,
-				  format.format,
-				  volume);
-	if (!success) {
-		error.Set(replay_gain_domain, "pcm_volume() has failed");
-		return nullptr;
-	}
-
-	return dest;
+	const auto dest = pv.Apply({src, src_size});
+	*dest_size_r = dest.size;
+	return dest.data;
 }
 
 const struct filter_plugin replay_gain_filter_plugin = {
diff --git a/src/filter/ReplayGainFilterPlugin.hxx b/src/filter/plugins/ReplayGainFilterPlugin.hxx
index fbd1f2712..346541b97 100644
--- a/src/filter/ReplayGainFilterPlugin.hxx
+++ b/src/filter/plugins/ReplayGainFilterPlugin.hxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
diff --git a/src/filter/RouteFilterPlugin.cxx b/src/filter/plugins/RouteFilterPlugin.cxx
index d9042c21f..38c4ec43b 100644
--- a/src/filter/RouteFilterPlugin.cxx
+++ b/src/filter/plugins/RouteFilterPlugin.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -40,13 +40,12 @@
  */
 
 #include "config.h"
-#include "ConfigError.hxx"
-#include "ConfigData.hxx"
+#include "config/ConfigError.hxx"
+#include "config/ConfigData.hxx"
 #include "AudioFormat.hxx"
-#include "CheckAudioFormat.hxx"
-#include "FilterPlugin.hxx"
-#include "FilterInternal.hxx"
-#include "FilterRegistry.hxx"
+#include "filter/FilterPlugin.hxx"
+#include "filter/FilterInternal.hxx"
+#include "filter/FilterRegistry.hxx"
 #include "pcm/PcmBuffer.hxx"
 #include "util/StringUtil.hxx"
 #include "util/Error.hxx"
diff --git a/src/filter/VolumeFilterPlugin.cxx b/src/filter/plugins/VolumeFilterPlugin.cxx
index 1b663f6eb..c9b7aa89e 100644
--- a/src/filter/VolumeFilterPlugin.cxx
+++ b/src/filter/plugins/VolumeFilterPlugin.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -19,12 +19,12 @@
 
 #include "config.h"
 #include "VolumeFilterPlugin.hxx"
-#include "FilterPlugin.hxx"
-#include "FilterInternal.hxx"
-#include "FilterRegistry.hxx"
-#include "pcm/PcmVolume.hxx"
-#include "pcm/PcmBuffer.hxx"
+#include "filter/FilterPlugin.hxx"
+#include "filter/FilterInternal.hxx"
+#include "filter/FilterRegistry.hxx"
+#include "pcm/Volume.hxx"
 #include "AudioFormat.hxx"
+#include "util/ConstBuffer.hxx"
 #include "util/Error.hxx"
 #include "util/Domain.hxx"
 
@@ -32,29 +32,15 @@
 #include <string.h>
 
 class VolumeFilter final : public Filter {
-	/**
-	 * The current volume, from 0 to #PCM_VOLUME_1.
-	 */
-	unsigned volume;
-
-	AudioFormat format;
-
-	PcmBuffer buffer;
+	PcmVolume pv;
 
 public:
-	VolumeFilter()
-		:volume(PCM_VOLUME_1) {}
-
 	unsigned GetVolume() const {
-		assert(volume <= PCM_VOLUME_1);
-
-		return volume;
+		return pv.GetVolume();
 	}
 
 	void SetVolume(unsigned _volume) {
-		assert(_volume <= PCM_VOLUME_1);
-
-		volume = _volume;
+		pv.SetVolume(_volume);
 	}
 
 	virtual AudioFormat Open(AudioFormat &af, Error &error) override;
@@ -73,50 +59,27 @@ volume_filter_init(gcc_unused const config_param &param,
 }
 
 AudioFormat
-VolumeFilter::Open(AudioFormat &audio_format, gcc_unused Error &error)
+VolumeFilter::Open(AudioFormat &audio_format, Error &error)
 {
-	format = audio_format;
+	if (!pv.Open(audio_format.format, error))
+		return AudioFormat::Undefined();
 
-	return format;
+	return audio_format;
 }
 
 void
 VolumeFilter::Close()
 {
-	buffer.Clear();
+	pv.Close();
 }
 
 const void *
 VolumeFilter::FilterPCM(const void *src, size_t src_size,
-			size_t *dest_size_r, Error &error)
+			size_t *dest_size_r, gcc_unused Error &error)
 {
-	*dest_size_r = src_size;
-
-	if (volume >= PCM_VOLUME_1)
-		/* optimized special case: 100% volume = no-op */
-		return src;
-
-	void *dest = buffer.Get(src_size);
-
-	if (volume <= 0) {
-		/* optimized special case: 0% volume = memset(0) */
-		/* XXX is this valid for all sample formats? What
-		   about floating point? */
-		memset(dest, 0, src_size);
-		return dest;
-	}
-
-	memcpy(dest, src, src_size);
-
-	bool success = pcm_volume(dest, src_size,
-				  format.format,
-				  volume);
-	if (!success) {
-		error.Set(volume_domain, "pcm_volume() has failed");
-		return NULL;
-	}
-
-	return dest;
+	const auto dest = pv.Apply({src, src_size});
+	*dest_size_r = dest.size;
+	return dest.data;
 }
 
 const struct filter_plugin volume_filter_plugin = {
diff --git a/src/filter/VolumeFilterPlugin.hxx b/src/filter/plugins/VolumeFilterPlugin.hxx
index 822b7e93a..b5317dc6f 100644
--- a/src/filter/VolumeFilterPlugin.hxx
+++ b/src/filter/plugins/VolumeFilterPlugin.hxx
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify