Merge branch 'v0.22.x' into master

26 files changed, 326 insertions, 169 deletions

diff --git a/NEWS b/NEWS
index 2d9448207..3f3023a00 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,14 @@ ver 0.23 (not yet released)
 * protocol
   - new command "getvol"
 
+ver 0.22.3 (not yet released)
+* playlist
+  - add option "as_directory", making CUE file expansion optional
+* filter
+  - fix garbage after "Audio format not supported by filter" message
+  - ffmpeg: support planar output
+  - ffmpeg: support sample formats other than 16 bit
+
 ver 0.22.2 (2020/10/28)
 * database
   - simple: purge songs and virtual directories for unavailable plugins
diff --git a/doc/conf.py b/doc/conf.py
index fb9443dd3..2df29d071 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -38,7 +38,7 @@ author = 'Max Kellermann'
 # built documents.
 #
 # The short X.Y version.
-version = '0.22.2'
+version = '0.22.3'
 # The full version, including alpha/beta/rc tags.
 release = version
 
diff --git a/doc/plugins.rst b/doc/plugins.rst
index 107140942..06fe714c1 100644
--- a/doc/plugins.rst
+++ b/doc/plugins.rst
@@ -1229,23 +1229,25 @@ Playlist plugins
 asx
 ---
 
-Reads .asx playlist files.
+Reads :file:`.asx` playlist files.
+
+.. _cue_playlist:
 
 cue
 ---
-Reads .cue files.
+Reads :file:`.cue` files.
 
 embcue
 ------
-Reads CUE sheets from the "CUESHEET" tag of song files.
+Reads CUE sheets from the ``CUESHEET`` tag of song files.
 
 m3u
 ---
-Reads .m3u playlist files.
+Reads :file:`.m3u` playlist files.
 
 extm3u
 ------
-Reads extended .m3u playlist files.
+Reads extended :file:`.m3u` playlist files.
 
 flac
 ----
@@ -1253,11 +1255,11 @@ Reads the cuesheet metablock from a FLAC file.
 
 pls
 ---
-Reads .pls playlist files.
+Reads :file:`.pls` playlist files.
 
 rss
 ---
-Reads music links from .rss files.
+Reads music links from :file:`.rss` files.
 
 soundcloud
 ----------
diff --git a/doc/user.rst b/doc/user.rst
index db87ee7d0..abd7c7b1f 100644
--- a/doc/user.rst
+++ b/doc/user.rst
@@ -413,7 +413,7 @@ The following table lists the audio_output options valid for all plugins:
    * - **format samplerate:bits:channels**
      -  Always open the audio output with the specified audio format, regardless of the format of the input file. This is optional for most plugins.
         See :ref:`audio_output_format` for a detailed description of the value.
-   * - **enabed yes|no**
+   * - **enabled yes|no**
      - Specifies whether this audio output is enabled when :program:`MPD` is started. By default, all audio outputs are enabled. This is just the default setting when there is no state file; with a state file, the previous state is restored.
    * - **tags yes|no**
      - If set to no, then :program:`MPD` will not send tags to this output. This is only useful for output plugins that can receive tags, for example the httpd output plugin.
@@ -500,6 +500,11 @@ The following table lists the playlist_plugin options valid for all plugins:
      - The name of the plugin
    * - **enabled yes|no**
      - Allows you to disable a playlist plugin without recompiling. By default, all plugins are enabled.
+   * - **as_directory yes|no**
+     - With this option, a playlist file of this type is parsed during
+       database update and converted to a virtual directory, allowing
+       MPD clients to access individual entries.  By default, this is
+       only enabled for the :ref:`cue plugin <cue_playlist>`.
 
 More information can be found in the :ref:`playlist_plugins`
 reference.
diff --git a/meson.build b/meson.build
index c1cf5b569..dce9ca2ea 100644
--- a/meson.build
+++ b/meson.build
@@ -4,8 +4,8 @@ project(
   version: '0.23~git',
   meson_version: '>= 0.49.0',
   default_options: [
-    'c_std=c99',
-    'build.c_std=c99',
+    'c_std=c11',
+    'build.c_std=c11',
     'cpp_std=c++17',
     'build.cpp_std=c++17',
     'warning_level=3',
@@ -96,6 +96,11 @@ test_cflags = test_common_flags + [
 ]
 
 test_ldflags = [
+  # make relocations read-only (hardening)
+  '-Wl,-z,relro',
+
+  # no lazy binding, please - not worth it for a daemon
+  '-Wl,-z,now',
 ]
 
 if get_option('buildtype') != 'debug'
diff --git a/src/db/update/Playlist.cxx b/src/db/update/Playlist.cxx
index 03509522a..46286bb90 100644
--- a/src/db/update/Playlist.cxx
+++ b/src/db/update/Playlist.cxx
@@ -95,7 +95,7 @@ UpdateWalk::UpdatePlaylistFile(Directory &directory,
 	if (plugin == nullptr)
 		return false;
 
-	if (plugin->as_folder)
+	if (GetPlaylistPluginAsFolder(*plugin))
 		UpdatePlaylistFile(directory, name, info, *plugin);
 
 	PlaylistInfo pi(name, info.mtime);
diff --git a/src/db/update/SpecialDirectory.cxx b/src/db/update/SpecialDirectory.cxx
index 49c025d18..368bfb2db 100644
--- a/src/db/update/SpecialDirectory.cxx
+++ b/src/db/update/SpecialDirectory.cxx
@@ -52,7 +52,16 @@ static bool
 HavePlaylistPluginForFilename(const char *filename) noexcept
 {
 	const char *suffix = PathTraitsUTF8::GetFilenameSuffix(filename);
-	return suffix != nullptr && playlist_suffix_supported(suffix);
+	if (suffix == nullptr)
+		return false;
+
+	const auto plugin = FindPlaylistPluginBySuffix(suffix);
+	if (plugin == nullptr)
+		return false;
+
+	/* discard the special directory if the user disables the
+	   plugin's "as_directory" setting */
+	return GetPlaylistPluginAsFolder(*plugin);
 }
 
 bool
diff --git a/src/decoder/plugins/FfmpegDecoderPlugin.cxx b/src/decoder/plugins/FfmpegDecoderPlugin.cxx
index 1a601a55d..05940fc41 100644
--- a/src/decoder/plugins/FfmpegDecoderPlugin.cxx
+++ b/src/decoder/plugins/FfmpegDecoderPlugin.cxx
@@ -25,6 +25,7 @@
 #include "lib/ffmpeg/Domain.hxx"
 #include "lib/ffmpeg/Error.hxx"
 #include "lib/ffmpeg/Init.hxx"
+#include "lib/ffmpeg/Interleave.hxx"
 #include "lib/ffmpeg/Buffer.hxx"
 #include "lib/ffmpeg/Frame.hxx"
 #include "lib/ffmpeg/Format.hxx"
@@ -177,48 +178,6 @@ start_time_fallback(const AVStream &stream)
 }
 
 /**
- * Copy PCM data from a non-empty AVFrame to an interleaved buffer.
- *
- * Throws #std::exception on error.
- */
-static ConstBuffer<void>
-copy_interleave_frame(const AVCodecContext &codec_context,
-		      const AVFrame &frame,
-		      FfmpegBuffer &global_buffer)
-{
-	assert(frame.nb_samples > 0);
-
-	int plane_size;
-	const int data_size =
-		av_samples_get_buffer_size(&plane_size,
-					   codec_context.channels,
-					   frame.nb_samples,
-					   codec_context.sample_fmt, 1);
-	assert(data_size != 0);
-	if (data_size < 0)
-		throw MakeFfmpegError(data_size);
-
-	void *output_buffer;
-	if (av_sample_fmt_is_planar(codec_context.sample_fmt) &&
-	    codec_context.channels > 1) {
-		output_buffer = global_buffer.GetT<uint8_t>(data_size);
-		if (output_buffer == nullptr)
-			/* Not enough memory - shouldn't happen */
-			throw std::bad_alloc();
-
-		PcmInterleave(output_buffer,
-			      ConstBuffer<const void *>((const void *const*)frame.extended_data,
-							codec_context.channels),
-			      frame.nb_samples,
-			      av_get_bytes_per_sample(codec_context.sample_fmt));
-	} else {
-		output_buffer = frame.extended_data[0];
-	}
-
-	return { output_buffer, (size_t)data_size };
-}
-
-/**
  * Convert AVPacket::pts to a stream-relative time stamp (still in
  * AVStream::time_base units).  Returns a negative value on error.
  */
@@ -258,7 +217,7 @@ FfmpegSendFrame(DecoderClient &client, InputStream *is,
 		FfmpegBuffer &buffer)
 {
 	ConstBuffer<void> output_buffer =
-		copy_interleave_frame(codec_context, frame, buffer);
+		Ffmpeg::InterleaveFrame(frame, buffer);
 
 	if (skip_bytes > 0) {
 		if (skip_bytes >= output_buffer.size) {
diff --git a/src/filter/LoadChain.cxx b/src/filter/LoadChain.cxx
index 26e6f883a..cca351a72 100644
--- a/src/filter/LoadChain.cxx
+++ b/src/filter/LoadChain.cxx
@@ -20,19 +20,24 @@
 #include "LoadChain.hxx"
 #include "Factory.hxx"
 #include "Prepared.hxx"
+#include "plugins/AutoConvertFilterPlugin.hxx"
 #include "plugins/ChainFilterPlugin.hxx"
+#include "util/IterableSplitString.hxx"
 
-#include <algorithm>
 #include <string>
 
-#include <string.h>
-
 static void
 filter_chain_append_new(PreparedFilter &chain, FilterFactory &factory,
-			const char *template_name)
+			std::string_view template_name)
 {
+	/* using the AutoConvert filter just in case the specified
+	   filter plugin does not support the exact input format */
+
 	filter_chain_append(chain, template_name,
-			    factory.MakeFilter(template_name));
+			    /* unfortunately, MakeFilter() wants a
+			       null-terminated string, so we need to
+			       copy it here */
+			    autoconvert_filter_new(factory.MakeFilter(std::string(template_name).c_str())));
 }
 
 void
@@ -40,18 +45,10 @@ filter_chain_parse(PreparedFilter &chain,
 		   FilterFactory &factory,
 		   const char *spec)
 {
-	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);
-			filter_chain_append_new(chain, factory, name.c_str());
-		}
-
-		if (comma == end)
-			break;
+	for (const std::string_view i : IterableSplitString(spec, ',')) {
+		if (i.empty())
+			continue;
 
-		spec = comma + 1;
+		filter_chain_append_new(chain, factory, i);
 	}
 }
diff --git a/src/filter/plugins/AutoConvertFilterPlugin.cxx b/src/filter/plugins/AutoConvertFilterPlugin.cxx
index 54c692406..b9bbd256f 100644
--- a/src/filter/plugins/AutoConvertFilterPlugin.cxx
+++ b/src/filter/plugins/AutoConvertFilterPlugin.cxx
@@ -19,6 +19,7 @@
 
 #include "AutoConvertFilterPlugin.hxx"
 #include "ConvertFilterPlugin.hxx"
+#include "TwoFilters.hxx"
 #include "filter/Filter.hxx"
 #include "filter/Prepared.hxx"
 #include "pcm/AudioFormat.hxx"
@@ -27,35 +28,6 @@
 #include <cassert>
 #include <memory>
 
-class AutoConvertFilter final : public Filter {
-	/**
-	 * The underlying filter.
-	 */
-	std::unique_ptr<Filter> filter;
-
-	/**
-	 * A convert_filter, just in case conversion is needed.  nullptr
-	 * if unused.
-	 */
-	std::unique_ptr<Filter> convert;
-
-public:
-	AutoConvertFilter(std::unique_ptr<Filter> &&_filter,
-			  std::unique_ptr<Filter> &&_convert)
-		:Filter(_filter->GetOutAudioFormat()),
-		 filter(std::move(_filter)), convert(std::move(_convert)) {}
-
-	void Reset() noexcept override {
-		filter->Reset();
-
-		if (convert)
-			convert->Reset();
-	}
-
-	ConstBuffer<void> FilterPCM(ConstBuffer<void> src) override;
-	ConstBuffer<void> Flush() override;
-};
-
 class PreparedAutoConvertFilter final : public PreparedFilter {
 	/**
 	 * The underlying filter.
@@ -81,37 +53,17 @@ PreparedAutoConvertFilter::Open(AudioFormat &in_audio_format)
 
 	/* need to convert? */
 
-	std::unique_ptr<Filter> convert;
-	if (in_audio_format != child_audio_format) {
-		/* yes - create a convert_filter */
-
-		convert.reset(convert_filter_new(in_audio_format,
-						 child_audio_format));
-	}
-
-	return std::make_unique<AutoConvertFilter>(std::move(new_filter),
-						   std::move(convert));
-}
+	if (in_audio_format == child_audio_format)
+		/* no */
+		return new_filter;
 
-ConstBuffer<void>
-AutoConvertFilter::FilterPCM(ConstBuffer<void> src)
-{
-	if (convert != nullptr)
-		src = convert->FilterPCM(src);
+	/* yes - create a convert_filter */
 
-	return filter->FilterPCM(src);
-}
-
-ConstBuffer<void>
-AutoConvertFilter::Flush()
-{
-	if (convert != nullptr) {
-		auto result = convert->Flush();
-		if (!result.IsNull())
-			return filter->FilterPCM(result);
-	}
+	auto convert = convert_filter_new(in_audio_format,
+					  child_audio_format);
 
-	return filter->Flush();
+	return std::make_unique<TwoFilters>(std::move(convert),
+					    std::move(new_filter));
 }
 
 std::unique_ptr<PreparedFilter>
diff --git a/src/filter/plugins/ChainFilterPlugin.cxx b/src/filter/plugins/ChainFilterPlugin.cxx
index 07bca48af..249130081 100644
--- a/src/filter/plugins/ChainFilterPlugin.cxx
+++ b/src/filter/plugins/ChainFilterPlugin.cxx
@@ -28,15 +28,14 @@
 #include <cassert>
 #include <list>
 #include <memory>
+#include <string>
 
 class ChainFilter final : public Filter {
 	struct Child {
-		const char *name;
 		std::unique_ptr<Filter> filter;
 
-		Child(const char *_name,
-		      std::unique_ptr<Filter> _filter) noexcept
-			:name(_name), filter(std::move(_filter)) {}
+		explicit Child(std::unique_ptr<Filter> &&_filter) noexcept
+			:filter(std::move(_filter)) {}
 	};
 
 	std::list<Child> children;
@@ -50,13 +49,12 @@ public:
 	explicit ChainFilter(AudioFormat _audio_format)
 		:Filter(_audio_format) {}
 
-	void Append(const char *name,
-		    std::unique_ptr<Filter> filter) noexcept {
+	void Append(std::unique_ptr<Filter> filter) noexcept {
 		assert(out_audio_format.IsValid());
 		out_audio_format = filter->GetOutAudioFormat();
 		assert(out_audio_format.IsValid());
 
-		children.emplace_back(name, std::move(filter));
+		children.emplace_back(std::move(filter));
 
 		RewindFlush();
 	}
@@ -75,10 +73,10 @@ private:
 
 class PreparedChainFilter final : public PreparedFilter {
 	struct Child {
-		const char *name;
+		const std::string name;
 		std::unique_ptr<PreparedFilter> filter;
 
-		Child(const char *_name,
+		Child(std::string_view _name,
 		      std::unique_ptr<PreparedFilter> _filter)
 			:name(_name), filter(std::move(_filter)) {}
 
@@ -91,7 +89,7 @@ class PreparedChainFilter final : public PreparedFilter {
 	std::list<Child> children;
 
 public:
-	void Append(const char *name,
+	void Append(std::string_view name,
 		    std::unique_ptr<PreparedFilter> filter) noexcept {
 		children.emplace_back(name, std::move(filter));
 	}
@@ -108,7 +106,7 @@ PreparedChainFilter::Child::Open(const AudioFormat &prev_audio_format)
 
 	if (conv_audio_format != prev_audio_format)
 		throw FormatRuntimeError("Audio format not supported by filter '%s': %s",
-					 name,
+					 name.c_str(),
 					 ToString(prev_audio_format).c_str());
 
 	return new_filter;
@@ -121,7 +119,7 @@ PreparedChainFilter::Open(AudioFormat &in_audio_format)
 
 	for (auto &child : children) {
 		AudioFormat audio_format = chain->GetOutAudioFormat();
-		chain->Append(child.name, child.Open(audio_format));
+		chain->Append(child.Open(audio_format));
 	}
 
 	return chain;
@@ -177,7 +175,7 @@ filter_chain_new() noexcept
 }
 
 void
-filter_chain_append(PreparedFilter &_chain, const char *name,
+filter_chain_append(PreparedFilter &_chain, std::string_view name,
 		    std::unique_ptr<PreparedFilter> filter) noexcept
 {
 	auto &chain = (PreparedChainFilter &)_chain;
diff --git a/src/filter/plugins/ChainFilterPlugin.hxx b/src/filter/plugins/ChainFilterPlugin.hxx
index 06eb7c60a..8dd7e526c 100644
--- a/src/filter/plugins/ChainFilterPlugin.hxx
+++ b/src/filter/plugins/ChainFilterPlugin.hxx
@@ -28,6 +28,7 @@
 #define MPD_FILTER_CHAIN_HXX
 
 #include <memory>
+#include <string_view>
 
 class PreparedFilter;
 
@@ -45,7 +46,7 @@ filter_chain_new() noexcept;
  * @param filter the filter to be appended to #chain
  */
 void
-filter_chain_append(PreparedFilter &chain, const char *name,
+filter_chain_append(PreparedFilter &chain, std::string_view name,
 		    std::unique_ptr<PreparedFilter> filter) noexcept;
 
 #endif
diff --git a/src/filter/plugins/ConvertFilterPlugin.cxx b/src/filter/plugins/ConvertFilterPlugin.cxx
index 91ddddeef..d04d09da6 100644
--- a/src/filter/plugins/ConvertFilterPlugin.cxx
+++ b/src/filter/plugins/ConvertFilterPlugin.cxx
@@ -117,13 +117,13 @@ convert_filter_prepare() noexcept
 	return std::make_unique<PreparedConvertFilter>();
 }
 
-Filter *
+std::unique_ptr<Filter>
 convert_filter_new(const AudioFormat in_audio_format,
 		   const AudioFormat out_audio_format)
 {
 	std::unique_ptr<ConvertFilter> filter(new ConvertFilter(in_audio_format));
 	filter->Set(out_audio_format);
-	return filter.release();
+	return filter;
 }
 
 void
diff --git a/src/filter/plugins/ConvertFilterPlugin.hxx b/src/filter/plugins/ConvertFilterPlugin.hxx
index a5299147e..0f78da519 100644
--- a/src/filter/plugins/ConvertFilterPlugin.hxx
+++ b/src/filter/plugins/ConvertFilterPlugin.hxx
@@ -29,7 +29,7 @@ struct AudioFormat;
 std::unique_ptr<PreparedFilter>
 convert_filter_prepare() noexcept;
 
-Filter *
+std::unique_ptr<Filter>
 convert_filter_new(AudioFormat in_audio_format,
 		   AudioFormat out_audio_format);
 
diff --git a/src/filter/plugins/FfmpegFilter.cxx b/src/filter/plugins/FfmpegFilter.cxx
index 1b841833a..cd076200b 100644
--- a/src/filter/plugins/FfmpegFilter.cxx
+++ b/src/filter/plugins/FfmpegFilter.cxx
@@ -18,6 +18,7 @@
  */
 
 #include "FfmpegFilter.hxx"
+#include "lib/ffmpeg/Interleave.hxx"
 #include "lib/ffmpeg/SampleFormat.hxx"
 #include "util/ConstBuffer.hxx"
 
@@ -79,5 +80,5 @@ FfmpegFilter::FilterPCM(ConstBuffer<void> src)
 	/* TODO: call av_buffersink_get_frame() repeatedly?  Not
 	   possible with MPD's current Filter API */
 
-	return {frame.GetData(0), frame->nb_samples * GetOutAudioFormat().GetFrameSize()};
+	return Ffmpeg::InterleaveFrame(*frame, interleave_buffer);
 }
diff --git a/src/filter/plugins/FfmpegFilter.hxx b/src/filter/plugins/FfmpegFilter.hxx
index 8a048cffc..286780d9d 100644
--- a/src/filter/plugins/FfmpegFilter.hxx
+++ b/src/filter/plugins/FfmpegFilter.hxx
@@ -21,6 +21,7 @@
 #define MPD_FFMPEG_FILTER__HXX
 
 #include "filter/Filter.hxx"
+#include "lib/ffmpeg/Buffer.hxx"
 #include "lib/ffmpeg/Filter.hxx"
 #include "lib/ffmpeg/Frame.hxx"
 
@@ -32,6 +33,8 @@ class FfmpegFilter final : public Filter {
 	Ffmpeg::FilterContext buffer_src, buffer_sink;
 	Ffmpeg::Frame frame;
 
+	FfmpegBuffer interleave_buffer;
+
 	const int in_format, in_sample_rate, in_channels;
 
 	const size_t in_audio_frame_size;
diff --git a/src/filter/plugins/TwoFilters.cxx b/src/filter/plugins/TwoFilters.cxx
new file mode 100644
index 000000000..0defa5799
--- /dev/null
+++ b/src/filter/plugins/TwoFilters.cxx
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2003-2020 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 "TwoFilters.hxx"
+#include "util/ConstBuffer.hxx"
+
+ConstBuffer<void>
+TwoFilters::FilterPCM(ConstBuffer<void> src)
+{
+	return second->FilterPCM(first->FilterPCM(src));
+}
+
+ConstBuffer<void>
+TwoFilters::Flush()
+{
+	auto result = first->Flush();
+	if (!result.IsNull())
+		/* Flush() output from the first Filter must be
+		   filtered by the second Filter */
+		return second->FilterPCM(result);
+
+	return second->Flush();
+}
diff --git a/src/filter/plugins/TwoFilters.hxx b/src/filter/plugins/TwoFilters.hxx
new file mode 100644
index 000000000..cbd86a6df
--- /dev/null
+++ b/src/filter/plugins/TwoFilters.hxx
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2003-2020 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.
+ */
+
+#ifndef MPD_WITH_CONVERT_FILTER_HXX
+#define MPD_WITH_CONVERT_FILTER_HXX
+
+#include "filter/Filter.hxx"
+
+#include <memory>
+
+/**
+ * A #Filter implementation which chains two other filters.
+ */
+class TwoFilters final : public Filter {
+	std::unique_ptr<Filter> first, second;
+
+public:
+	template<typename F, typename S>
+	TwoFilters(F &&_first, S &&_second) noexcept
+		:Filter(_second->GetOutAudioFormat()),
+		 first(std::forward<F>(_first)),
+		 second(std::forward<S>(_second)) {}
+
+	void Reset() noexcept override {
+		first->Reset();
+		second->Reset();
+	}
+
+	ConstBuffer<void> FilterPCM(ConstBuffer<void> src) override;
+	ConstBuffer<void> Flush() override;
+};
+
+#endif
diff --git a/src/filter/plugins/meson.build b/src/filter/plugins/meson.build
index 8ad526c3d..cf313f20b 100644
--- a/src/filter/plugins/meson.build
+++ b/src/filter/plugins/meson.build
@@ -14,6 +14,7 @@ filter_plugins = static_library(
   'filter_plugins',
   '../../AudioCompress/compress.c',
   'NullFilterPlugin.cxx',
+  'TwoFilters.cxx',
   'ChainFilterPlugin.cxx',
   'AutoConvertFilterPlugin.cxx',
   'ConvertFilterPlugin.cxx',
diff --git a/src/lib/ffmpeg/Buffer.hxx b/src/lib/ffmpeg/Buffer.hxx
index cab4375d9..300c5bf19 100644
--- a/src/lib/ffmpeg/Buffer.hxx
+++ b/src/lib/ffmpeg/Buffer.hxx
@@ -20,36 +20,36 @@
 #ifndef MPD_FFMPEG_BUFFER_HXX
 #define MPD_FFMPEG_BUFFER_HXX
 
+#include "util/Compiler.h"
+
 extern "C" {
 #include <libavutil/mem.h>
 }
 
 #include <cstddef>
 
-/* suppress the ffmpeg compatibility macro */
-#ifdef SampleFormat
-#undef SampleFormat
-#endif
-
 class FfmpegBuffer {
-	void *data;
-	unsigned size;
+	void *data = nullptr;
+	unsigned size = 0;
 
 public:
-	FfmpegBuffer():data(nullptr), size(0) {}
+	FfmpegBuffer() noexcept = default;
 
-	~FfmpegBuffer() {
+	~FfmpegBuffer() noexcept {
 		av_free(data);
 	}
 
+	FfmpegBuffer(const FfmpegBuffer &) = delete;
+	FfmpegBuffer &operator=(const FfmpegBuffer &) = delete;
+
 	gcc_malloc
-	void *Get(size_t min_size) {
+	void *Get(size_t min_size) noexcept {
 		av_fast_malloc(&data, &size, min_size);
 		return data;
 	}
 
 	template<typename T>
-	T *GetT(size_t n) {
+	T *GetT(size_t n) noexcept {
 		return (T *)Get(n * sizeof(T));
 	}
 };
diff --git a/src/lib/ffmpeg/Interleave.cxx b/src/lib/ffmpeg/Interleave.cxx
new file mode 100644
index 000000000..93a9a8bef
--- /dev/null
+++ b/src/lib/ffmpeg/Interleave.cxx
@@ -0,0 +1,71 @@
+/*
+ * Copyright 2003-2020 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 "Interleave.hxx"
+#include "Buffer.hxx"
+#include "Error.hxx"
+#include "pcm/Interleave.hxx"
+#include "util/ConstBuffer.hxx"
+
+extern "C" {
+#include <libavutil/frame.h>
+}
+
+#include <cassert>
+#include <new> // for std::bad_alloc
+
+namespace Ffmpeg {
+
+ConstBuffer<void>
+InterleaveFrame(const AVFrame &frame, FfmpegBuffer &buffer)
+{
+	assert(frame.nb_samples > 0);
+
+	const AVSampleFormat format = AVSampleFormat(frame.format);
+	const unsigned channels = frame.channels;
+	const std::size_t n_frames = frame.nb_samples;
+
+	int plane_size;
+	const int data_size =
+		av_samples_get_buffer_size(&plane_size, channels,
+					   n_frames, format, 1);
+	assert(data_size != 0);
+	if (data_size < 0)
+		throw MakeFfmpegError(data_size);
+
+	void *output_buffer;
+	if (av_sample_fmt_is_planar(format) && channels > 1) {
+		output_buffer = buffer.GetT<uint8_t>(data_size);
+		if (output_buffer == nullptr)
+			/* Not enough memory - shouldn't happen */
+			throw std::bad_alloc();
+
+		PcmInterleave(output_buffer,
+			      ConstBuffer<const void *>((const void *const*)frame.extended_data,
+							channels),
+			      n_frames,
+			      av_get_bytes_per_sample(format));
+	} else {
+		output_buffer = frame.extended_data[0];
+	}
+
+	return { output_buffer, (size_t)data_size };
+}
+
+} // namespace Ffmpeg
diff --git a/src/lib/ffmpeg/Interleave.hxx b/src/lib/ffmpeg/Interleave.hxx
new file mode 100644
index 000000000..f2d433620
--- /dev/null
+++ b/src/lib/ffmpeg/Interleave.hxx
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2003-2020 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.
+ */
+
+#ifndef MPD_FFMPEG_INTERLEAVE_HXX
+#define MPD_FFMPEG_INTERLEAVE_HXX
+
+struct AVFrame;
+template<typename T> struct ConstBuffer;
+class FfmpegBuffer;
+
+namespace Ffmpeg {
+
+/**
+ * Return interleaved data from the given non-empty #AVFrame.  If the
+ * data is planar, then the data is copied to a buffer.
+ *
+ * Throws on error.
+ */
+ConstBuffer<void>
+InterleaveFrame(const AVFrame &frame, FfmpegBuffer &buffer);
+
+} // namespace Ffmpeg
+
+#endif
diff --git a/src/lib/ffmpeg/Time.hxx b/src/lib/ffmpeg/Time.hxx
index 03b8e8bce..39ebd3855 100644
--- a/src/lib/ffmpeg/Time.hxx
+++ b/src/lib/ffmpeg/Time.hxx
@@ -31,11 +31,6 @@ extern "C" {
 #include <cassert>
 #include <cstdint>
 
-/* suppress the ffmpeg compatibility macro */
-#ifdef SampleFormat
-#undef SampleFormat
-#endif
-
 /* redefine AV_TIME_BASE_Q because libavutil's macro definition is a
    compound literal, which is illegal in C++ */
 #ifdef AV_TIME_BASE_Q
diff --git a/src/lib/ffmpeg/meson.build b/src/lib/ffmpeg/meson.build
index 0a0217ccf..fde110edc 100644
--- a/src/lib/ffmpeg/meson.build
+++ b/src/lib/ffmpeg/meson.build
@@ -26,6 +26,7 @@ endif
 ffmpeg = static_library(
   'ffmpeg',
   'Init.cxx',
+  'Interleave.cxx',
   'LogError.cxx',
   'LogCallback.cxx',
   'Error.cxx',
diff --git a/src/playlist/PlaylistRegistry.cxx b/src/playlist/PlaylistRegistry.cxx
index 9aa87b73b..b9f6bb7ec 100644
--- a/src/playlist/PlaylistRegistry.cxx
+++ b/src/playlist/PlaylistRegistry.cxx
@@ -71,6 +71,9 @@ static constexpr unsigned n_playlist_plugins =
 /** which plugins have been initialized successfully? */
 static bool playlist_plugins_enabled[n_playlist_plugins];
 
+/** which plugins have the "as_folder" option enabled? */
+static bool playlist_plugins_as_folder[n_playlist_plugins];
+
 #define playlist_plugins_for_each_enabled(plugin) \
 	playlist_plugins_for_each(plugin) \
 		if (playlist_plugins_enabled[playlist_plugin_iterator - playlist_plugins])
@@ -96,6 +99,10 @@ playlist_list_global_init(const ConfigData &config)
 
 		playlist_plugins_enabled[i] =
 			playlist_plugin_init(playlist_plugins[i], *param);
+
+		playlist_plugins_as_folder[i] =
+			param->GetBlockValue("as_directory",
+					     playlist_plugins[i]->as_folder);
 	}
 }
 
@@ -106,6 +113,16 @@ playlist_list_global_finish() noexcept
 		playlist_plugin_finish(plugin);
 }
 
+bool
+GetPlaylistPluginAsFolder(const PlaylistPlugin &plugin) noexcept
+{
+	/* this loop has no end condition because it must finish when
+	   the plugin was found */
+	for (std::size_t i = 0;; ++i)
+		if (playlist_plugins[i] == &plugin)
+			return playlist_plugins_as_folder[i];
+}
+
 static std::unique_ptr<SongEnumerator>
 playlist_list_open_uri_scheme(const char *uri, Mutex &mutex,
 			      bool *tried)
@@ -207,11 +224,7 @@ gcc_pure
 static StringView
 ExtractMimeTypeMainPart(StringView s) noexcept
 {
-	const auto separator = s.Find(';');
-	if (separator != nullptr)
-		s.SetEnd(separator);
-
-	return s;
+	return s.Split(';').first;
 }
 
 static std::unique_ptr<SongEnumerator>
diff --git a/src/playlist/PlaylistRegistry.hxx b/src/playlist/PlaylistRegistry.hxx
index 5e38ca23a..205fbb4b2 100644
--- a/src/playlist/PlaylistRegistry.hxx
+++ b/src/playlist/PlaylistRegistry.hxx
@@ -60,6 +60,14 @@ public:
 };
 
 /**
+ * Shall this playlists supported by this plugin be represented as
+ * directories in the database?
+ */
+gcc_const
+bool
+GetPlaylistPluginAsFolder(const PlaylistPlugin &plugin) noexcept;
+
+/**
  * Opens a playlist by its URI.
  */
 std::unique_ptr<SongEnumerator>