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diff --git a/src/decoder/DecoderControl.hxx b/src/decoder/DecoderControl.hxx
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+/*
+ * 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.
+ */
+
+#ifndef MPD_DECODER_CONTROL_HXX
+#define MPD_DECODER_CONTROL_HXX
+
+#include "DecoderCommand.hxx"
+#include "AudioFormat.hxx"
+#include "MixRampInfo.hxx"
+#include "thread/Mutex.hxx"
+#include "thread/Cond.hxx"
+#include "thread/Thread.hxx"
+#include "util/Error.hxx"
+
+#include <assert.h>
+#include <stdint.h>
+
+/* damn you, windows.h! */
+#ifdef ERROR
+#undef ERROR
+#endif
+
+class DetachedSong;
+class MusicBuffer;
+class MusicPipe;
+
+enum class DecoderState : uint8_t {
+	STOP = 0,
+	START,
+	DECODE,
+
+	/**
+	 * The last "START" command failed, because there was an I/O
+	 * error or because no decoder was able to decode the file.
+	 * This state will only come after START; once the state has
+	 * turned to DECODE, by definition no such error can occur.
+	 */
+	ERROR,
+};
+
+struct DecoderControl {
+	/**
+	 * The handle of the decoder thread.
+	 */
+	Thread thread;
+
+	/**
+	 * This lock protects #state and #command.
+	 *
+	 * This is usually a reference to PlayerControl::mutex, so
+	 * that both player thread and decoder thread share a mutex.
+	 * This simplifies synchronization with #cond and
+	 * #client_cond.
+	 */
+	Mutex &mutex;
+
+	/**
+	 * Trigger this object after you have modified #command.  This
+	 * is also used by the decoder thread to notify the caller
+	 * when it has finished a command.
+	 */
+	Cond cond;
+
+	/**
+	 * The trigger of this object's client.  It is signalled
+	 * whenever an event occurs.
+	 *
+	 * This is usually a reference to PlayerControl::cond.
+	 */
+	Cond &client_cond;
+
+	DecoderState state;
+	DecoderCommand command;
+
+	/**
+	 * The error that occurred in the decoder thread.  This
+	 * attribute is only valid if #state is #DecoderState::ERROR.
+	 * The object must be freed when this object transitions to
+	 * any other state (usually #DecoderState::START).
+	 */
+	Error error;
+
+	bool quit;
+
+	/**
+	 * Is the client currently waiting for the DecoderThread?  If
+	 * false, the DecoderThread may omit invoking Cond::signal(),
+	 * reducing the number of system calls.
+	 */
+	bool client_is_waiting;
+
+	bool seek_error;
+	bool seekable;
+	double seek_where;
+
+	/** the format of the song file */
+	AudioFormat in_audio_format;
+
+	/** the format being sent to the music pipe */
+	AudioFormat out_audio_format;
+
+	/**
+	 * The song currently being decoded.  This attribute is set by
+	 * the player thread, when it sends the #DecoderCommand::START
+	 * command.
+	 *
+	 * This is a duplicate, and must be freed when this attribute
+	 * is cleared.
+	 */
+	DetachedSong *song;
+
+	/**
+	 * The initial seek position (in milliseconds), e.g. to the
+	 * start of a sub-track described by a CUE file.
+	 *
+	 * This attribute is set by dc_start().
+	 */
+	unsigned start_ms;
+
+	/**
+	 * The decoder will stop when it reaches this position (in
+	 * milliseconds).  0 means don't stop before the end of the
+	 * file.
+	 *
+	 * This attribute is set by dc_start().
+	 */
+	unsigned end_ms;
+
+	float total_time;
+
+	/** the #music_chunk allocator */
+	MusicBuffer *buffer;
+
+	/**
+	 * The destination pipe for decoded chunks.  The caller thread
+	 * owns this object, and is responsible for freeing it.
+	 */
+	MusicPipe *pipe;
+
+	float replay_gain_db;
+	float replay_gain_prev_db;
+
+	MixRampInfo mix_ramp, previous_mix_ramp;
+
+	/**
+	 * @param _mutex see #mutex
+	 * @param _client_cond see #client_cond
+	 */
+	DecoderControl(Mutex &_mutex, Cond &_client_cond);
+	~DecoderControl();
+
+	/**
+	 * Locks the object.
+	 */
+	void Lock() const {
+		mutex.lock();
+	}
+
+	/**
+	 * Unlocks the object.
+	 */
+	void Unlock() const {
+		mutex.unlock();
+	}
+
+	/**
+	 * Signals the object.  This function is only valid in the
+	 * player thread.  The object should be locked prior to
+	 * calling this function.
+	 */
+	void Signal() {
+		cond.signal();
+	}
+
+	/**
+	 * Waits for a signal on the #DecoderControl object.  This function
+	 * is only valid in the decoder thread.  The object must be locked
+	 * prior to calling this function.
+	 */
+	void Wait() {
+		cond.wait(mutex);
+	}
+
+	/**
+	 * Waits for a signal from the decoder thread.  This object
+	 * must be locked prior to calling this function.  This method
+	 * is only valid in the player thread.
+	 *
+	 * Caller must hold the lock.
+	 */
+	void WaitForDecoder();
+
+	bool IsIdle() const {
+		return state == DecoderState::STOP ||
+			state == DecoderState::ERROR;
+	}
+
+	gcc_pure
+	bool LockIsIdle() const {
+		Lock();
+		bool result = IsIdle();
+		Unlock();
+		return result;
+	}
+
+	bool IsStarting() const {
+		return state == DecoderState::START;
+	}
+
+	gcc_pure
+	bool LockIsStarting() const {
+		Lock();
+		bool result = IsStarting();
+		Unlock();
+		return result;
+	}
+
+	bool HasFailed() const {
+		assert(command == DecoderCommand::NONE);
+
+		return state == DecoderState::ERROR;
+	}
+
+	gcc_pure
+	bool LockHasFailed() const {
+		Lock();
+		bool result = HasFailed();
+		Unlock();
+		return result;
+	}
+
+	/**
+	 * Checks whether an error has occurred, and if so, returns a
+	 * copy of the #Error object.
+	 *
+	 * Caller must lock the object.
+	 */
+	gcc_pure
+	Error GetError() const {
+		assert(command == DecoderCommand::NONE);
+		assert(state != DecoderState::ERROR || error.IsDefined());
+
+		Error result;
+		if (state == DecoderState::ERROR)
+			result.Set(error);
+		return result;
+	}
+
+	/**
+	 * Like dc_get_error(), but locks and unlocks the object.
+	 */
+	gcc_pure
+	Error LockGetError() const {
+		Lock();
+		Error result = GetError();
+		Unlock();
+		return result;
+	}
+
+	/**
+	 * Clear the error condition and free the #Error object (if any).
+	 *
+	 * Caller must lock the object.
+	 */
+	void ClearError() {
+		if (state == DecoderState::ERROR) {
+			error.Clear();
+			state = DecoderState::STOP;
+		}
+	}
+
+	/**
+	 * Check if the specified song is currently being decoded.  If the
+	 * decoder is not running currently (or being started), then this
+	 * function returns false in any case.
+	 *
+	 * Caller must lock the object.
+	 */
+	gcc_pure
+	bool IsCurrentSong(const DetachedSong &_song) const;
+
+	gcc_pure
+	bool LockIsCurrentSong(const DetachedSong &_song) const {
+		Lock();
+		const bool result = IsCurrentSong(_song);
+		Unlock();
+		return result;
+	}
+
+private:
+	/**
+	 * Wait for the command to be finished by the decoder thread.
+	 *
+	 * To be called from the client thread.  Caller must lock the
+	 * object.
+	 */
+	void WaitCommandLocked() {
+		while (command != DecoderCommand::NONE)
+			WaitForDecoder();
+	}
+
+	/**
+	 * Send a command to the decoder thread and synchronously wait
+	 * for it to finish.
+	 *
+	 * To be called from the client thread.  Caller must lock the
+	 * object.
+	 */
+	void SynchronousCommandLocked(DecoderCommand cmd) {
+		command = cmd;
+		Signal();
+		WaitCommandLocked();
+	}
+
+	/**
+	 * Send a command to the decoder thread and synchronously wait
+	 * for it to finish.
+	 *
+	 * To be called from the client thread.  This method locks the
+	 * object.
+	 */
+	void LockSynchronousCommand(DecoderCommand cmd) {
+		Lock();
+		ClearError();
+		SynchronousCommandLocked(cmd);
+		Unlock();
+	}
+
+	void LockAsynchronousCommand(DecoderCommand cmd) {
+		Lock();
+		command = cmd;
+		Signal();
+		Unlock();
+	}
+
+public:
+	/**
+	 * Start the decoder.
+	 *
+	 * @param song the song to be decoded; the given instance will be
+	 * owned and freed by the decoder
+	 * @param start_ms see #DecoderControl
+	 * @param end_ms see #DecoderControl
+	 * @param pipe the pipe which receives the decoded chunks (owned by
+	 * the caller)
+	 */
+	void Start(DetachedSong *song, unsigned start_ms, unsigned end_ms,
+		   MusicBuffer &buffer, MusicPipe &pipe);
+
+	void Stop();
+
+	bool Seek(double where);
+
+	void Quit();
+
+	const char *GetMixRampStart() const {
+		return mix_ramp.GetStart();
+	}
+
+	const char *GetMixRampEnd() const {
+		return mix_ramp.GetEnd();
+	}
+
+	const char *GetMixRampPreviousEnd() const {
+		return previous_mix_ramp.GetEnd();
+	}
+
+	void SetMixRamp(MixRampInfo &&new_value) {
+		mix_ramp = std::move(new_value);
+	}
+
+	/**
+	 * Move mixramp_end to mixramp_prev_end and clear
+	 * mixramp_start/mixramp_end.
+	 */
+	void CycleMixRamp();
+};
+
+#endif