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diff --git a/src/encoder/EncoderInterface.hxx b/src/encoder/EncoderInterface.hxx
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+++ b/src/encoder/EncoderInterface.hxx
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+/*
+ * Copyright (C) 2003-2015 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_ENCODER_INTERFACE_HXX
+#define MPD_ENCODER_INTERFACE_HXX
+
+#include "EncoderPlugin.hxx"
+
+#include <assert.h>
+
+struct Encoder {
+	const EncoderPlugin &plugin;
+
+#ifndef NDEBUG
+	bool open, pre_tag, tag, end;
+#endif
+
+	explicit Encoder(const EncoderPlugin &_plugin)
+		:plugin(_plugin)
+#ifndef NDEBUG
+		, open(false)
+#endif
+	{}
+
+
+	/**
+	 * Frees an #Encoder object.
+	 */
+	void Dispose() {
+		assert(!open);
+
+		plugin.finish(this);
+	}
+
+	/**
+	 * Opens the object.  You must call this prior to using it.
+	 * Before you free it, you must call Close().  You may open
+	 * and close (reuse) one encoder any number of times.
+	 *
+	 * After this function returns successfully and before the
+	 * first encoder_write() call, you should invoke
+	 * encoder_read() to obtain the file header.
+	 *
+	 * @param audio_format the encoder's input audio format; the plugin
+	 * may modify the struct to adapt it to its abilities
+	 * @return true on success
+	 */
+	bool Open(AudioFormat &audio_format, Error &error) {
+		assert(!open);
+
+		bool success = plugin.open(this, audio_format, error);
+#ifndef NDEBUG
+		open = success;
+		pre_tag = tag = end = false;
+#endif
+		return success;
+	}
+
+
+	/**
+	 * Closes the object.  This disables the encoder, and readies
+	 * it for reusal by calling Open() again.
+	 */
+	void Close() {
+		assert(open);
+
+		if (plugin.close != nullptr)
+			plugin.close(this);
+
+#ifndef NDEBUG
+		open = false;
+#endif
+	}
+};
+
+/**
+ * Ends the stream: flushes the encoder object, generate an
+ * end-of-stream marker (if applicable), make everything which might
+ * currently be buffered available by encoder_read().
+ *
+ * After this function has been called, the encoder may not be usable
+ * for more data, and only encoder_read() and Encoder::Close() can be
+ * called.
+ *
+ * @param encoder the encoder
+ * @return true on success
+ */
+static inline bool
+encoder_end(Encoder *encoder, Error &error)
+{
+	assert(encoder->open);
+	assert(!encoder->end);
+
+#ifndef NDEBUG
+	encoder->end = true;
+#endif
+
+	/* this method is optional */
+	return encoder->plugin.end != nullptr
+		? encoder->plugin.end(encoder, error)
+		: true;
+}
+
+/**
+ * Flushes an encoder object, make everything which might currently be
+ * buffered available by encoder_read().
+ *
+ * @param encoder the encoder
+ * @return true on success
+ */
+static inline bool
+encoder_flush(Encoder *encoder, Error &error)
+{
+	assert(encoder->open);
+	assert(!encoder->pre_tag);
+	assert(!encoder->tag);
+	assert(!encoder->end);
+
+	/* this method is optional */
+	return encoder->plugin.flush != nullptr
+		? encoder->plugin.flush(encoder, error)
+		: true;
+}
+
+/**
+ * Prepare for sending a tag to the encoder.  This is used by some
+ * encoders to flush the previous sub-stream, in preparation to begin
+ * a new one.
+ *
+ * @param encoder the encoder
+ * @return true on success
+ */
+static inline bool
+encoder_pre_tag(Encoder *encoder, Error &error)
+{
+	assert(encoder->open);
+	assert(!encoder->pre_tag);
+	assert(!encoder->tag);
+	assert(!encoder->end);
+
+	/* this method is optional */
+	bool success = encoder->plugin.pre_tag != nullptr
+		? encoder->plugin.pre_tag(encoder, error)
+		: true;
+
+#ifndef NDEBUG
+	encoder->pre_tag = success;
+#endif
+	return success;
+}
+
+/**
+ * Sends a tag to the encoder.
+ *
+ * Instructions: call encoder_pre_tag(); then obtain flushed data with
+ * encoder_read(); finally call encoder_tag().
+ *
+ * @param encoder the encoder
+ * @param tag the tag object
+ * @return true on success
+ */
+static inline bool
+encoder_tag(Encoder *encoder, const Tag &tag, Error &error)
+{
+	assert(encoder->open);
+	assert(!encoder->pre_tag);
+	assert(encoder->tag);
+	assert(!encoder->end);
+
+#ifndef NDEBUG
+	encoder->tag = false;
+#endif
+
+	/* this method is optional */
+	return encoder->plugin.tag != nullptr
+		? encoder->plugin.tag(encoder, tag, error)
+		: true;
+}
+
+/**
+ * Writes raw PCM data to the encoder.
+ *
+ * @param encoder the encoder
+ * @param data the buffer containing PCM samples
+ * @param length the length of the buffer in bytes
+ * @return true on success
+ */
+static inline bool
+encoder_write(Encoder *encoder, const void *data, size_t length,
+	      Error &error)
+{
+	assert(encoder->open);
+	assert(!encoder->pre_tag);
+	assert(!encoder->tag);
+	assert(!encoder->end);
+
+	return encoder->plugin.write(encoder, data, length, error);
+}
+
+/**
+ * Reads encoded data from the encoder.
+ *
+ * Call this repeatedly until no more data is returned.
+ *
+ * @param encoder the encoder
+ * @param dest the destination buffer to copy to
+ * @param length the maximum length of the destination buffer
+ * @return the number of bytes written to #dest
+ */
+static inline size_t
+encoder_read(Encoder *encoder, void *dest, size_t length)
+{
+	assert(encoder->open);
+	assert(!encoder->pre_tag || !encoder->tag);
+
+#ifndef NDEBUG
+	if (encoder->pre_tag) {
+		encoder->pre_tag = false;
+		encoder->tag = true;
+	}
+#endif
+
+	return encoder->plugin.read(encoder, dest, length);
+}
+
+/**
+ * Get mime type of encoded content.
+ *
+ * @return an constant string, nullptr on failure
+ */
+static inline const char *
+encoder_get_mime_type(Encoder *encoder)
+{
+	/* this method is optional */
+	return encoder->plugin.get_mime_type != nullptr
+		? encoder->plugin.get_mime_type(encoder)
+		: nullptr;
+}
+
+#endif