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diff --git a/src/output_plugin.h b/src/output_plugin.h
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+++ b/src/output_plugin.h
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+/*
+ * Copyright (C) 2003-2009 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#ifndef MPD_OUTPUT_PLUGIN_H
+#define MPD_OUTPUT_PLUGIN_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+struct audio_output;
+struct config_param;
+struct audio_format;
+struct tag;
+
+/**
+ * A plugin which controls an audio output device.
+ */
+struct audio_output_plugin {
+	/**
+	 * the plugin's name
+	 */
+	const char *name;
+
+	/**
+	 * Test if this plugin can provide a default output, in case
+	 * none has been configured.  This method is optional.
+	 */
+	bool (*test_default_device)(void);
+
+	/**
+	 * Configure and initialize the device, but do not open it
+	 * yet.
+	 *
+	 * @param ao an opaque pointer to the audio_output structure
+	 * @param audio_format the configured audio format, or NULL if
+	 * none is configured
+	 * @param param the configuration section, or NULL if there is
+	 * no configuration
+	 * @return NULL on error, or an opaque pointer to the plugin's
+	 * data
+	 */
+	void *(*init)(struct audio_output *ao,
+		      const struct audio_format *audio_format,
+		      const struct config_param *param);
+
+	/**
+	 * Free resources allocated by this device.
+	 */
+	void (*finish)(void *data);
+
+	/**
+	 * Really open the device.
+	 * @param audio_format the audio format in which data is going
+	 * to be delivered; may be modified by the plugin
+	 */
+	bool (*open)(void *data, struct audio_format *audio_format);
+
+	/**
+	 * Play a chunk of audio data.
+	 */
+	bool (*play)(void *data, const char *playChunk, size_t size);
+
+	/**
+	 * Pause the device.  If supported, it may perform a special
+	 * action, which keeps the device open, but does not play
+	 * anything.  Output plugins like "shout" might want to play
+	 * silence during pause, so their clients won't be
+	 * disconnected.  Plugins which do not support pausing will
+	 * simply be closed, and have to be reopened when unpaused.
+	 *
+	 * @return false on error (output will be closed then), true
+	 * for continue to pause
+	 */
+	bool (*pause)(void *data);
+
+	/**
+	 * Try to cancel data which may still be in the device's
+	 * buffers.
+	 */
+	void (*cancel)(void *data);
+
+	/**
+	 * Close the device.
+	 */
+	void (*close)(void *data);
+
+	/**
+	 * Control the device. Usualy used for implementing
+	 * set and get mixer levels
+	 */
+	bool (*control)(void *data, int cmd, void *arg);
+
+	/**
+	 * Display metadata for the next chunk.  Optional method,
+	 * because not all devices can display metadata.
+	 */
+	void (*send_tag)(void *data, const struct tag *tag);
+};
+
+#endif