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diff --git a/src/lib/packet_queue.h b/src/lib/packet_queue.h
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+/*
+    Copyright (C) 2026 Carl Hetherington <cth@carlh.net>
+
+    This file is part of DCP-o-matic.
+
+    DCP-o-matic 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.
+
+    DCP-o-matic 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 DCP-o-matic.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+
+#ifndef DCPOMATIC_PACKET_QUEUE_H
+#define DCPOMATIC_PACKET_QUEUE_H
+
+
+/** @file  src/lib/packet_queue.h
+ *  @brief PacketQueue parent class.
+ */
+
+
+#include <boost/optional.hpp>
+#include <boost/variant.hpp>
+#include <cstdint>
+#include <deque>
+
+struct AVPacket;
+
+
+/** @class PacketQueue
+ *  @brief Parent class for things which take and then return AVPackets, possibly
+ *  re-ordering them.
+ */
+class PacketQueue
+{
+public:
+	virtual ~PacketQueue() = default;
+
+	enum class Type {
+		VIDEO,
+		AUDIO,
+		SUBTITLE,
+		DROP,
+	};
+
+	/** Container for the only information we need to keep from a DROP packet */
+	struct PacketInfo {
+		PacketInfo(AVPacket* packet);
+
+		int stream_index;
+		int64_t dts;
+	};
+
+	typedef boost::variant<AVPacket*, PacketInfo> Packet;
+
+	/** Add a packet to the queue.  Does not ref the packet; we expect
+	 *  the packet to be freed when it comes out of get() (or by clear()).
+	 */
+	virtual void add(AVPacket* packet, Type type) = 0;
+
+	/** Get the next packet to process.
+	 *  @param flushing should be true if we are flushing at the end of a decode.
+	 *  When this is true the queue will be emptied without trying to re-order it.
+	 *  Returns boost::none when there are no more packets to get.
+	 */
+	virtual boost::optional<std::pair<Packet, Type>> get(bool flushing) = 0;
+
+	/** Clear the queue.  Packets will be freed. */
+	virtual void clear() = 0;
+};
+
+
+#endif
+