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diff --git a/cast/standalone_receiver/decoder.h b/cast/standalone_receiver/decoder.h
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+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CAST_STANDALONE_RECEIVER_DECODER_H_
+#define CAST_STANDALONE_RECEIVER_DECODER_H_
+
+#include <stdint.h>
+
+#include <string>
+#include <vector>
+
+#include "absl/types/span.h"
+#include "cast/standalone_receiver/avcodec_glue.h"
+#include "cast/streaming/frame_id.h"
+
+namespace openscreen {
+namespace cast {
+
+// Wraps libavcodec to decode audio or video.
+class Decoder {
+ public:
+  // A buffer backed by storage that is compatible with FFMPEG (i.e., includes
+  // the required zero-padding).
+  class Buffer {
+   public:
+    Buffer();
+    ~Buffer();
+
+    void Resize(int new_size);
+    absl::Span<const uint8_t> GetSpan() const;
+    absl::Span<uint8_t> GetSpan();
+
+   private:
+    std::vector<uint8_t> buffer_;
+  };
+
+  // Interface for receiving decoded frames and/or errors.
+  class Client {
+   public:
+    virtual ~Client();
+
+    virtual void OnFrameDecoded(FrameId frame_id, const AVFrame& frame) = 0;
+    virtual void OnDecodeError(FrameId frame_id, std::string message) = 0;
+    virtual void OnFatalError(std::string message) = 0;
+
+   protected:
+    Client();
+  };
+
+  // |codec_name| should be the codec_name field from an OFFER message.
+  explicit Decoder(const std::string& codec_name);
+  ~Decoder();
+
+  Client* client() const { return client_; }
+  void set_client(Client* client) { client_ = client; }
+
+  // Starts decoding the data in |buffer|, which should be associated with the
+  // given |frame_id|. This will synchronously call Client::OnFrameDecoded()
+  // and/or Client::OnDecodeError() zero or more times with results. Note that
+  // some codecs will have data dependencies that require multiple encoded
+  // frame's data before the first decoded frame can be generated.
+  void Decode(FrameId frame_id, const Buffer& buffer);
+
+ private:
+  // Helper to initialize the FFMPEG decoder and supporting objects. Returns
+  // false if this failed (and the Client was notified).
+  bool Initialize();
+
+  // Helper to get the FrameId that is associated with the next frame coming out
+  // of the FFMPEG decoder.
+  FrameId DidReceiveFrameFromDecoder();
+
+  // Helper to handle a codec initialization error and notify the Client of the
+  // fatal error.
+  void HandleInitializationError(const char* what, int av_errnum);
+
+  // Called when any transient or fatal error occurs, generating an Error and
+  // notifying the Client of it.
+  void OnError(const char* what, int av_errnum, FrameId frame_id);
+
+  const std::string codec_name_;
+  AVCodec* codec_ = nullptr;
+  AVCodecParserContextUniquePtr parser_;
+  AVCodecContextUniquePtr context_;
+  AVPacketUniquePtr packet_;
+  AVFrameUniquePtr decoded_frame_;
+
+  Client* client_ = nullptr;
+
+  // Queue of frames that have been input to the libavcodec decoder, but which
+  // have not yet had output generated by it.
+  std::vector<FrameId> frames_decoding_;
+};
+
+}  // namespace cast
+}  // namespace openscreen
+
+#endif  // CAST_STANDALONE_RECEIVER_DECODER_H_