[camera][draft] Add camera plugin (#29)

Added the first draft version, but there are still a lot of unimplemented features.

packages/camera/elinux/camera_stream_handler.h

@@ -0,0 +1,32 @@
+// Copyright 2021 Sony Group Corporation. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PACKAGES_CAMERA_CAMERA_ELINUX_CAMERA_STREAM_HANDLER_H_
+#define PACKAGES_CAMERA_CAMERA_ELINUX_CAMERA_STREAM_HANDLER_H_
+
+class CameraStreamHandler {
+ public:
+  CameraStreamHandler() = default;
+  virtual ~CameraStreamHandler() = default;
+
+  // Prevent copying.
+  CameraStreamHandler(CameraStreamHandler const&) = delete;
+  CameraStreamHandler& operator=(CameraStreamHandler const&) = delete;
+
+  // Notifies the completion of initializing the video player.
+  void OnNotifyInitialized() { OnNotifyInitializedInternal(); }
+
+  // Notifies the completion of decoding a video frame.
+  void OnNotifyFrameDecoded() { OnNotifyFrameDecodedInternal(); }
+
+  // Notifies the completion of playing a video.
+  void OnNotifyCompleted() { OnNotifyCompletedInternal(); }
+
+ protected:
+  virtual void OnNotifyInitializedInternal() = 0;
+  virtual void OnNotifyFrameDecodedInternal() = 0;
+  virtual void OnNotifyCompletedInternal() = 0;
+};
+
+#endif  // PACKAGES_CAMERA_CAMERA_ELINUX_CAMERA_STREAM_HANDLER_H_