[PPAPI] Implement media stream video track API

ppapi/shared_impl/media_stream_frame.h

+// Copyright (c) 2014 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 PPAPI_SHARED_IMPL_MEDIA_STREAM_FRAME_H_
+#define PPAPI_SHARED_IMPL_MEDIA_STREAM_FRAME_H_
+
+#include <string>
+
+#include "ppapi/c/ppb_video_frame.h"
+
+namespace ppapi {
+
+union MediaStreamFrame {
+  enum Type {
+    TYPE_UNKNOWN = 0,
+    TYPE_AUDIO = 1,
+    TYPE_VIDEO = 2,
+  };
+
+  struct Header {
+    Type type;
+    uint32_t size;
+  };
+
+  struct Audio {
+    Header header;
+    // TODO(penghuang): implement the audio frame.
+  };
+
+  struct Video {
+    Header header;
+    PP_TimeDelta timestamp;
+    PP_VideoFrame_Format format;
+    PP_Size size;
+    uint32_t data_size;
+    uint8_t data[1];
+  };
+
+  Header header;
+  Video video;
+  Audio audio;

[dmichael (off chromium), 2014/01/09 21:06:47]

I think you need to add compile assertions to enforce the size of each type you
put in the shared memory region. Everything you put in there is implicitly part
of your IPC contract. In the case of NaCl, the plugin-side of the proxy is built
using a different toolchain (always using the ILP32 ABI). This can lead to
differences in size & alignment between plugin and renderer, for some
structures. So you should assert here, document the reason. If they *don't*
match, you may have to add some padding somewhere to force them to match.

[Peng, 2014/01/10 19:14:30]

Done.

+};
+
+}  // namespace ppapi
+
+#endif  // PPAPI_SHARED_IMPL_MEDIA_STREAM_FRAME_H_