media: add basic MediaRenderer mojom and TypeConverters

media/mojo/interfaces/media_renderer.mojom

+// Copyright 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.
+
+import "media/mojo/interfaces/media_types.mojom"
+
+module mojo {
+
+[Client=MediaRendererClient]
+interface MediaRenderer {
+  // Initializes the Renderer, calling back with status upon completion.
+  Initialize() => (bool succeeded);

[xhwang, 2014/09/03 00:09:08]

FYI: The callback can be a closure after
https://codereview.chromium.org/526653002/ is landed.

[tim (not reviewing), 2014/09/03 00:43:50]

Acknowledged.

+
+  // Decode and render |buffer|, calling back when more data is required.

[xhwang, 2014/09/03 00:09:08]

nit: Decode_s_ and render_s_

[tim (not reviewing), 2014/09/03 00:43:50]

OK, Done.

+  // TODO(tim): Switch decoding model to use framed data pipe when available.
+  // In that world, the signalling for more would be implicit by a writable
+  // pipe handle on the client side so this entire method + callback goes away.
+  DecodeAndRender(MediaDecoderBuffer buffer) => ();
+
+  // Discards any buffered data, executing callback when completed.

[xhwang, 2014/09/03 00:09:08]

nit: Add something like "Fires OnError() before the callback if error happened."

[tim (not reviewing), 2014/09/03 00:43:50]

Done.

+  Flush() => ();
+
+  // Starts rendering from |time|.

[xhwang, 2014/09/03 00:09:08]

nit: s/time/time_usec

[tim (not reviewing), 2014/09/03 00:43:50]

Done.

+  StartPlayingFrom(int64 time_delta_usec);

[scherkus (not reviewing), 2014/09/02 23:50:19]

does mojo have any equivalent time types?

[xhwang, 2014/09/03 00:09:08]

nit: s/time_delta_usec/time_usec?

[tim (not reviewing), 2014/09/03 00:43:50]

Done.

[tim (not reviewing), 2014/09/03 00:43:50]

No. I asked the same question to either Darin or Trung when writing
TestTimeService (https://codereview.chromium.org/349303006) and it wasn't
something we wanted to add. I'm not sure I remember why aside from probably
"seems like extra bells and whistles we don't need (yet)"...

+
+  // Updates the current playback rate. The default playback rate should be 1.
+  SetPlaybackRate(float playback_rate);
+  
+  // Sets the output volume. The default volume should be 1.
+  SetVolume(float volume);
+};
+
+interface MediaRendererClient {
+  // Called whenever rendering has advanced time by |time_delta_usec|.

[xhwang, 2014/09/03 00:09:08]

nit: How about "Called to report media time advance of |time_delta_usec|"?

"whenever" is a bit misleading here since the caller decides when to call.

[tim (not reviewing), 2014/09/03 00:43:49]

Agreed, done.

+  OnTimeUpdate(int64 time_delta_usec);
+
+  // Called to report buffering state changes, see media_types.mojom.
+  OnBufferingStateChange(BufferingState state);
+
+  // Executed when rendering has reached the end of stream.
+  OnEnded();
+
+  // Executed if any error was encountered during decode or rendering.

[xhwang, 2014/09/03 00:09:08]

nit: If this error happens during an operation that has a completion callback,
call OnError() before firing the completion callback.

[tim (not reviewing), 2014/09/03 00:43:50]

Done.

+  OnError();
+};
+
+}  // module mojo