Add audio_device_id in mojo media ServiceFactory CreateRenderer api.

media/mojo/interfaces/service_factory.mojom

Index: media/mojo/interfaces/service_factory.mojom
diff --git a/media/mojo/interfaces/service_factory.mojom b/media/mojo/interfaces/service_factory.mojom
index b55e284c226d2b321e52f0344897742237d34bd4..0ef1445753ce3e6785c0716ad70b0fe527dad21a 100644
--- a/media/mojo/interfaces/service_factory.mojom
+++ b/media/mojo/interfaces/service_factory.mojom
@@ -19,7 +19,11 @@ interface ServiceFactory {
   CreateVideoDecoder(VideoDecoder& video_decoder);
 
   // Creates a Renderer service.
-  CreateRenderer(Renderer& renderer);
+  // Audio stream will be played on device_id, which is defined in
+  // media/audio/audio_device_description.h. If audio_device_id
+  // is empty, kDefaultDeviceId will be used. 

[dcheng, 2016/06/03 04:29:48]

Is the device_id structured data of any kind? Or is it an opaque handle? What is
a Renderer service? I looked at renderer.mojom but there's no comments on the
interface...

What process does ServiceFactory live in? And who calls into ServiceFactory?

[xhwang, 2016/06/03 04:53:28]

device_id is just a string. See dalecurtis's explanation here:
https://codereview.chromium.org/2016053003/#msg18
A Renderer service is the mojo version of media::Renderer interface:
https://code.google.com/p/chromium/codesearch#chromium/src/media/base/rendere...

Basically it reads demuxed compressed audio/video buffers, and try to decode
them and render them.

Agreed that documentation can be improved.
ServiceFactory implementation lives in the process where these services (CDM,
Renderer, etc) are provided. Based on different configuration, this process
could be the Browser process, GPU process or Utility process. In the ChromeCast
case, it's in the Browser process but they do plan to move it to the Utility
process in the future. Note that currently the ChromeCast media pipeline is
living in the Browser process as well. So the current work is mostly replace IPC
with mojo without changing the process model.

ServiceFactory typically will be called by the Render process, where the media
pipeline in Render frames lives. In this particular case, it'll be called by
some ChromeCast code in the utility process. tianyuwang@ will know more details.

[tianyuwang1, 2016/06/03 18:31:50]

On ChromeCast, ServiceFactory is called by Renderer process as Xiaohan
mentioned.  ServiceFactory will also be called from the utility process in order
to play audio.

+  CreateRenderer(Renderer& renderer,
+                 string audio_device_id);
 
   // Creates a ContentDecryptionModule service.
   CreateCdm(ContentDecryptionModule& cdm);