Video Capture Mojo Component: Skeleton

device/video/video_capture_device_factory.mojom

+// Copyright 2016 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.
+
+module device.mojom;
+
+import "device/video/video_capture_device.mojom";
+import "device/video/video_capture_format.mojom";
+
+enum VideoCaptureApi {
+  LINUX_V4L2_SINGLE_PLANE,
+  WIN_MEDIA_FOUNDATION,
+  WIN_DIRECT_SHOW,
+  MACOSX_AVFOUNDATION,
+  MACOSX_DECKLINK,
+  ANDROID_API1,
+  ANDROID_API2_LEGACY,
+  ANDROID_API2_FULL,
+  ANDROID_API2_LIMITED,
+  ANDROID_TANGO,
+  UNKNOWN
+};
+
+enum VideoCaptureTransportType {
+  // For AVFoundation Api, identify devices that are built-in or USB.
+  MACOSX_USB_OR_BUILT_IN,
+  OTHER_TRANSPORT
+};
+
+struct VideoCaptureDeviceDescriptor {
+  string display_name;
+  string device_id;
+  string model_id;
+  VideoCaptureApi capture_api;
+  VideoCaptureTransportType transport_type;
+};
+
+interface VideoCaptureDeviceFactory {

[Ken Rockot(use gerrit already), 2016/08/02 22:46:25]

nit: VideoCaptureDeviceProvider? I don't think "factory" is quite accurate

[chfremer, 2016/08/03 22:14:15]

I feel the term "Factory" is correct here in a sense that it creates instances
of VideoCaptureDevice, which in turn represent access to a physical device. Is
your concern that it could be understood to mean that it creates actual devices?

Note, that we may later want to include "virtual" capture devices that capture
screens, windows, or tabs.

+  EnumerateDeviceDescriptors()
+    => (array<VideoCaptureDeviceDescriptor> descriptors);

[Ken Rockot(use gerrit already), 2016/08/02 22:46:25]

nit: +4 space indent for line continuations.

[chfremer, 2016/08/03 22:14:14]

Done.

+
+  GetSupportedFormats(VideoCaptureDeviceDescriptor device_descriptor)
+    => (array<VideoCaptureFormat> supported_formats);
+
+  CreateDevice(VideoCaptureDeviceDescriptor device_descriptor)

[Ken Rockot(use gerrit already), 2016/08/02 22:46:25]

Idiomatic mojom would be

  CreateDevice(VideoCaptureDeviceDescriptor descriptor,
               VideoCaptureDevice& device_request);

with no response. Then the client can create its own pipe and use it
immediately, like:

  VideoCaptureDevicePtr device;
  provider->CreateDevice(std::move(descriptor), mojo::GetProxy(&device));
  device->Start(format, policy, frequency);

The actual IPC corresponding to Start will be sent in parallel immediately after
the one corresponding to CreateDevice. No need to write async code or wait for a
round-trip.

[chfremer, 2016/08/03 22:14:14]

Thanks. That is really smart and I wouldn't have thought of it.

+    => (VideoCaptureDevice device);
+};