Mojo Video Capture service in media/capture

media/capture/interfaces/video_capture.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.
+
+// This mojom defines the interface for enumerating Video Capture Devices and
+// selecting one for capturing. Such a VCD is manipulated via creation of a
+// Stream, which is then Start()ed to produce FrameInfos to a StreamCient. In
+// this sense, this API mimics a UserMediaClient.
+
+module media.mojom;
+
+import "media/mojo/interfaces/media_types.mojom";
+import "ui/mojo/geometry/geometry.mojom";
+
+// Copies of third_party/WebKit/public/platform/WebSourceInfo.h.
+enum SourceKind { None, Audio, Video };
+enum VideoFacingMode { None, User, Environment };
+struct WebSourceInfo {
+  string device_id;
+  string label;
+
+  SourceKind kind;  // Should always be blink::WebSourceInfo::SourceKindVideo
+
+  VideoFacingMode facing_mode;
+};
+
+struct StreamOptions {
+  string device_id;
+
+  // Replicate the used fields of VideoCaptureParams.
+  mojo.Size capture_size;
+  double frame_rate;
+  // TODO(mcasas): add and wire PowerLineFrequency and ResolutionChangePolicy.
+};
+
+// Information provided to a VideoStreamClient about an available video frame.
+struct FrameInfo {
+  // Shared memory handle to allocated storage for the frame. This handle may
+  // be mapped by the client for read-only access.
+  // TODO(mcasas): investigate if sharing this buffer per frame has ny impact in

[perkj_chrome, 2016/03/02 13:14:10]

s ny/any

[mcasas, 2016/03/02 19:53:51]

Done.

+  // performance. If so, reinstaurate a sharing-buffer-preamble.
+  handle<shared_buffer> storage_handle;
+  // Size in bytes of the allocated storage.
+  int32 storage_size;
+
+  // Pixel format of the frame data in storage.
+  media.interfaces.VideoFormat pixel_format;
+
+  // Size of the frame in pixels. This includes pixel data for the whole image;
+  // i.e. for YUV formats with subsampled chroma planes where the visible
+  // portion does not line up on a sample boundary, |coded_size| will be rounded
+  // up appropriately and pixel data will be provided for the odd pixels.
+  mojo.Size coded_size;
+
+  // Visible rectangle of pixels in the frame. This must be a subrect of
+  // |coded_rect|. May be odd with respect to the sample boundaries, e.g. for
+  // formats with subsampled chroma. This is used e.g. for letterboxing.
+  mojo.Rect visible_rect;
+
+  // A coded version of base::TimeTicks::Now() at the time the frame data was
+  // generated by its source. For the sake of consistency this must always be
+  // interpreted using base::TimeTicks::FromInternalValue or some equivalent.
+  int64 timestamp;
+};
+
+// The client interface for a Stream.
+interface StreamClient {
+  // Informs the client that new frame data is available. |info| provides
+  // details about this individual frame.
+  FrameAvailable(FrameInfo info) => ();
+
+  // Some Error has happened; the capture will in all likelihood be interrupted.
+  Error(string error);
+};
+
+// The Stream interface abstracts a distinct local source of video frame data
+// such as a camera device, desktop capture, web view capture.
+interface Stream {
+  // Starts sending frames to |client|. Must only be called once and must be the
+  // first call on the Stream.
+  Start(StreamClient client);
+
+  // Temporarily stops sending frames to the client. The client will not begin
+  // receiving frame data again until Resume is called.
+  Pause();

[perkj_chrome, 2016/03/02 13:14:10]

Is  Pause used? Can we skip this for now and use Start Stop only? 

[mcasas, 2016/03/02 19:53:51]

Done.

+
+  // Resumes sending frames to the client.
+  Resume();
+
+  // Stops the capture, releasing all associated resources.
+  Stop();
+};
+
+// The primary top-level service interface exposed by the video_capture
+// component. This is used by a UserMediaClient implementation to get hold of a
+// Stream that can be Start()ed to produce video frames, so in a way, it is a
+// video-only flavour of WebUserMediaClient.
+// TODO(mcasas): Add a method to retrieve the capture capabilities of a given
+// |device_id|.
+interface VideoCaptureHandler {
+  // requestMediaDevices(const WebMediaDevicesRequest&)
+  RequestMediaDevices()
+      => (array<WebSourceInfo> devices);

[perkj_chrome, 2016/03/02 13:14:10]

should only be possible to get one video device at the time.

[mcasas, 2016/03/02 19:53:51]

? 

This RPC enumerates the devices, it follows the UserMediaClient
naming [1]

[1]
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

+
+  // requestUserMedia(const WebUserMediaRequest&)
+  RequestStream(StreamOptions options, string security_origin)

[perkj_chrome, 2016/03/02 13:14:10]

Can we stick with only one method to start with.

[mcasas, 2016/03/02 19:53:51]

Negative, we need at least:
- enumerate all devices
- start capturing using one of them
to have a prototype that actually does something.

+      => (Stream? stream);
+};
+