Mojo Video Capture service in media/capture

media/capture/interfaces/video_capture.mojom

Index: media/capture/interfaces/video_capture.mojom
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+// 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
+// VideoCaptureStream, which is then Start()ed to produce FrameInfos to a
+// VideoCaptureStreamClient. In this sense, this API mimics a UserMediaClient.
+
+module media.mojom;
+
+import "media/mojo/interfaces/media_types.mojom";
+import "ui/mojo/geometry/geometry.mojom";
+
+struct VideoCaptureDeviceInfo {
+  string device_id;
+  string name;
+  // TODO(mcasas): add VideoFacingMode facing_mode;
+};
+
+struct VideoCaptureOptions {
+  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 any impact
+  // in 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 VideoCaptureStream.
+interface VideoCaptureStreamClient {
+  // Informs the client that new frame data is available. |info| provides
+  // details about this individual frame.
+  OnFrameAvailable(FrameInfo info) => ();
+
+  // An error has ocurred; the capture will in all likelihood be interrupted.

[perkj_chrome, 2016/03/07 23:58:27]

So to continu the discussion. What is the client supposed to do when this method
is called?  ie Should the end result be that the track state is changed to ended
in js? If so - I think this comment should make it clear that this client will
no longer be usable after this have happened. If I understand the
implementation, that is what happens ?

[mcasas, 2016/03/08 23:57:28]

Yes, you're right. Corrected.

+  OnError(string error);
+};
+
+// The VideoCaptureStream interface abstracts a distinct local source of video
+// frame data such as a WebCam.
+// TODO(mcasas): Consider extending to desktop capture and web view capture.
+interface VideoCaptureStream {
+  // Starts sending frames to |client|. Must only be called once and must be the
+  // first call on the Stream.
+  Start(VideoCaptureStreamClient client);
+
+  // Stops the capture, releasing all associated resources.
+  Stop();
+};
+
+// Primary top-level service interface exposed by the video_capture component.
+interface VideoCaptureHandler {
+  EnumerateDevices()
+      => (array<VideoCaptureDeviceInfo> devices);
+
+  // TODO(mcasas): Add a method to retrieve the capture capabilities of a given
+  // |device_id|.
+
+  RequestVideoCaptureStream(VideoCaptureOptions options)
+      => (VideoCaptureStream? stream);
+};
+