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.
+  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);
+};
+