content/common/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.

module content.mojom;

import "media/mojo/interfaces/media_types.mojom";
import "media/capture/mojo/video_capture_types.mojom";
import "ui/gfx/geometry/mojo/geometry.mojom";

// This file decribes the communication between a given Renderer Host interface
// implementation (VideoCaptureHost) and a remote VideoCaptureObserver.
// VideoCaptureHost offers a stateless part (GetDeviceSupportedFormats() and
// GetDeviceFormatsInUse()) that can be invoked at any time, and a stateful part
// sandwiched between Start() and Stop(). A Client's OnStateChanged() can be
// notified any time during the stateful part. The stateful part is composed of
// a preamble where a Renderer client sends a command to Start() the capture,
// registering itself as the associated remote VideoCaptureObserver. The Host
// will then create and pre- share a number of buffers:
//
//   Observer                                        VideoCaptureHost
//      | ---> StartCapture                                     |
//      |                        OnStateChanged(STARTED) <---   |
//      |                             OnBufferCreated(1) <---   |
//      |                             OnBufferCreated(2) <---   |
//      =                                                       =
// and capture will then refer to those preallocated buffers:
//      |                               OnBufferReady(1) <---   |
//      |                               OnBufferReady(2) <---   |
//      | ---> ReleaseBuffer(1)                                 |
//      |                               OnBufferReady(1) <---   |
//      | ---> ReleaseBuffer(2)                                 |
//      |                               OnBufferReady(2) <---   |
//      | ---> ReleaseBuffer(1)                                 |
//      |                         ...                           |
//      =                                                       =
// Buffers can be reallocated with a larger size, if e.g. resolution changes.
//      |                 (resolution change)                   |
//      |                           OnBufferDestroyed(1) <---   |
//      |                             OnBufferCreated(3) <---   |
//      |                               OnBufferReady(3) <---   |
//      | ---> ReleaseBuffer(2)                                 |
//      |                           OnBufferDestroyed(2) <---   |
//      |                             OnBufferCreated(5) <---   |
//      |                               OnBufferReady(5) <---   |
//      =                                                       =
// In the communication epilogue, the client Stop()s capture, receiving a last
// status update:
//      | ---> StopCapture                                      |
//      |                        OnStateChanged(STOPPED) <---   |

enum VideoCaptureState {
  STARTED,
  PAUSED,
  RESUMED,
  STOPPED,
  FAILED,
  ENDED,
};

// Interface for notifications from Browser/Host back to Renderer/Client. This
// interface is used between VideoCaptureHost.Start() and Stop().
interface VideoCaptureObserver {
  // Gets notified about a VideoCaptureState update.
  OnStateChanged(VideoCaptureState state);

  // A new buffer identified by |buffer_id| has been created for video capture.
  OnBufferCreated(int32 buffer_id, handle<shared_buffer> handle_fd);

  // |buffer_id| has video capture data with |info| containing the associated
  // VideoFrame constituent parts.
  OnBufferReady(int32 buffer_id, media.mojom.VideoFrameInfo info);

  // |buffer_id| has been released by VideoCaptureHost and must not be used.
  OnBufferDestroyed(int32 buffer_id);
};

interface VideoCaptureHost {
  // Start the |session_id| session with |params|. The video capture will be
  // identified as |device_id|, a new id picked by the renderer process.
  // |observer| will be used for notifications.
  Start(int32 device_id, int32 session_id, media.mojom.VideoCaptureParams params,
        VideoCaptureObserver observer);

  // Closes the video capture specified by |device_id|.
  Stop(int32 device_id);

  // Pauses the video capture specified by |device_id|.
  Pause(int32 device_id);

  // Resume |device_id| video capture, in |session_id| and with |params|.
  Resume(int32 device_id, int32 session_id, media.mojom.VideoCaptureParams params);

  // Requests that the video capturer send a frame "soon" (e.g., to resolve
  // picture loss or quality issues).
  RequestRefreshFrame(int32 device_id);

  // Indicates that a renderer has finished using a previously shared buffer.
  ReleaseBuffer(int32 device_id, int32 buffer_id,
                double consumer_resource_utilization);

  // Get the formats supported by a device referenced by |session_id|.
  GetDeviceSupportedFormats(int32 device_id, int32 session_id)
    => (array<media.mojom.VideoCaptureFormat> formats_supported);

  // Get the format(s) in use by a device referenced by |session_id|.
  GetDeviceFormatsInUse(int32 device_id, int32 session_id)
    => (array<media.mojom.VideoCaptureFormat> formats_in_use);
};