Implement the Co-Doing API

This page describes how to use the Co-Doing API to support a co-doing scenario.

Note: To do this properly requires effort to address several edge cases around latency and other delays. The following examples address some use cases in the co-doing scenario.

Initial setup

Similar to the Co-Watching initial setup, the following example shows a basic initialization use case:

Java

class AwesomeVideoAddonSessionHandler implements AddonSessionHandler {}

// For sample implementation, see the "Manage current state" section below.
class AwesomeVideoCoDoingHandler implements CoDoingHandler {}

public ListenableFuture<AddonSession> initialSetup() {
  AddonClient meetClient = AddonClientFactory.getClient();
  return meetClient
      .newSessionBuilder(
          /* liveSharingApplicationName= */ "awesome-video-app",
          appContext,
          new AwesomeVideoAddonSessionHandler())
      .withCoDoing(new AwesomeVideoCoDoingHandler())
      .begin();
}

Pause video

When participating in a live sharing experience, if a user pauses the playback on their local video app then presumably you'll likely want to make sure all participants in the live sharing experience also pause their video.

To do this, craft a CoDoingState message showing the video is paused, and tell Meet to broadcast it all other live sharing participants:

Java

public void onVideoPaused(String videoUrl, Instant currentTimestamp) {
  // Create an internal state object to share with other participants. Note: It's
  // good practice to encode all metadata—even seemingly irrelevant data—into
  // ActivityState updates to guard against race conditions and other subtle
  // failures.
  AwesomeVideoState videoState = AwesomeVideoState
    .builder()
    .videoUrl(videoUrl)
    .videoTimestamp(currentTimestamp)
    .isPaused(true)
    .build();

  // Create the CoDoingState object to wrap the internal state
  CoDoingState coDoingState = new CoDoingState();
  coDoingState.state = SerializationUtils.serialize(videoState);

  // Use Meet to broadcast internal state update to all other participants
  this.coDoingClient.setGlobalState(coDoingState);
};

The above code triggers the serialized VideoState object to be broadcast to all other instances of Meet currently participating in the live sharing experience. For details on how to receive broadcast updates from other participants, see the Handle incoming updates section below.

The following sequence diagram describes the sequence of events after the pause action is triggered:

Unpause video

Similar to pause, if a user unpauses the video on their local app Meet needs to broadcast this operation to other live sharing participants.

On the sender side (the user who unpauses the video) the only difference from the pause example is the isPaused status is updated. The sender side code should look like this:

Java

public void onVideoUnpaused(String videoUrl, Instant currentTimestamp) {
  AwesomeVideoState videoState = AwesomeVideoState
    .builder()
    .videoUrl(videoUrl)
    .videoTimestamp(currentTimestamp)
    .isPaused(false)
    .build();

  CoDoingState coDoingState = new CoDoingState();
  coDoingState.state = SerializationUtils.serialize(videoState);

  this.coDoingClient.setGlobalState(coDoingState);
}

Seek video

When a user drags the timeline on the local app to a new timestamp, we want to broadcast this operation to all participants similar to the pause and unpause sections. The sender side code looks like this:

Java

public void onVideoSeeked(String videoUrl, Instant currentTimestamp, bool isPaused) {
  AwesomeVideoState videoState = AwesomeVideoState
    .builder()
    .videoUrl(videoUrl)
    .videoTimestamp(currentTimestamp)
    .isPaused(isPaused)
    .build();

  CoDoingState coDoingState = new CoDoingState();
  coDoingState.state = SerializationUtils.serialize(videoState);

  this.coDoingClient.setGlobalState(coDoingState);
}

Play a different video

If the user also changes the video being watched by selecting another video on the local app, we need to play the new video for all live sharing participants. The change in video is held in VideoState.videoUrl:

Java

public void onVideoChanged(String videoUrl, Duration currentTimestamp, bool isPaused) {
  AwesomeVideoState videoState = AwesomeVideoState
    .builder()
    .videoUrl(videoUrl)
    .videoTimestamp(currentTimestamp)
    .isPaused(isPaused)
    .build();

  CoDoingState coDoingState = new CoDoingState();
  coDoingState.state = SerializationUtils.serialize(videoState);

  this.coDoingClient.setGlobalState(coDoingState);
}

End co-doing

When the user selects "stop live sharing,” we need to end their live sharing experience.

After the library is called to end the meeting, the live sharing app can quit or go back to its homepage (depending on the product’s preference).

Java

public void endCoDoing() {
  this.session.endSession();
}

Handle incoming updates

When another participant’s Meet app receives a broadcast, the onGlobalStateChanged() callback is triggered. Usually, it's important to make good decisions on what action to take in response to incoming updates such as only matching incoming video timestamps if they're sufficiently different from the local timestamp.

Java

class AwesomeVideoCoDoingHandler implements CoDoingHandler {
  public void onGlobalStateChanged(CoDoingState update) {
    AwesomeVideoState videoState = SerializationUtils.deserialize(update.state());

    // Handle transition to new video.
    if (!videoState.videoUrl.equals(this.videoPlayer.videoUrl)) {
      this.videoPlayer.loadVideo(videoState.videoUrl);
    }

    // If the timestamp in the arriving update has sufficiently diverged, adjust
    // the local video playout.
    if (videoState.videoTimestamp.minus(this.videoPlayer.videoTimestamp).abs() >
                                        Duration.ofSeconds(2)) {
      this.videoPlayer.seek(videoState.videoTimestamp);
    }

    // Update pause state if necessary.
    if (!videoState.isPaused && this.videoPlayer.isPaused) {
      this.videoPlayer.unpause();
    } else if (videoState.isPaused && !this.videoPlayer.isPaused) {
      this.videoPlayer.pause();
    }
  }
}