chromeos/services/tts/public/mojom/tts_service.mojom

// Copyright 2020 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 chromeos.tts.mojom;

import "services/audio/public/mojom/stream_factory.mojom";

// The main interface to the TTS engine on Chrome OS. Only used by and private
// to the Chrome OS Google TTS engine component extension. TtsService lives in a
// tts-sandboxed process.  TtsEngineExtensionObserver, the other end of this
// interface, in the browser process, brokers a connection between TtsService
// and the Google TTS engine component extension through a TtsStream, but does
// not participate otherwise.
interface TtsService {
  // Binds a TtsStream to this service and returns an AudioOutputStream receiver
  // which this service uses to play audio.
  BindTtsStream(pending_receiver<TtsStream> receiver,
                pending_remote<audio.mojom.StreamFactory> stream_factory);
};

// Interface for the Google component TTS engine to control
// the TtsService's production of audio. There is only ever one TtsStream
// owned by the TtsService.
//
// The component extension sets up the stream's voice by doing:
// InstallVoice(data, "voice")
// InstallVoice(other_data, "other_voice")
// SelectVoice("other_voice")
//
// After speaking using the stream (see below), the component extension can do:
// SelectVoice("voice")
// to change voices.
//
// The component extension calls the following two methods repeatedly and
// optionally observes events.
//
// Speak(<a proto containing text "Hello there.">)
// Speak(<proto containing text "Testing 1, 2, 3.")
// Stop()
//
// Note that the component extension may call Stop() early, if the TTS api
// wants to, for example, stop speech.
interface TtsStream {
  // Forward and install the |voice_name| encoded by |voice_bytes|.
  InstallVoice(string voice_name, array<uint8> voice_bytes)
      => (bool success);

  // Selects a voice for streaming given a |voice_name|.
  SelectVoice(string voice_name) => (bool success);

  // Speak text described by a serialized proto.speech.tts.Text proto.
  Speak(array<uint8> text_jspb)
      => (pending_receiver<TtsEventObserver> event_observer);

  // Stop speaking the currently speaking text, if any.
  Stop();

  // Sets the volume of the tts playback (0.0 to 1.0).
  SetVolume(float volume);
};

// Returned to callers of TtsStream.speak(). It receives notable events
// pertaining to the text spoken.
interface TtsEventObserver {
  // TtsStream.Speak started speech playback.
  OnStart();

  // TtsStream.Speak is playing text at |char_index| approximately at the
  // current time.
  OnTimepoint(int32 char_index);

  // TtsStream.Speak ended speech playback.
  OnEnd();

  // TtsStream.Speak encountered an error.
  OnError();
};