Text-to-speech destinations#

Text-to-speech (TTS) messages are injected to destinations. Destinations determine two factors: output and mechanism.

• Output is where the synthesized speech plays to and decides who hears the TTS message. Each destination uses one of the following outputs:

  • Local Playback - messages injected here play back locally on the user’s default render device (for example, loudspeakers or headphones).
  • Remote Transmission - messages injected here are sent to remote participants in connected sessions according to transmission policies (the same sessions that basic voice transmits to).
  • Local and Remote - messages injected here are simultaneously injected to Local Playback and Remote Transmission.

• Mechanism is how new messages are handled when there is an ongoing message playing. Each destination uses one of the following injection mechanisms:

  • Simple - destinations using this mechanism mix together new messages and ongoing messages to play them concurrently.
  • Queue - destinations using this mechanism queue new messages in the order they are sent. When the ongoing message finishes playing, this mechanism auto-triggers the message that is next in line.
  • Replace - destinations using this mechanism cancel any ongoing message and then replaces it with the new message.

You can inject synthesized speech into the following destinations:

• Remote Transmission

  • Enum value: TTSDestination::RemoteTransmission
  • Output: Remote Transmission
  • Mechanism: Simple

• Local Playback

  • Enum value: TTSDestination::LocalPlayback
  • Output: Local Playback
  • Mechanism: Simple

• Remote Transmission with Local Playback

  • Enum value: TTSDestination::RemoteTransmissionWithLocalPlayback
  • Output: Local and Remote
  • Mechanism: Simple

• Queued Remote Transmission

  • Enum value: TTSDestination::QueuedRemoteTransmission
  • Output: Remote Transmission
  • Mechanism: Queue
  • Caveat: Shares queue with Queued Remote Transmission with Local Playback.

• Queued Local Playback

  • Enum value: TTSDestination::QueuedLocalPlayback
  • Output: Local Playback
  • Mechanism: Queue

• Queued Remote Transmission with Local Playback

  • Enum value: TTSDestination::QueuedRemoteTransmissionWithLocalPlayback
  • Output: Local and Remote
  • Mechanism: Queue
  • Caveat: Shares queue with Queued Remote Transmission

• Screen Reader

  • Enum value: TTSDestination::ScreenReader
  • Output: Local Playback
  • Mechanism: Replace

You can obtain the state and content of all messages that are playing or are enqueued in any destination by using ITextToSpeech::GetMessages(TTSDestination Destination). Queued destinations return their TArray<ITTSMessage\*> in queue order, and others in the order that speech was injected.