Engines and sessions

The examples use two kinds of object: a loaded engine and a session for one recording or utterance. Keeping them separate lets you load a model once and reuse it for later requests.

Libraries

aria-stt provides transcription, aria-tts provides synthesis, and aria-kit provides microphone capture, audio playback, and shared speech types.

The engine crates re-export their common types in prelude. That is why transcription imports Transcription, RecordingReader, and Microphone from aria_stt, and synthesis imports Synthesis and CancelToken from aria_tts. Add aria-kit directly only for playback.

Transcription

Load Whisper once
  → construct Transcription
  → provide a WAV or microphone recording
  → receive finalized text

Whisper loads and runs the recognition model. Transcription chooses how to process the recording and applies any text layers. Session manages transcription of one recording.

For a completed file, transcribe_file returns one Transcript. For live input, Session::next_finalized returns segments as they become final, and stop returns the complete transcript. Finalized segments stay unchanged.

The libraries do not insert text into another application. Your code decides whether to display, save, or deliver it.

Synthesis

Load Kokoro once
  → construct Synthesis
  → start an utterance
  → read audio samples until completion

Kokoro supplies the model and voices. Synthesis starts one worker per utterance. Its session gives you the sample rate and generated audio samples. Dropping the session requests cancellation and waits for the thread to stop.

The system voice has a different output: it speaks through the platform’s voice program and provides no audio samples.

Blocking calls

Model loading, transcription, audio reads, and speaking are synchronous calls. Run them on a worker thread when integrating with a UI or an asynchronous application. Streaming can produce output before an operation finishes, but reading the next result can still block.