What is the Spring AI AudioModel and how does it support speech synthesis?

Spring AI includes an AudioModel (specifically SpeechModel) abstraction for text-to-speech (TTS) generation. This covers converting text responses to spoken audio — useful for voice assistants, accessibility features, and audio content pipelines. Currently, the primary provider with TTS support in Spring AI is OpenAI, which offers the tts-1 and tts-1-hd models with multiple voices (alloy, echo, fable, onyx, nova, shimmer).

@Service
public class SpeechService {
    private final SpeechModel speechModel;

    public SpeechService(SpeechModel speechModel) {
        this.speechModel = speechModel;
    }

    public byte[] synthesise(String text) {
        SpeechResponse response = speechModel.call(
            new SpeechPrompt(text,
                OpenAiAudioSpeechOptions.builder()
                    .withVoice(OpenAiAudioApi.SpeechRequest.Voice.NOVA)
                    .withResponseFormat(OpenAiAudioApi.SpeechRequest.AudioResponseFormat.MP3)
                    .withSpeed(1.0f)
                    .build())
        );
        return response.getResult().getOutput();  // returns byte[] audio data
    }
}

The SpeechResponse carries the audio as a byte[] which you can write to a file, stream as an HTTP response, or forward to a message broker. The response format can be MP3, OPUS, AAC, FLAC, or WAV depending on the provider's supported formats.

Speech-to-text (transcription) is a separate capability covered by the AudioTranscriptionModel abstraction, also backed by OpenAI Whisper in Spring AI's current implementation.

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