Example: Half-cascade with ElevenLabs

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/**
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 * Voximplant + OpenAI Realtime API + ElevenLabs TTS demo
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 * Scenario: OpenAI handles STT/LLM, ElevenLabs handles TTS (half-cascade).
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 */
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require(Modules.OpenAI);
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require(Modules.ElevenLabs);
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const OPENAI_MODEL = "gpt-realtime-2.1";
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const SYSTEM_PROMPT = `
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You are Voxi, a helpful phone assistant.
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Keep responses short and telephony-friendly.
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Always reply in English.
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`;
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const ELEVENLABS_VOICE_ID = "21m00Tcm4TlvDq8ikWAM";
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const ELEVENLABS_MODEL_ID = "eleven_turbo_v2_5";
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const SESSION_CONFIG = {
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    session: {
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        type: "realtime",
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        model: OPENAI_MODEL,
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        instructions: SYSTEM_PROMPT,
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        output_modalities: ["text"],
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        audio: {
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            input: {
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                turn_detection: {type: "server_vad", interrupt_response: true},
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            },
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        },
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    },
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};
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VoxEngine.addEventListener(AppEvents.CallAlerting, async ({call}) => {
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    let voiceAIClient;
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    let ttsPlayer;
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    call.addEventListener(CallEvents.Disconnected, () => VoxEngine.terminate());
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    call.addEventListener(CallEvents.Failed, () => VoxEngine.terminate());
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    try {
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        call.answer();
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        // call.record({hd_audio: true, stereo: true}); // Optional: record the call
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        const openAiKey = VoxEngine.getSecretValue("OPENAI_API_KEY");
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        voiceAIClient = await OpenAI.createRealtimeAPIClient({
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            apiKey: openAiKey,
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            model: OPENAI_MODEL,
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            onWebSocketClose: (event) => {
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                Logger.write("===OpenAI.WebSocket.Close===");
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                if (event) Logger.write(JSON.stringify(event));
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                VoxEngine.terminate();
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            },
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        });
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        voiceAIClient.addEventListener(OpenAI.RealtimeAPIEvents.SessionCreated, () => {
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            voiceAIClient.sessionUpdate(SESSION_CONFIG);
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        });
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        voiceAIClient.addEventListener(OpenAI.RealtimeAPIEvents.SessionUpdated, () => {
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            call.sendMediaTo(voiceAIClient);  // bridge media between the call and OpenAI
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            // create the TTS player and pass the config parameters
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            ttsPlayer = ElevenLabs.createRealtimeTTSPlayer(" ", {
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                // headers: [{name: "xi-api-key", value: VoxEngine.getSecretValue('ELEVENLABS_API_KEY')}], // optional
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                pathParameters: {voice_id: ELEVENLABS_VOICE_ID},
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                queryParameters: {
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                    model_id: ELEVENLABS_MODEL_ID,
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                },
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            });
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            ttsPlayer.sendMediaTo(call); // bridge media between the TTS player and the call
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            voiceAIClient.responseCreate({instructions: "Hello! How can I help today?"});
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        });
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        voiceAIClient.addEventListener(OpenAI.RealtimeAPIEvents.ResponseOutputTextDone, (event) => {
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            const payload = event?.data?.payload || event?.data || {};
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            const text = payload.text || payload.delta;
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            if (!text || !ttsPlayer) return;
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            Logger.write(`===AGENT_TEXT=== ${text}`);
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            ttsPlayer.append(text, true);
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        });
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        // Barge-in: clear both OpenAI and ElevenLabs buffers
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        voiceAIClient.addEventListener(OpenAI.RealtimeAPIEvents.InputAudioBufferSpeechStarted, () => {
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            Logger.write("===BARGE-IN: OpenAI.InputAudioBufferSpeechStarted===");
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            voiceAIClient.clearMediaBuffer();
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            ttsPlayer?.clearBuffer();
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        });
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        // ---------------------- Log all other events for debugging -----------------------
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        [
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            OpenAI.RealtimeAPIEvents.ResponseCreated,
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            OpenAI.RealtimeAPIEvents.ResponseDone,
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            OpenAI.RealtimeAPIEvents.ResponseOutputTextDelta,
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            OpenAI.RealtimeAPIEvents.ConnectorInformation,
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            OpenAI.RealtimeAPIEvents.HTTPResponse,
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            OpenAI.RealtimeAPIEvents.WebSocketError,
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            OpenAI.RealtimeAPIEvents.Unknown,
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            OpenAI.Events.WebSocketMediaStarted,
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            OpenAI.Events.WebSocketMediaEnded,
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        ].forEach((eventName) => {
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            voiceAIClient.addEventListener(eventName, (event) => {
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                Logger.write(`===${event.name}===`);
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                if (event?.data) Logger.write(JSON.stringify(event.data));
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            });
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        });
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    } catch (error) {
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        Logger.write("===UNHANDLED_ERROR===");
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        Logger.write(error);
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        voiceAIClient?.close();
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        VoxEngine.terminate();
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    }
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});