Merge pull request #135 from jambonz/feat/gemini_tts

support gemini tts

lib/synth-audio.js

@@ -204,7 +204,10 @@ async function synthAudio(client, createHash, retrieveHash, logger, stats, { acc
     const startAt = process.hrtime();
     switch (vendor) {
       case 'google':
-        audioData = await synthGoogle(logger, {credentials, stats, language, voice, gender, key, text});
+        audioData = await synthGoogle(logger, {
+          credentials, stats, language, voice, gender, key, text, model, options, instructions,
+          renderForCaching, disableTtsStreaming, disableTtsCache
+        });
         break;
       case 'aws':
       case 'polly':
@@ -409,72 +412,124 @@ const synthPolly = async(createHash, retrieveHash, logger,
   }
 };
 
-const synthGoogle = async(logger, {credentials, stats, language, voice, gender, text}) => {
-  const client = new ttsGoogle.TextToSpeechClient(credentials);
-  // If google custom voice cloning is used.
-  // At this time 31 Oct 2024, google node sdk has not support voice cloning yet.
-  if (typeof voice === 'object' && voice.voice_cloning_key) {
-    try {
-      const accessToken = await client.auth.getAccessToken();
-      const projectId = await client.getProjectId();
 
-      const post = bent('https://texttospeech.googleapis.com', 'POST', 'json', {
+const synthGoogle = async(logger, {
-        'Authorization': `Bearer ${accessToken}`,
+  credentials, stats, language, voice, gender, key, text, model, options, instructions,
-        'x-goog-user-project': projectId,
+  renderForCaching, disableTtsStreaming, disableTtsCache
-        'Content-Type': 'application/json; charset=utf-8'
+}) => {
-      });
+  const isGemini = !!model;
+  const isVoiceCloning = typeof voice === 'object' && voice.voice_cloning_key;
+  // HD voices have pattern like en-US-Chirp3-HD-Charon
+  const isHDVoice = typeof voice === 'string' && voice.includes('-HD-');
 
-      const payload = {
+  // Streaming support for Google TTS (Gemini, HD voices, and standard voices)
-        input: {
+  // Voice cloning does not support streaming
-          text
+  if (!isVoiceCloning && !JAMBONES_DISABLE_TTS_STREAMING && !renderForCaching && !disableTtsStreaming) {
-        },
+    // Strip SSML tags for Gemini TTS (it doesn't support SSML)
-        voice: {
+    let inputText = text;
-          language_code: language,
+    if (isGemini && text.startsWith('<speak>')) {
-          voice_clone: {
+      inputText = text.replace(/<[^>]*>/g, '').trim();
-            voice_cloning_key: voice.voice_cloning_key
+      logger.info('synthGoogle: Gemini TTS does not support SSML, stripped tags from input');
-          }
-        },
-        audioConfig: {
-          // Cloning voice at this time still in v1 beta version, and it support LINEAR16 in Wav format, 24.000Hz
-          audioEncoding: 'LINEAR16',
-          sample_rate_hertz: 24000
-        }
-      };
-
-      const wav = await post('/v1beta1/text:synthesize', payload);
-      return {
-        audioContent: Buffer.from(wav.audioContent, 'base64'),
-        extension: 'wav',
-        sampleRate: 24000
-      };
-    } catch (err) {
-      logger.info({err: await err.text()}, 'synthGoogle returned error');
-      throw err;
     }
+
+    let params = '{';
+    params += `credentials=${Buffer.from(JSON.stringify(credentials.credentials)).toString('base64')}`;
+    params += `,playback_id=${key}`;
+    params += ',vendor=google';
+    params += `,voice=${voice}`;
+    params += `,language_code=${language || 'en-US'}`;
+    params += `,write_cache_file=${disableTtsCache ? 0 : 1}`;
+    const useLiveApi = options?.useLiveApi ?? isHDVoice;
+    const useGeminiTts = options?.useGeminiTts ?? isGemini;
+    params += `,use_live_api=${useLiveApi ? 1 : 0}`;
+    params += `,use_gemini_tts=${useGeminiTts ? 1 : 0}`;
+    if (model) params += `,model_name=${model}`;
+    if (gender) params += `,gender=${gender}`;
+    // comma is used to separate parameters in freeswitch tts module
+    const prompt = options?.prompt || instructions;
+    if (prompt) params += `,prompt=${prompt.replace(/\n/g, ' ').replace(/,/g, ';')}`;
+    params += '}';
+
+    return {
+      filePath: `say:${params}${(isGemini ? inputText : text).replace(/\n/g, ' ')}`,
+      servedFromCache: false,
+      rtt: 0
+    };
   }
 
-  const opts = {
+  const client = new ttsGoogle.TextToSpeechClient(credentials);
-    voice: {
+
-      ...(typeof voice === 'string' && {name: voice}),
+  // Build input based on voice type
-      ...(typeof voice === 'object' && {customVoice: voice}),
+  let input;
+  if (isGemini) {
+    // Gemini TTS does not support SSML - strip tags if present
+    let inputText = text;
+    if (text.startsWith('<speak>')) {
+      inputText = text.replace(/<[^>]*>/g, '').trim();
+      logger.info('synthGoogle: Gemini TTS does not support SSML, stripped tags from input');
+    }
+    // Use instructions as prompt for Gemini TTS style control, options.prompt can override
+    const prompt = options?.prompt || instructions;
+    input = {
+      text: inputText,
+      ...(prompt && { prompt })
+    };
+  } else {
+    input = text.startsWith('<speak>') ? { ssml: text } : { text };
+  }
+
+  // Build voice selection params based on voice type
+  let voiceParams;
+  if (isGemini) {
+    voiceParams = {
+      languageCode: language || 'en-US',
+      name: voice,
+      modelName: model
+    };
+  } else if (isVoiceCloning) {
+    voiceParams = {
+      languageCode: language,
+      voiceClone: {
+        voiceCloningKey: voice.voice_cloning_key
+      }
+    };
+  } else {
+    voiceParams = {
+      ...(typeof voice === 'string' && { name: voice }),
+      ...(typeof voice === 'object' && { customVoice: voice }),
       languageCode: language,
       ssmlGender: gender || 'SSML_VOICE_GENDER_UNSPECIFIED'
-    },
+    };
-    audioConfig: {audioEncoding: 'MP3'}
+  }
-  };
+
-  Object.assign(opts, {input: text.startsWith('<speak>') ? {ssml: text} : {text}});
+  // Build audio config based on voice type
+  let audioConfig;
+  let extension;
+  let sampleRate;
+  if (isVoiceCloning) {
+    audioConfig = { audioEncoding: 'LINEAR16', sampleRateHertz: 24000 };
+    extension = 'wav';
+    sampleRate = 24000;
+  } else {
+    audioConfig = { audioEncoding: 'MP3' };
+    extension = 'mp3';
+    sampleRate = 8000;
+  }
+
+  const opts = { input, voice: voiceParams, audioConfig };
+
   try {
-    const responses = await client.synthesizeSpeech(opts);
+    logger.debug({ opts }, 'synthGoogle: request');
+    const [response] = await client.synthesizeSpeech(opts);
     stats.increment('tts.count', ['vendor:google', 'accepted:yes']);
     client.close();
     return {
-      audioContent: responses[0].audioContent,
+      audioContent: response.audioContent,
-      extension: 'mp3',
+      extension,
-      sampleRate: 8000
+      sampleRate
     };
   } catch (err) {
-    console.error(err);
+    logger.info({ err, opts }, 'synthAudio: Error synthesizing speech using google');
-    logger.info({err, opts}, 'synthAudio: Error synthesizing speech using google');
     stats.increment('tts.count', ['vendor:google', 'accepted:no']);
     client && client.close();
     throw err;

package.json

@@ -30,7 +30,7 @@
     "@aws-sdk/client-polly": "^3.496.0",
     "@aws-sdk/client-sts": "^3.496.0",
     "@cartesia/cartesia-js": "^2.2.7",
-    "@google-cloud/text-to-speech": "^5.5.0",
+    "@google-cloud/text-to-speech": "^6.4.0",
     "@grpc/grpc-js": "^1.9.14",
     "@jambonz/realtimedb-helpers": "^0.8.7",
     "bent": "^7.3.12",

test/synth.js

@@ -41,6 +41,7 @@ test('Google speech synth tests', async(t) => {
       gender: 'FEMALE',
       text: 'This is a test.  This is only a test',
       salt: 'foo.bar',
+      renderForCaching: true,
     });
     t.ok(!opts.servedFromCache, `successfully synthesized google audio to ${opts.filePath}`);
 
@@ -55,6 +56,7 @@ test('Google speech synth tests', async(t) => {
       language: 'en-GB',
       gender: 'FEMALE',
       text: 'This is a test.  This is only a test',
+      renderForCaching: true,
     });
     t.ok(opts.servedFromCache, `successfully retrieved cached google audio from ${opts.filePath}`);
 
@@ -78,6 +80,7 @@ test('Google speech synth tests', async(t) => {
       language: 'en-GB',
       gender: 'FEMALE',
       text: 'This is a test.  This is only a test',
+      renderForCaching: true,
     });
     t.ok(!opts.servedFromCache, `successfully synthesized google audio regardless of current cache to ${opts.filePath}`);
   } catch (err) {
@@ -114,7 +117,8 @@ GCP_CUSTOM_VOICE_FILE nor GCP_CUSTOM_VOICE_JSON_KEY provided, GCP_CUSTOM_VOICE_M
       voice: {
         reportedUsage: 'REALTIME',
         model: process.env.GCP_CUSTOM_VOICE_MODEL
-      }
+      },
+      renderForCaching: true,
     });
     t.ok(!opts.servedFromCache, `successfully synthesized google custom voice audio to ${opts.filePath}`);
   } catch (err) {
@@ -132,7 +136,7 @@ test('Google speech voice cloning synth tests', async(t) => {
     !process.env.GCP_CUSTOM_VOICE_JSON_KEY ||
     !process.env.GCP_VOICE_CLONING_FILE &&
     !process.env.GCP_VOICE_CLONING_JSON_KEY) {
-    t.pass(`skipping google speech synth tests since neither 
+    t.pass(`skipping google speech synth tests since neither
 GCP_CUSTOM_VOICE_FILE nor GCP_CUSTOM_VOICE_JSON_KEY provided,
 GCP_VOICE_CLONING_FILE nor GCP_VOICE_CLONING_JSON_KEY is not provided`);
     return t.end();
@@ -156,7 +160,8 @@ GCP_VOICE_CLONING_FILE nor GCP_VOICE_CLONING_JSON_KEY is not provided`);
       text: 'This is a test. This is only a test. This is a test. This is only a test. This is a test. This is only a test',
       voice: {
         voice_cloning_key
-      }
+      },
+      renderForCaching: true,
     });
     t.ok(!opts.servedFromCache, `successfully synthesized google voice cloning audio to ${opts.filePath}`);
   } catch (err) {
@@ -166,6 +171,380 @@ GCP_VOICE_CLONING_FILE nor GCP_VOICE_CLONING_JSON_KEY is not provided`);
   client.quit();
 });
 
+test('Google Gemini TTS synth tests', async(t) => {
+  const fn = require('..');
+  const {synthAudio, client} = fn(opts, logger);
+
+  if (!process.env.GCP_FILE && !process.env.GCP_JSON_KEY) {
+    t.pass('skipping Google Gemini TTS synth tests since neither GCP_FILE nor GCP_JSON_KEY provided');
+    return t.end();
+  }
+  try {
+    const str = process.env.GCP_JSON_KEY || fs.readFileSync(process.env.GCP_FILE);
+    const creds = JSON.parse(str);
+    const geminiModel = process.env.GCP_GEMINI_TTS_MODEL || 'gemini-2.5-flash-tts';
+
+    // Test Gemini TTS with model and instructions (both required for Gemini)
+    let result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'Kore',
+      model: geminiModel,
+      text: 'Hello, this is a test of Google Gemini text to speech.',
+      instructions: 'Speak clearly and naturally.',
+      renderForCaching: true,
+    });
+    t.ok(!result.servedFromCache, `successfully synthesized Google Gemini TTS audio to ${result.filePath}`);
+    t.ok(result.filePath.endsWith('.mp3'), 'Gemini TTS audio file has correct extension');
+
+    // Test Gemini TTS with different voice and instructions
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'Charon',
+      model: geminiModel,
+      text: 'Welcome to our service. How can I help you today?',
+      instructions: 'Speak in a warm, friendly and professional tone.',
+      renderForCaching: true,
+    });
+    t.ok(!result.servedFromCache, `successfully synthesized Gemini TTS with instructions to ${result.filePath}`);
+
+    // Test cache retrieval
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'Kore',
+      model: geminiModel,
+      text: 'Hello, this is a test of Google Gemini text to speech.',
+      instructions: 'Speak clearly and naturally.',
+      renderForCaching: true,
+    });
+    t.ok(result.servedFromCache, `successfully retrieved Gemini TTS audio from cache ${result.filePath}`);
+
+    // Test SSML stripping (Gemini doesn't support SSML)
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'Leda',
+      model: geminiModel,
+      text: '<speak>This SSML should be stripped for Gemini TTS.</speak>',
+      instructions: 'Speak naturally.',
+      disableTtsCache: true,
+      renderForCaching: true,
+    });
+    t.ok(!result.servedFromCache, `successfully synthesized Gemini TTS with SSML stripped to ${result.filePath}`);
+
+  } catch (err) {
+    console.error(err);
+    t.end(err);
+  }
+  client.quit();
+});
+
+test('Google TTS streaming tests (!JAMBONES_DISABLE_TTS_STREAMING)', async(t) => {
+  // Ensure streaming is enabled (default behavior)
+  delete process.env.JAMBONES_DISABLE_TTS_STREAMING;
+
+  // Clear require cache to reload config with new env var
+  delete require.cache[require.resolve('../lib/config')];
+  delete require.cache[require.resolve('../lib/synth-audio')];
+  delete require.cache[require.resolve('..')];
+
+  const fn = require('..');
+  const {synthAudio, client} = fn(opts, logger);
+
+  if (!process.env.GCP_FILE && !process.env.GCP_JSON_KEY) {
+    t.pass('skipping Google TTS streaming tests since neither GCP_FILE nor GCP_JSON_KEY provided');
+    return t.end();
+  }
+
+  try {
+    const str = process.env.GCP_JSON_KEY || fs.readFileSync(process.env.GCP_FILE);
+    const creds = JSON.parse(str);
+    const geminiModel = process.env.GCP_GEMINI_TTS_MODEL || 'gemini-2.5-flash-tts';
+
+    // Test 1: Standard voice streaming (use_live_api=0)
+    let result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'en-US-Wavenet-D',
+      gender: 'MALE',
+      text: 'This is a test of standard voice streaming.',
+      disableTtsCache: true
+    });
+    t.ok(result.filePath.startsWith('say:'), 'Standard voice returns streaming say: path');
+    t.ok(result.filePath.includes('vendor=google'), 'Standard voice streaming path contains vendor=google');
+    t.ok(result.filePath.includes('use_live_api=0'), 'Standard voice uses use_live_api=0');
+    t.ok(result.filePath.includes('use_gemini_tts=0'), 'Standard voice uses use_gemini_tts=0');
+    t.ok(result.filePath.includes('voice=en-US-Wavenet-D'), 'Standard voice streaming path contains voice');
+    // Verify credentials are base64 encoded (no raw JSON braces that would break FreeSWitch parsing)
+    t.ok(result.filePath.includes('credentials='), 'Standard voice streaming path contains credentials');
+    t.ok(!result.filePath.includes('credentials={'), 'Credentials are not raw JSON (base64 encoded)');
+
+    // Test 2: HD voice streaming (use_live_api=1)
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'en-US-Chirp3-HD-Charon',
+      text: 'This is a test of HD voice streaming.',
+      disableTtsCache: true
+    });
+    t.ok(result.filePath.startsWith('say:'), 'HD voice returns streaming say: path');
+    t.ok(result.filePath.includes('vendor=google'), 'HD voice streaming path contains vendor=google');
+    t.ok(result.filePath.includes('use_live_api=1'), 'HD voice uses use_live_api=1 (Live API)');
+    t.ok(result.filePath.includes('use_gemini_tts=0'), 'HD voice uses use_gemini_tts=0');
+    t.ok(result.filePath.includes('voice=en-US-Chirp3-HD-Charon'), 'HD voice streaming path contains voice');
+
+    // Test 3: Gemini TTS streaming (use_live_api=1)
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'Kore',
+      model: geminiModel,
+      text: 'This is a test of Gemini TTS streaming.',
+      instructions: 'Speak naturally.',
+      disableTtsCache: true
+    });
+    t.ok(result.filePath.startsWith('say:'), 'Gemini TTS returns streaming say: path');
+    t.ok(result.filePath.includes('vendor=google'), 'Gemini TTS streaming path contains vendor=google');
+    t.ok(result.filePath.includes('use_live_api=0'), 'Gemini TTS uses use_live_api=0');
+    t.ok(result.filePath.includes('use_gemini_tts=1'), 'Gemini TTS uses use_gemini_tts=1');
+    t.ok(result.filePath.includes(`model_name=${geminiModel}`), 'Gemini TTS streaming path contains model_name');
+    t.ok(result.filePath.includes('prompt=Speak naturally.'), 'Gemini TTS streaming path contains prompt');
+
+    // Test 4: Gemini TTS with SSML stripping in streaming mode
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'Leda',
+      model: geminiModel,
+      text: '<speak>This SSML should be stripped.</speak>',
+      instructions: 'Speak naturally.',
+      disableTtsCache: true
+    });
+    t.ok(result.filePath.startsWith('say:'), 'Gemini TTS with SSML returns streaming say: path');
+    t.ok(!result.filePath.includes('<speak>'), 'SSML tags are stripped from streaming path');
+    t.ok(result.filePath.includes('This SSML should be stripped.'), 'Text content is preserved after SSML stripping');
+
+    // Test 5: Gemini TTS with prompt containing special characters
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'Kore',
+      model: geminiModel,
+      text: 'Testing special characters in prompt.',
+      options: { prompt: 'Speak in a warm, friendly tone' },
+      disableTtsCache: true
+    });
+    t.ok(result.filePath.startsWith('say:'), 'Gemini TTS with special chars returns streaming say: path');
+    // Commas in prompt should be replaced with semicolons
+    t.ok(result.filePath.includes('prompt=Speak in a warm; friendly tone'), 'Commas in prompt are escaped to semicolons');
+
+    // Test 6: options.useLiveApi override (force live api on standard voice)
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'en-US-Wavenet-D',
+      text: 'Testing useLiveApi option override.',
+      options: { useLiveApi: true },
+      disableTtsCache: true
+    });
+    t.ok(result.filePath.includes('use_live_api=1'), 'options.useLiveApi=true overrides default for standard voice');
+    t.ok(result.filePath.includes('use_gemini_tts=0'), 'use_gemini_tts remains 0 for standard voice');
+
+    // Test 7: options.useGeminiTts override (force gemini tts without model)
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'Kore',
+      text: 'Testing useGeminiTts option override.',
+      options: { useGeminiTts: true },
+      disableTtsCache: true
+    });
+    t.ok(result.filePath.includes('use_gemini_tts=1'), 'options.useGeminiTts=true overrides default');
+    t.ok(result.filePath.includes('use_live_api=0'), 'use_live_api remains 0 without HD voice');
+
+    // Test 8: Both options override together
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'en-US-Wavenet-D',
+      text: 'Testing both options override.',
+      options: { useLiveApi: true, useGeminiTts: true },
+      disableTtsCache: true
+    });
+    t.ok(result.filePath.includes('use_live_api=1'), 'options.useLiveApi=true works with useGeminiTts');
+    t.ok(result.filePath.includes('use_gemini_tts=1'), 'options.useGeminiTts=true works with useLiveApi');
+
+  } catch (err) {
+    console.error(err);
+    t.end(err);
+  }
+  client.quit();
+});
+
+test('Google TTS non-streaming tests (JAMBONES_DISABLE_TTS_STREAMING=true)', async(t) => {
+  // Enable streaming disable flag
+  process.env.JAMBONES_DISABLE_TTS_STREAMING = 'true';
+
+  // Clear require cache to reload config with new env var
+  delete require.cache[require.resolve('../lib/config')];
+  delete require.cache[require.resolve('../lib/synth-audio')];
+  delete require.cache[require.resolve('..')];
+
+  const fn = require('..');
+  const {synthAudio, client} = fn(opts, logger);
+
+  if (!process.env.GCP_FILE && !process.env.GCP_JSON_KEY) {
+    t.pass('skipping Google TTS non-streaming tests since neither GCP_FILE nor GCP_JSON_KEY provided');
+    delete process.env.JAMBONES_DISABLE_TTS_STREAMING;
+    return t.end();
+  }
+
+  try {
+    const str = process.env.GCP_JSON_KEY || fs.readFileSync(process.env.GCP_FILE);
+    const creds = JSON.parse(str);
+    const geminiModel = process.env.GCP_GEMINI_TTS_MODEL || 'gemini-2.5-flash-tts';
+
+    // Test 1: Standard voice falls back to non-streaming API
+    let result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'en-US-Wavenet-D',
+      gender: 'MALE',
+      text: 'This is a test with streaming disabled.',
+      disableTtsCache: true
+    });
+    t.ok(!result.filePath.startsWith('say:'), 'Standard voice does NOT return streaming say: path when disabled');
+    t.ok(result.filePath.endsWith('.mp3'), 'Standard voice returns mp3 file path');
+
+    // Test 2: HD voice falls back to non-streaming API
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'en-US-Chirp3-HD-Charon',
+      text: 'This is a test of HD voice with streaming disabled.',
+      disableTtsCache: true
+    });
+    t.ok(!result.filePath.startsWith('say:'), 'HD voice does NOT return streaming say: path when disabled');
+    t.ok(result.filePath.endsWith('.mp3'), 'HD voice returns mp3 file path');
+
+    // Test 3: Gemini TTS falls back to non-streaming API
+    result = await synthAudio(stats, {
+      vendor: 'google',
+      credentials: {
+        credentials: {
+          client_email: creds.client_email,
+          private_key: creds.private_key,
+        },
+      },
+      language: 'en-US',
+      voice: 'Kore',
+      model: geminiModel,
+      text: 'This is a test of Gemini TTS with streaming disabled.',
+      instructions: 'Speak naturally.',
+      disableTtsCache: true
+    });
+    t.ok(!result.filePath.startsWith('say:'), 'Gemini TTS does NOT return streaming say: path when disabled');
+    t.ok(result.filePath.endsWith('.mp3'), 'Gemini TTS returns mp3 file path');
+
+  } catch (err) {
+    console.error(err);
+    t.end(err);
+  } finally {
+    // Clean up: restore default behavior
+    delete process.env.JAMBONES_DISABLE_TTS_STREAMING;
+    delete require.cache[require.resolve('../lib/config')];
+    delete require.cache[require.resolve('../lib/synth-audio')];
+    delete require.cache[require.resolve('..')];
+  }
+  client.quit();
+});
+
 test('AWS speech synth tests', async(t) => {
   const fn = require('..');
   const {synthAudio, client} = fn(opts, logger);