support stt latency metrics (#1252)

* support stt latency metrics

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* enable stt latency calculator by config verb

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* fix jslint

* fixed gather timeout does not have latency calculation

* upadte verb specification to use notifySttLatency

* move stt latency metric from call session to stt-latency calculator

* wip

lib/config.js

@@ -231,5 +231,5 @@ module.exports = {
   JAMBONES_DIAL_SBC_FOR_REGISTERED_USER,
   JAMBONES_MEDIA_TIMEOUT_MS,
   JAMBONES_MEDIA_HOLD_TIMEOUT_MS,
-  JAMBONES_TRANSCRIBE_EP_DESTROY_DELAY_MS
+  JAMBONES_TRANSCRIBE_EP_DESTROY_DELAY_MS,
 };

lib/session/call-session.js

@@ -38,6 +38,7 @@ const BADPRECONDITIONS = 'preconditions not met';
 const CALLER_CANCELLED_ERR_MSG = 'Response not sent due to unknown transaction';
 const { NonFatalTaskError} = require('../utils/error');
 const { createMediaEndpoint } = require('../utils/media-endpoint');
+const SttLatencyCalculator = require('../utils/stt-latency-calculator');
 const sqlRetrieveQueueEventHook = `SELECT * FROM webhooks 
 WHERE webhook_sid = 
 (
@@ -147,6 +148,30 @@ class CallSession extends Emitter {
     this.conversationTurns = [];
     this.on('userSaid', this._onUserSaid.bind(this));
     this.on('botSaid', this._onBotSaid.bind(this));
+    /**
+     * Support STT latency
+     */
+    this.sttLatencyCalculator = new SttLatencyCalculator({
+      logger,
+      cs: this
+    });
+    this.on('transcribe-start', () => {
+      this.sttLatencyCalculator.resetTime();
+    });
+    this.on('on-transcription', () => {
+      this.sttLatencyCalculator.onTranscriptionReceived();
+    });
+    this.on('transcribe-stop', () => {
+      this.sttLatencyCalculator.onTranscribeStop();
+    });
+  }
+
+  get notifySttLatencyEnabled() {
+    return this._notifySttLatencyEnabled || false;
+  }
+
+  set notifySttLatencyEnabled(enabled) {
+    this._notifySttLatencyEnabled = enabled;
   }
 
   /**
@@ -2480,6 +2505,8 @@ Duration=${duration} `
     this.clearOrRestoreActionHookDelayProcessor().catch((err) => {});
 
     this.ttsStreamingBuffer?.stop();
+
+    this.sttLatencyCalculator?.stop();
   }
 
   /**
@@ -3127,6 +3154,20 @@ Duration=${duration} `
       return `assistant: ${t.text}`;
     }).join('\n');
   }
+
+  startSttLatencyVad() {
+    if (this.notifySttLatencyEnabled) {
+      this.sttLatencyCalculator.start();
+    }
+  }
+
+  stopSttLatencyVad() {
+    this.sttLatencyCalculator.stop();
+  }
+
+  calculateSttLatency() {
+    return this.sttLatencyCalculator.calculateLatency();
+  }
 }
 
 module.exports = CallSession;

lib/tasks/config.js

@@ -24,6 +24,9 @@ class TaskConfig extends Task {
     if ('notifyEvents' in this.data) {
       this.notifyEvents = !!this.data.notifyEvents;
     }
+    if (this.hasNotifySttLatency) {
+      this.notifySttLatency = !!this.data.notifySttLatency;
+    }
 
     if (this.bargeIn.enable) {
       this.gatherOpts = {
@@ -83,6 +86,7 @@ class TaskConfig extends Task {
   get hasVad() { return Object.keys(this.vad).length; }
   get hasFillerNoise() { return Object.keys(this.fillerNoise).length; }
   get hasReferHook() { return Object.keys(this.data).includes('referHook'); }
+  get hasNotifySttLatency() { return Object.keys(this.data).includes('notifySttLatency'); }
   get hasTtsStream() { return Object.keys(this.ttsStream).length; }
 
   get summary() {
@@ -112,6 +116,8 @@ class TaskConfig extends Task {
     if (this.hasFillerNoise) phrase.push(`fillerNoise ${this.fillerNoise.enable ? 'on' : 'off'}`);
     if (this.data.amd) phrase.push('enable amd');
     if (this.notifyEvents) phrase.push(`event notification ${this.notifyEvents ? 'on' : 'off'}`);
+    if (this.hasNotifySttLatency) phrase.push(
+      `notifySttLatency ${this.notifySttLatency ? 'on' : 'off'}`);
     if (this.onHoldMusic) phrase.push(`onHoldMusic: ${this.onHoldMusic}`);
     if ('boostAudioSignal' in this.data) phrase.push(`setGain ${this.data.boostAudioSignal}`);
     if (this.hasReferHook) phrase.push('set referHook');
@@ -130,6 +136,11 @@ class TaskConfig extends Task {
       cs.notifyEvents = !!this.data.notifyEvents;
     }
 
+    if (this.hasNotifySttLatency) {
+      this.logger.debug(`turning notifySttLatency ${this.notifySttLatency ? 'on' : 'off'}`);
+      cs.notifySttLatencyEnabled = this.notifySttLatency;
+    }
+
     if (this.onHoldMusic) {
       cs.onHoldMusic = this.onHoldMusic;
     }
@@ -318,7 +329,10 @@ class TaskConfig extends Task {
         voiceMs: this.vad.voiceMs || 250,
         silenceMs: this.vad.silenceMs || 150,
         strategy: this.vad.strategy || 'one-shot',
-        mode: (this.vad.mode !== undefined && this.vad.mode !== null) ? this.vad.mode : 2
+        mode: (this.vad.mode !== undefined && this.vad.mode !== null) ? this.vad.mode : 2,
+        vendor: this.vad.vendor || 'silero',
+        threshold: this.vad.threshold || 0.5,
+        speechPadMs: this.vad.speechPadMs || 30,
       };
     }
 

lib/tasks/gather.js

@@ -351,6 +351,7 @@ class TaskGather extends SttTask {
     this.sayTask?.span.end();
     this._stopVad();
     this._resolve('killed');
+    cs.stopSttLatencyVad();
   }
 
   updateTaskInProgress(opts) {
@@ -390,16 +391,7 @@ class TaskGather extends SttTask {
       if (this.digitBuffer.length === 0 && this.needsStt) {
         // DTMF is higher priority than STT.
         this.removeCustomEventListeners();
-        // Fix for https://github.com/jambonz/jambonz-feature-server/issues/1281
+        this._stopTranscribing(ep);
-        // We should immediately call stop transcription from gather
-        // so that next gather can start transcription immediately
-        ep.stopTranscription({
-          vendor: this.vendor,
-          bugname: this.bugname,
-          gracefulShutdown: false
-        })
-          .catch((err) => this.logger.error({err},
-            ` Received DTMF, Error stopping transcription for vendor ${this.vendor}`));
       }
       this.digitBuffer += evt.dtmf;
       const len = this.digitBuffer.length;
@@ -686,6 +678,9 @@ class TaskGather extends SttTask {
         target_sid: this.cs.callSid
       });
     }).catch((err) => this.logger.info({err}, 'Error generating alert for tts failure'));
+
+    // Some vendor use single connection, that we cannot use onConnect event to track transcription start
+    this.cs.emit('transcribe-start');
   }
 
   _startTimer() {
@@ -869,6 +864,10 @@ class TaskGather extends SttTask {
     if (finished === 'true') return;
 
     if (this.vendor === 'ibm' && evt?.state === 'listening') return;
+
+    // emit an event to the call session to track the time transcription is received
+    cs.emit('on-transcription');
+
     if (this.vendor === 'deepgram' && evt.type === 'UtteranceEnd') {
       /* we will only get this when we have set utterance_end_ms */
       if (this._bufferedTranscripts.length === 0) {
@@ -952,6 +951,12 @@ class TaskGather extends SttTask {
         }
       }
 
+      // receive a final transcript, calculate the stt latency for this transcript
+      const sttLatency = this.cs.calculateSttLatency();
+      if (!emptyTranscript && sttLatency) {
+        this.stt_latency_ms += `${sttLatency.stt_latency_ms},`;
+      }
+
       if (this.isContinuousAsr) {
         /* append the transcript and start listening again for asrTimeout */
         const t = evt.alternatives[0].transcript;
@@ -1103,12 +1108,7 @@ class TaskGather extends SttTask {
 
   async _startFallback(cs, ep, evt) {
     if (this.canFallback) {
-      ep.stopTranscription({
+      this._stopTranscribing(ep);
-        vendor: this.vendor,
-        bugname: this.bugname,
-        gracefulShutdown: false
-      })
-        .catch((err) => this.logger.error({err}, `Error stopping transcription for primary vendor ${this.vendor}`));
       try {
         this.logger.debug('gather:_startFallback');
         this.notifyError({ msg: 'ASR error',
@@ -1237,21 +1237,26 @@ class TaskGather extends SttTask {
     }
   }
 
+  async _stopTranscribing(ep) {
+    // Fix for https://github.com/jambonz/jambonz-feature-server/issues/1281
+    // We should immediately call stop transcription from gather
+    // so that next gather can start transcription immediately
+    ep.stopTranscription({
+      vendor: this.vendor,
+      bugname: this.bugname,
+      gracefulShutdown: false
+    })
+      .catch((err) => {
+        if (this.resolved) return;
+        this.logger.error({err}, 'Error stopping transcription');
+      });
+    this.cs.emit('transcribe-stop');
+  }
+
   async _resolve(reason, evt) {
     this.logger.info({evt}, `TaskGather:resolve with reason ${reason}`);
     if (this.needsStt && this.ep && this.ep.connected) {
-      // Fix for https://github.com/jambonz/jambonz-feature-server/issues/1281
+      this._stopTranscribing(this.ep);
-      // We should immediately call stop transcription from gather
-      // so that next gather can start transcription immediately
-      this.ep.stopTranscription({
-        vendor: this.vendor,
-        bugname: this.bugname,
-        gracefulShutdown: false
-      })
-        .catch((err) => {
-          if (this.resolved) return;
-          this.logger.error({err}, 'Error stopping transcription');
-        });
     }
     if (this.resolved) {
       this.logger.debug('TaskGather:_resolve - already resolved');
@@ -1270,11 +1275,28 @@ class TaskGather extends SttTask {
     this._clearAsrTimer();
     this._clearFinalAsrTimer();
 
+    let sttLatencyMetrics = {};
+    if (this.needsStt) {
+      const sttLatency = this.cs.calculateSttLatency();
+      if (sttLatency) {
+        this.stt_latency_ms = this.stt_latency_ms.endsWith(',') ?
+          this.stt_latency_ms.slice(0, -1) : this.stt_latency_ms;
+        sttLatencyMetrics = {
+          'stt.latency_ms': this.stt_latency_ms,
+          'stt.talkspurts': JSON.stringify(sttLatency.talkspurts),
+          'stt.start_time': sttLatency.stt_start_time,
+          'stt.stop_time': sttLatency.stt_stop_time,
+          'stt.usage': sttLatency.stt_usage,
+        };
+      }
+    }
+
     this.span.setAttributes({
       channel: 1,
       'stt.label': this.label || 'None',
       'stt.resolve': reason,
-      'stt.result': JSON.stringify(evt)
+      'stt.result': JSON.stringify(evt),
+      ...sttLatencyMetrics
     });
 
     if (this.callSession && this.callSession.callGone) {
@@ -1302,6 +1324,9 @@ class TaskGather extends SttTask {
 
     let returnedVerbs = false;
     try {
+      const latencies = Object.fromEntries(
+        Object.entries(sttLatencyMetrics).map(([key, value]) => [key.replace('stt.', 'stt_'), value])
+      );
       if (reason.startsWith('dtmf')) {
         if (this.parentTask) this.parentTask.emit('dtmf', evt);
         else {
@@ -1315,7 +1340,7 @@ class TaskGather extends SttTask {
         else {
           this.emit('transcription', evt);
           this.logger.debug('TaskGather:_resolve - invoking performAction');
-          returnedVerbs = await this.performAction({speech: evt, reason: 'speechDetected'});
+          returnedVerbs = await this.performAction({speech: evt, reason: 'speechDetected', ...latencies});
           this.logger.debug({returnedVerbs}, 'TaskGather:_resolve - back from performAction');
         }
       }
@@ -1323,20 +1348,20 @@ class TaskGather extends SttTask {
         if (this.parentTask) this.parentTask.emit('timeout', evt);
         else {
           this.emit('timeout', evt);
-          returnedVerbs = await this.performAction({reason: 'timeout'});
+          returnedVerbs = await this.performAction({reason: 'timeout', ...latencies});
         }
       }
       else if (reason.startsWith('stt-error')) {
         if (this.parentTask) this.parentTask.emit('stt-error', evt);
         else {
           this.emit('stt-error', evt);
-          returnedVerbs = await this.performAction({reason: 'error', details: evt.error});
+          returnedVerbs = await this.performAction({reason: 'error', details: evt.error, ...latencies});
         }
       } else if (reason.startsWith('stt-low-confidence')) {
         if (this.parentTask) this.parentTask.emit('stt-low-confidence', evt);
         else {
           this.emit('stt-low-confidence', evt);
-          returnedVerbs = await this.performAction({speech:evt, reason: 'stt-low-confidence'});
+          returnedVerbs = await this.performAction({speech:evt, reason: 'stt-low-confidence', ...latencies});
         }
       }
     } catch (err) {  /*already logged error*/ }

lib/tasks/stt-task.js

@@ -4,6 +4,7 @@ const crypto = require('crypto');
 const { TaskPreconditions, CobaltTranscriptionEvents } = require('../utils/constants');
 const { SpeechCredentialError } = require('../utils/error');
 const {JAMBONES_AWS_TRANSCRIBE_USE_GRPC} = require('../config');
+const {TaskName} = require('../utils/constants.json');
 
 /**
  * "Please insert turns here: {{turns:4}}"
@@ -84,6 +85,9 @@ class SttTask extends Task {
     /*bug name prefix */
     this.bugname_prefix = '';
 
+    // stt latency calculator
+    this.stt_latency_ms = '';
+
   }
 
   async exec(cs, {ep, ep2}) {
@@ -91,6 +95,12 @@ class SttTask extends Task {
     this.ep = ep;
     this.ep2 = ep2;
 
+    // start vad from stt latency calculator
+    if (this.name !== TaskName.Gather ||
+      this.name === TaskName.Gather && this.needsStt) {
+      cs.startSttLatencyVad();
+    }
+
     // use session preferences if we don't have specific verb-level settings.
     if (cs.recognizer) {
       for (const k in cs.recognizer) {
@@ -400,7 +410,7 @@ class SttTask extends Task {
     dgOptions.utteranceEndMs = dgOptions.utteranceEndMs || asrTimeout;
   }
 
-  _onVendorConnect(_cs, _ep) {
+  _onVendorConnect(cs, _ep) {
     this.logger.debug(`TaskGather:_on${this.vendor}Connect`);
   }
 

lib/tasks/transcribe.js

@@ -152,12 +152,15 @@ class TaskTranscribe extends SttTask {
         .catch((err) => this.logger.info(err, 'Error TaskTranscribe:kill'));
     }
 
+    this.cs.emit('transcribe-stop');
+
     return stopTranscription;
   }
 
   async kill(cs) {
     super.kill(cs);
     const stopTranscription = this._stopTranscription();
+    cs.stopSttLatencyVad();
     // hangup after 1 sec if we don't get a final transcription
     if (stopTranscription) this._timer = setTimeout(() => this.notifyTaskDone(), 1500);
     else this.notifyTaskDone();
@@ -423,6 +426,9 @@ class TaskTranscribe extends SttTask {
       bugname: this.bugname,
       hostport: this.hostport
     });
+
+    // Some vendor use single connection, that we cannot use onConnect event to track transcription start
+    this.cs.emit('transcribe-start');
   }
 
   async _onTranscription(cs, ep, channel, evt, fsEvent) {
@@ -441,6 +447,9 @@ class TaskTranscribe extends SttTask {
 
     if (this.vendor === 'ibm' && evt?.state === 'listening') return;
 
+    // emit an event to the call session to track the time transcription is received
+    cs.emit('on-transcription');
+
     if (this.vendor === 'deepgram' && evt.type === 'UtteranceEnd') {
       /* we will only get this when we have set utterance_end_ms */
 
@@ -602,14 +611,28 @@ class TaskTranscribe extends SttTask {
   }
 
   async _resolve(channel, evt) {
+    let sttLatencyMetrics = {};
     if (evt.is_final) {
+      const sttLatency = this.cs.calculateSttLatency();
+      if (sttLatency) {
+        sttLatencyMetrics = {
+          'stt.latency_ms': `${sttLatency.stt_latency_ms}`,
+          'stt.talkspurts': JSON.stringify(sttLatency.talkspurts),
+          'stt.start_time': sttLatency.stt_start_time,
+          'stt.stop_time': sttLatency.stt_stop_time,
+          'stt.usage': sttLatency.stt_usage,
+        };
+      }
+      // time to reset the stt latency
+      this.cs.emit('transcribe-start');
       /* we've got a final transcript, so end the otel child span for this channel */
       if (this.childSpan[channel - 1] && this.childSpan[channel - 1].span) {
         this.childSpan[channel - 1].span.setAttributes({
           channel,
           'stt.label': this.label || 'None',
           'stt.resolve': 'transcript',
-          'stt.result': JSON.stringify(evt)
+          'stt.result': JSON.stringify(evt),
+          ...sttLatencyMetrics
         });
         this.childSpan[channel - 1].span.end();
       }
@@ -618,9 +641,13 @@ class TaskTranscribe extends SttTask {
     if (this.transcriptionHook) {
       const b3 = this.getTracingPropagation();
       const httpHeaders = b3 && {b3};
+      const latencies = Object.fromEntries(
+        Object.entries(sttLatencyMetrics).map(([key, value]) => [key.replace('stt.', 'stt_'), value])
+      );
       const payload = {
         ...this.cs.callInfo,
         ...httpHeaders,
+        ...latencies,
         ...(evt.alternatives && {speech: evt}),
         ...(evt.type && {speechEvent: evt})
       };

lib/utils/constants.json

@@ -177,6 +177,9 @@
   "VadDetection": {
     "Detection": "vad_detect:detection"
   },
+  "SileroVadDetection": {
+    "Detection": "vad_silero:detect"
+  },
   "ListenEvents": {
     "Connect": "mod_audio_fork::connect",
     "ConnectFailure": "mod_audio_fork::connect_failed",

lib/utils/stt-latency-calculator.js

@@ -0,0 +1,199 @@
+const { assert } = require('console');
+const Emitter = require('events');
+const {
+  VadDetection,
+  SileroVadDetection
+} = require('../utils/constants.json');
+
+class SttLatencyCalculator extends Emitter {
+  constructor({ logger, cs}) {
+    super();
+    this.logger = logger;
+    this.cs = cs;
+    this.isRunning = false;
+    this.isInTalkSpurt = false;
+    this.start_talking_time = 0;
+    this.talkspurts = [];
+    this.vendor = this.cs.vad?.vendor || 'silero';
+    this.stt_start_time = 0;
+    this.stt_stop_time = 0;
+    this.stt_on_transcription_time = 0;
+  }
+
+  set sttStartTime(time) {
+    this.stt_start_time = time;
+  }
+
+  get sttStartTime() {
+    return this.stt_start_time || 0;
+  }
+
+  set sttStopTime(time) {
+    this.stt_stop_time = time;
+  }
+
+  get sttStopTime() {
+    return this.stt_stop_time || 0;
+  }
+
+  set sttOnTranscriptionTime(time) {
+    this.stt_on_transcription_time = time;
+  }
+
+  get sttOnTranscriptionTime() {
+    return this.stt_on_transcription_time || 0;
+  }
+
+  _onVadDetected(_ep, _evt, fsEvent) {
+    if (fsEvent.getHeader('detected-event') === 'stop_talking') {
+      if (this.isInTalkSpurt) {
+        this.talkspurts.push({
+          start: this.start_talking_time,
+          stop: Date.now()
+        });
+      }
+
+      this.start_talking_time = 0;
+      this.isInTalkSpurt = false;
+    } else if (fsEvent.getHeader('detected-event') === 'start_talking') {
+      this.start_talking_time = Date.now();
+      this.isInTalkSpurt = true;
+    }
+  }
+
+  _startVad() {
+    assert(!this.isRunning, 'Latency calculator is already running');
+    assert(this.cs.ep, 'Callsession has no endpoint to start the latency calculator');
+    const ep = this.cs.ep;
+    if (!ep.sttLatencyVadHandler) {
+      ep.sttLatencyVadHandler = this._onVadDetected.bind(this, ep);
+      if (this.vendor === 'silero') {
+        ep.addCustomEventListener(SileroVadDetection.Detection, ep.sttLatencyVadHandler);
+      } else {
+        ep.addCustomEventListener(VadDetection.Detection, ep.sttLatencyVadHandler);
+      }
+    }
+    this.stop_talking_time = 0;
+    this.start_talking_time = 0;
+    this.vad = {
+      ...(this.cs.vad || {}),
+      strategy: 'continuous',
+      bugname: 'stt-latency-calculator-vad',
+      vendor: this.vendor
+    };
+
+    ep.startVadDetection(this.vad);
+    this.isRunning = true;
+  }
+
+  _stopVad() {
+    if (this.isRunning) {
+      this.logger.warn('Latency calculator is still running, stopping VAD detection');
+      const ep = this.cs.ep;
+      ep.stopVadDetection(this.vad);
+      if (ep.sttLatencyVadHandler) {
+        if (this.vendor === 'silero') {
+          this.ep?.removeCustomEventListener(SileroVadDetection.Detection, ep.sttLatencyVadHandler);
+        } else {
+          this.ep?.removeCustomEventListener(VadDetection.Detection, ep.sttLatencyVadHandler);
+        }
+        ep.sttLatencyVadHandler = null;
+      }
+      this.isRunning = false;
+      this.logger.info('STT Latency Calculator stopped');
+    } else {
+      this.logger.warn('Latency calculator is not running, no VAD detection to stop');
+    }
+  }
+
+  start() {
+    if (this.isRunning) {
+      this.logger.warn('Latency calculator is already running');
+      return;
+    }
+    if (!this.cs.ep) {
+      this.logger.error('Callsession has no endpoint to start the latency calculator');
+      return;
+    }
+    this._startVad();
+    this.logger.info('STT Latency Calculator started');
+  }
+
+  stop() {
+    this._stopVad();
+  }
+
+  toUnixTimestamp(date) {
+    return Math.floor(date / 1000);
+  }
+
+  calculateLatency() {
+    if (!this.isRunning) {
+      this.logger.debug('Latency calculator is not running, cannot calculate latency, returning default values');
+      return null;
+    }
+
+    const stt_stop_time = this.stt_stop_time || Date.now();
+    if (this.isInTalkSpurt) {
+      this.talkspurts.push({
+        start: this.start_talking_time,
+        stop: stt_stop_time
+      });
+      this.isInTalkSpurt = false;
+      this.start_talking_time = 0;
+    }
+    const stt_on_transcription_time = this.stt_on_transcription_time || stt_stop_time;
+    const start_talking_time = this.talkspurts[0]?.start;
+    let lastIdx = this.talkspurts.length - 1;
+    lastIdx = lastIdx < 0 ? 0 : lastIdx;
+    const stop_talking_time = this.talkspurts[lastIdx]?.stop || stt_stop_time;
+
+    return {
+      stt_start_time: this.toUnixTimestamp(this.stt_start_time),
+      stt_stop_time: this.toUnixTimestamp(stt_stop_time),
+      start_talking_time: this.toUnixTimestamp(start_talking_time),
+      stop_talking_time: this.toUnixTimestamp(stop_talking_time),
+      stt_latency: parseFloat((Math.abs(stt_on_transcription_time - stop_talking_time)) / 1000).toFixed(2),
+      stt_latency_ms: Math.abs(stt_on_transcription_time - stop_talking_time),
+      stt_usage: parseFloat((stt_stop_time - this.stt_start_time) / 1000).toFixed(2),
+      talkspurts: this.talkspurts.map((ts) =>
+        ([this.toUnixTimestamp(ts.start || 0), this.toUnixTimestamp(ts.stop || 0)]))
+    };
+  }
+
+  resetTime() {
+    if (!this.isRunning) {
+      return;
+    }
+    this.stt_start_time = Date.now();
+    this.stt_stop_time = 0;
+    this.stt_on_transcription_time = 0;
+    this.clearTalkspurts();
+    this.logger.info('STT Latency Calculator reset');
+  }
+
+  onTranscriptionReceived() {
+    if (!this.isRunning) {
+      return;
+    }
+    this.stt_on_transcription_time = Date.now();
+    this.logger.debug(`CallSession:on-transcription set to ${this.stt_on_transcription_time}`);
+  }
+
+  onTranscribeStop() {
+    if (!this.isRunning) {
+      return;
+    }
+    this.stt_stop_time = Date.now();
+    this.logger.debug(`CallSession:transcribe-stop set to ${this.stt_stop_time}`);
+  }
+
+  clearTalkspurts() {
+    this.talkspurts = [];
+    if (!this.isInTalkSpurt) {
+      this.start_talking_time = 0;
+    }
+  }
+}
+
+module.exports = SttLatencyCalculator;