Optimize transcription speed: remove artificial delays, add timing

- AWS Transcribe: remove 10ms delay between chunks (was adding ~1.25s/MB),
  increase chunk size from 8KB to 32KB (AWS max per frame)
- Add detailed timing logs (ffmpeg, streaming, total) for diagnostics
- OpenAI Whisper: use response_format='text' for faster response parsing
- Frontend: show transcription time in toast, request 16kHz sample rate,
  increase bitrate to 32kbps Opus (better quality, still small files)
- Return duration in API response for all providers

public/js/app.js

@@ -454,11 +454,12 @@ function createTimer(el) {
 function AudioRecorder() { this.mediaRecorder = null; this.chunks = []; this.stream = null; }
 AudioRecorder.prototype.start = function() {
   var self = this; self.chunks = [];
-  return navigator.mediaDevices.getUserMedia({ audio: { channelCount: 1, echoCancellation: true, noiseSuppression: true } })
+  return navigator.mediaDevices.getUserMedia({ audio: { channelCount: 1, sampleRate: 16000, echoCancellation: true, noiseSuppression: true } })
   .then(function(stream) {
     self.stream = stream;
     var mime = MediaRecorder.isTypeSupported('audio/webm;codecs=opus') ? 'audio/webm;codecs=opus' : 'audio/webm';
-    self.mediaRecorder = new MediaRecorder(stream, { mimeType: mime, audioBitsPerSecond: 16000 });
+    // 32kbps Opus is excellent for speech — small files, fast upload, great quality
+    self.mediaRecorder = new MediaRecorder(stream, { mimeType: mime, audioBitsPerSecond: 32000 });
     self.mediaRecorder.ondataavailable = function(e) { if (e.data.size > 0) self.chunks.push(e.data); };
     self.mediaRecorder.start(1000);
   });
@@ -482,6 +483,7 @@ AudioRecorder.prototype.stop = function() {
 };
 
 function transcribeAudio(blob) {
+  var startTime = Date.now();
   var formData = new FormData();
   formData.append('audio', blob, 'audio.webm');
   return fetch('/api/transcribe', {
@@ -489,8 +491,9 @@ function transcribeAudio(blob) {
     headers: { 'Authorization': 'Bearer ' + (window.AUTH_TOKEN || localStorage.getItem('ped_scribe_token') || '') },
     body: formData
   }).then(function(r) { return r.json(); }).then(function(data) {
+    var elapsed = ((Date.now() - startTime) / 1000).toFixed(1);
     if (data.success && data.provider) {
-      showToast('Transcribed via ' + data.provider, 'info');
+      showToast('Transcribed via ' + data.provider + ' (' + elapsed + 's)', 'info');
     }
     // Delete audio backup on successful transcription
     if (data.success && window._lastAudioBackupId) {

src/routes/transcribe.js

@@ -30,10 +30,14 @@ console.log('🎙️  Transcribe provider:', provider + (provider === 'aws' && m
 router.post('/transcribe', authMiddleware, upload.single('audio'), async (req, res) => {
   try {
     if (!req.file) return res.status(400).json({ error: 'No audio' });
+    var startTime = Date.now();
+    var fileSize = req.file.size;
+    console.log('[Transcribe] Received ' + (fileSize / 1024).toFixed(0) + 'KB audio (' + (req.file.mimetype || 'unknown') + ') via ' + provider);
 
     if (provider === 'local') {
       var text = await transcribeWithLocal(req.file.buffer, req.file.mimetype || 'audio/webm');
-      return res.json({ success: true, text: text, provider: 'local-whisper' });
+      console.log('[Transcribe] Local done in ' + (Date.now() - startTime) + 'ms');
+      return res.json({ success: true, text: text, provider: 'local-whisper', duration: Date.now() - startTime });
     }
 
     if (provider === 'aws') {
@@ -41,7 +45,8 @@ router.post('/transcribe', authMiddleware, upload.single('audio'), async (req, r
         return res.status(400).json({ error: 'AWS Transcribe not configured. Set AWS_BEDROCK_REGION.' });
       }
       var text = await transcribeWithAWS(req.file.buffer, req.file.mimetype || 'audio/webm');
-      return res.json({ success: true, text: text, provider: 'aws-transcribe' });
+      console.log('[Transcribe] AWS done in ' + (Date.now() - startTime) + 'ms');
+      return res.json({ success: true, text: text, provider: 'aws-transcribe', duration: Date.now() - startTime });
     }
 
     // OpenAI Whisper
@@ -49,10 +54,14 @@ router.post('/transcribe', authMiddleware, upload.single('audio'), async (req, r
     var file = new File([req.file.buffer], 'audio.webm', { type: req.file.mimetype || 'audio/webm' });
     var result = await whisperClient.audio.transcriptions.create({
       file, model: 'whisper-1', language: 'en',
+      response_format: 'text',
       prompt: 'Medical patient encounter. Pediatric. Clinical terms, diagnoses, medications.'
     });
-    res.json({ success: true, text: result.text, provider: 'openai-whisper' });
+    var text = typeof result === 'string' ? result : result.text;
+    console.log('[Transcribe] Whisper done in ' + (Date.now() - startTime) + 'ms');
+    res.json({ success: true, text: text, provider: 'openai-whisper', duration: Date.now() - startTime });
   } catch (err) {
+    console.error('[Transcribe] Error:', err.message);
     res.status(500).json({ error: err.message });
   }
 });

src/utils/transcribeAWS.js

@@ -59,10 +59,11 @@ function convertToPCM(inputBuffer) {
 }
 
 async function* makeAudioStream(buffer) {
-  for (var i = 0; i < buffer.length; i += CHUNK_SIZE) {
+  // Send chunks as fast as possible — AWS handles backpressure via HTTP/2 flow control.
-    yield { AudioEvent: { AudioChunk: buffer.slice(i, i + CHUNK_SIZE) } };
+  // Larger chunks (32KB) reduce overhead and speed up streaming significantly.
-    // Small delay between chunks to prevent overwhelming the stream
+  var streamChunkSize = 32768; // 32 KB (AWS max per event frame)
-    await new Promise(function(r) { setTimeout(r, 10); });
+  for (var i = 0; i < buffer.length; i += streamChunkSize) {
+    yield { AudioEvent: { AudioChunk: buffer.slice(i, i + streamChunkSize) } };
   }
 }
 
@@ -82,6 +83,7 @@ function logTranscribeError(label, err) {
 }
 
 async function transcribeWithAWS(audioBuffer, mimeType) {
+  var startTime = Date.now();
   var TranscribeModule = require('@aws-sdk/client-transcribe-streaming');
   var TranscribeStreamingClient = TranscribeModule.TranscribeStreamingClient;
 
@@ -98,10 +100,11 @@ async function transcribeWithAWS(audioBuffer, mimeType) {
   var sampleRate = 48000;
 
   try {
+    var ffStart = Date.now();
     audioToSend = await convertToPCM(audioBuffer);
     mediaEncoding = 'pcm';
     sampleRate = 16000;
-    console.log('[Transcribe] ffmpeg conversion OK — PCM 16kHz, ' + audioToSend.length + ' bytes');
+    console.log('[Transcribe] ffmpeg: ' + (Date.now() - ffStart) + 'ms — ' + audioBuffer.length + ' → ' + audioToSend.length + ' bytes');
   } catch (ffErr) {
     console.warn('[Transcribe] ffmpeg unavailable, sending ogg-opus directly:', ffErr.message);
     if (mimeType && mimeType.indexOf('wav') !== -1) {
@@ -138,6 +141,7 @@ async function transcribeWithAWS(audioBuffer, mimeType) {
   }
 
   // Try Medical first if enabled, with fallback to Standard
+  var streamStart = Date.now();
   if (useMedical) {
     try {
       var client = new TranscribeStreamingClient({ region: region, credentials: credentials });
@@ -151,10 +155,11 @@ async function transcribeWithAWS(audioBuffer, mimeType) {
       });
       var medResp = await client.send(medCmd);
       transcript = await collectTranscript(medResp.TranscriptResultStream);
-      console.log('[Transcribe] Medical OK (' + transcript.length + ' chars)');
+      console.log('[Transcribe] Medical OK — ' + (Date.now() - streamStart) + 'ms, ' + transcript.length + ' chars');
     } catch (medErr) {
       logTranscribeError('Medical failed', medErr);
       console.warn('[Transcribe] Falling back to standard...');
+      streamStart = Date.now();
       try {
         var client2 = new TranscribeStreamingClient({ region: region, credentials: credentials });
         var stdCmd = new TranscribeModule.StartStreamTranscriptionCommand({
@@ -165,7 +170,7 @@ async function transcribeWithAWS(audioBuffer, mimeType) {
         });
         var stdResp = await client2.send(stdCmd);
         transcript = await collectTranscript(stdResp.TranscriptResultStream);
-        console.log('[Transcribe] Standard fallback OK (' + transcript.length + ' chars)');
+        console.log('[Transcribe] Standard fallback OK — ' + (Date.now() - streamStart) + 'ms, ' + transcript.length + ' chars');
       } catch (stdErr) {
         logTranscribeError('Standard also failed', stdErr);
         throw stdErr;
@@ -181,9 +186,10 @@ async function transcribeWithAWS(audioBuffer, mimeType) {
     });
     var resp = await client.send(cmd);
     transcript = await collectTranscript(resp.TranscriptResultStream);
-    console.log('[Transcribe] Standard OK (' + transcript.length + ' chars)');
+    console.log('[Transcribe] Standard OK — ' + (Date.now() - streamStart) + 'ms, ' + transcript.length + ' chars');
   }
 
+  console.log('[Transcribe] Total: ' + (Date.now() - startTime) + 'ms');
   return transcript.trim();
 }