From: Taran Nathan <moogoesmeow123@gmail.com>
Date: Tue, 21 Jul 2026 19:58:25 +0000 (-0700)
Subject: speech recognition
X-Git-Url: https://git.taranathan.com/?a=commitdiff_plain;h=7bacd98a86bda5178f98e4b1b1a889da94c9689e;p=audio-stream.git

speech recognition
---

diff --git a/index.html b/index.html
index e2cad11..1ee9d54 100644
--- a/index.html
+++ b/index.html
@@ -18,6 +18,8 @@
     <button id="btnPlay" disabled>PLAY RECORDING</button>
   </p>
   <audio id="audioPlay"></audio>
+  <p id="transcription">
+  </p>
 </body>
 
 </html>
\ No newline at end of file
diff --git a/script.js b/script.js
index ec65453..c1a1991 100644
--- a/script.js
+++ b/script.js
@@ -6,13 +6,46 @@ let systemStream;
 let mixedAudioStream;
 let audioContext;
 let mixedDestination;
+let transcriptionSocket;
+let streamSourceNode;
+let streamProcessorNode;
+let streamMuteNode;
+let committedTranscription = "";
+let partialTranscription = "";
 
 const startButton = document.getElementById("btnStart");
 const stopButton = document.getElementById("btnStop");
 const playButton = document.getElementById("btnPlay");
 const audioElement = document.getElementById("audioPlay");
+const transcriptionElement = document.getElementById("transcription");
+
+const BACKEND_WS_URL = "ws://localhost:3000/ws/transcribe";
+const CHUNK_MS = 3000;
+const TARGET_SAMPLE_RATE = 16000;
+
+function renderTranscription() {
+  const committed = committedTranscription.trim();
+  const partial = partialTranscription.trim();
+
+  if (!committed && !partial) {
+    transcriptionElement.textContent = "";
+    return;
+  }
+
+  transcriptionElement.textContent = partial ? `${committed} ${partial}`.trim() : committed;
+}
+
+function cleanupCaptureResources(closeTranscriptionSocket = true) {
+  if (streamProcessorNode) {
+    streamProcessorNode.disconnect();
+  }
+  if (streamSourceNode) {
+    streamSourceNode.disconnect();
+  }
+  if (streamMuteNode) {
+    streamMuteNode.disconnect();
+  }
 
-function cleanupCaptureResources() {
   [microphoneStream, systemStream, mixedAudioStream].forEach((stream) => {
     if (stream) {
       stream.getTracks().forEach((track) => track.stop());
@@ -23,15 +56,187 @@ function cleanupCaptureResources() {
     audioContext.close();
   }
 
+  if (closeTranscriptionSocket && transcriptionSocket && transcriptionSocket.readyState === WebSocket.OPEN) {
+    transcriptionSocket.close();
+  }
+
   microphoneStream = null;
   systemStream = null;
   mixedAudioStream = null;
   audioContext = null;
   mixedDestination = null;
+  streamSourceNode = null;
+  streamProcessorNode = null;
+  streamMuteNode = null;
+  if (closeTranscriptionSocket) {
+    transcriptionSocket = null;
+  }
+}
+
+function appendCommittedTranscription(text) {
+  if (!text) {
+    return;
+  }
+
+  const trimmedText = text.trim();
+  if (!trimmedText) {
+    return;
+  }
+
+  committedTranscription = committedTranscription
+    ? `${committedTranscription} ${trimmedText}`
+    : trimmedText;
+  partialTranscription = "";
+  renderTranscription();
+}
+
+function updatePartialTranscription(text) {
+  const trimmedText = text?.trim() || "";
+  partialTranscription = trimmedText;
+  renderTranscription();
+}
+
+function extractTranscriptFromRealtimeEvent(payload) {
+  if (!payload || typeof payload !== "object") {
+    return null;
+  }
+
+  if (typeof payload.error === "string") {
+    return {
+      kind: "error",
+      text: payload.error
+    };
+  }
+
+  const typeValue = typeof payload.type === "string" ? payload.type.toLowerCase() : "";
+  const finalByType =
+    typeValue.includes("termination") ||
+    typeValue.includes("final") ||
+    typeValue.includes("completed");
+
+  const candidates = [
+    payload.text,
+    payload.transcript,
+    payload.delta,
+    payload.partial,
+    payload.final,
+    payload.turn?.text,
+    payload.turn?.transcript,
+    payload.turn?.final,
+    payload.result?.text,
+    payload.result?.transcript
+  ];
+
+  const transcriptText = candidates.find((value) => typeof value === "string" && value.trim());
+  if (!transcriptText) {
+    return null;
+  }
+
+  return {
+    kind: finalByType || payload.is_final === true || payload.final === true ? "final" : "partial",
+    text: transcriptText
+  };
+}
+
+function downsampleToTargetSampleRate(float32Samples, inputSampleRate, targetSampleRate) {
+  if (targetSampleRate >= inputSampleRate) {
+    return float32Samples;
+  }
+
+  const ratio = inputSampleRate / targetSampleRate;
+  const outputLength = Math.round(float32Samples.length / ratio);
+  const result = new Float32Array(outputLength);
+
+  let outputIndex = 0;
+  let inputIndex = 0;
+  while (outputIndex < outputLength) {
+    const nextInputIndex = Math.round((outputIndex + 1) * ratio);
+    let total = 0;
+    let count = 0;
+
+    for (let i = inputIndex; i < nextInputIndex && i < float32Samples.length; i += 1) {
+      total += float32Samples[i];
+      count += 1;
+    }
+
+    result[outputIndex] = count > 0 ? total / count : 0;
+    outputIndex += 1;
+    inputIndex = nextInputIndex;
+  }
+
+  return result;
+}
+
+function float32ToPcm16Buffer(float32Samples) {
+  const arrayBuffer = new ArrayBuffer(float32Samples.length * 2);
+  const dataView = new DataView(arrayBuffer);
+
+  for (let i = 0; i < float32Samples.length; i += 1) {
+    const clamped = Math.max(-1, Math.min(1, float32Samples[i]));
+    const int16Value = clamped < 0 ? clamped * 0x8000 : clamped * 0x7fff;
+    dataView.setInt16(i * 2, int16Value, true);
+  }
+
+  return arrayBuffer;
+}
+
+function connectTranscriptionSocket() {
+  return new Promise((resolve, reject) => {
+    const socket = new WebSocket(BACKEND_WS_URL);
+    socket.binaryType = "arraybuffer";
+
+    socket.addEventListener("open", () => {
+      transcriptionSocket = socket;
+      resolve(socket);
+    });
+
+    socket.addEventListener("message", (event) => {
+      if (typeof event.data !== "string") {
+        return;
+      }
+
+      let parsed;
+      try {
+        parsed = JSON.parse(event.data);
+      } catch {
+        return;
+      }
+
+      const transcriptEvent = extractTranscriptFromRealtimeEvent(parsed);
+      if (!transcriptEvent) {
+        return;
+      }
+
+      if (transcriptEvent.kind === "error") {
+        console.error("Realtime transcription error:", transcriptEvent.text);
+        return;
+      }
+
+      if (transcriptEvent.kind === "final") {
+        appendCommittedTranscription(transcriptEvent.text);
+      } else {
+        updatePartialTranscription(transcriptEvent.text);
+      }
+    });
+
+    socket.addEventListener("error", (event) => {
+      reject(new Error(`Transcription socket error: ${event.type}`));
+    });
+
+    socket.addEventListener("close", () => {
+      if (transcriptionSocket === socket) {
+        transcriptionSocket = null;
+      }
+    });
+  });
 }
 
 startButton.addEventListener("click", async () => {
   try {
+    committedTranscription = "";
+    partialTranscription = "";
+    renderTranscription();
+
     microphoneStream = await navigator.mediaDevices.getUserMedia({ audio: true });
     systemStream = await navigator.mediaDevices.getDisplayMedia({
       video: true,
@@ -41,7 +246,7 @@ startButton.addEventListener("click", async () => {
     console.log(systemStream.getTracks());
 
     if (systemStream.getAudioTracks().length === 0) {
-      console.error( "No screen share audio track. Microphone only." );
+      console.error("No screen share audio track. Microphone only.");
       systemStream.getTracks().forEach((track) => track.stop());
       systemStream = null;
     }
@@ -57,7 +262,44 @@ startButton.addEventListener("click", async () => {
     }
 
     mixedAudioStream = mixedDestination.stream;
-    mediaRecorder = new MediaRecorder(mixedAudioStream);
+    await connectTranscriptionSocket();
+
+    streamSourceNode = audioContext.createMediaStreamSource(mixedAudioStream);
+    streamProcessorNode = audioContext.createScriptProcessor(4096, 1, 1);
+    streamMuteNode = audioContext.createGain();
+    streamMuteNode.gain.value = 0;
+
+    streamSourceNode.connect(streamProcessorNode);
+    streamProcessorNode.connect(streamMuteNode);
+    streamMuteNode.connect(audioContext.destination);
+
+    streamProcessorNode.onaudioprocess = (audioProcessEvent) => {
+      if (!transcriptionSocket || transcriptionSocket.readyState !== WebSocket.OPEN) {
+        return;
+      }
+
+      const channelSamples = audioProcessEvent.inputBuffer.getChannelData(0);
+      const downsampled = downsampleToTargetSampleRate(
+        channelSamples,
+        audioContext.sampleRate,
+        TARGET_SAMPLE_RATE
+      );
+      const pcm16Buffer = float32ToPcm16Buffer(downsampled);
+      transcriptionSocket.send(pcm16Buffer);
+    };
+
+    const preferredMimeTypes = [
+      "audio/webm;codecs=opus",
+      "audio/webm",
+      "audio/ogg;codecs=opus",
+      "audio/ogg"
+    ];
+    const selectedMimeType = preferredMimeTypes.find((type) => MediaRecorder.isTypeSupported(type));
+    console.log("selected mime type:", selectedMimeType);
+    mediaRecorder = selectedMimeType
+      ? new MediaRecorder(mixedAudioStream, { mimeType: selectedMimeType })
+      : new MediaRecorder(mixedAudioStream);
+    //Array<Blob>
     audioChunks = [];
 
     mediaRecorder.addEventListener("dataavailable", (event) => {
@@ -66,9 +308,9 @@ startButton.addEventListener("click", async () => {
       }
     });
 
-    mediaRecorder.addEventListener("stop", async () => {
-      const audioBlob = new Blob(audioChunks, { type: "audio/ogg" });
-      console.log(await audioBlob.text());
+    mediaRecorder.addEventListener("stop", () => {
+      const audioBlob = new Blob(audioChunks, { type: mediaRecorder.mimeType || "audio/webm" });
+      console.log(audioBlob)
 
       if (recordedAudioUrl) {
         URL.revokeObjectURL(recordedAudioUrl);
@@ -79,10 +321,20 @@ startButton.addEventListener("click", async () => {
       audioElement.src = recordedAudioUrl;
       playButton.disabled = false;
 
-      cleanupCaptureResources();
+      const socketToClose = transcriptionSocket;
+      if (socketToClose && socketToClose.readyState === WebSocket.OPEN) {
+        socketToClose.send(JSON.stringify({ type: "Terminate" }));
+        setTimeout(() => {
+          if (socketToClose.readyState === WebSocket.OPEN) {
+            socketToClose.close();
+          }
+        }, 1500);
+      }
+
+      cleanupCaptureResources(false);
     });
 
-    mediaRecorder.start();
+    mediaRecorder.start(CHUNK_MS);
     startButton.disabled = true;
     stopButton.disabled = false;
     playButton.disabled = true;
@@ -100,6 +352,10 @@ stopButton.addEventListener("click", () => {
     return;
   }
 
+  if (transcriptionSocket && transcriptionSocket.readyState === WebSocket.OPEN) {
+    transcriptionSocket.send(JSON.stringify({ type: "Terminate" }));
+  }
+
   mediaRecorder.stop();
   stopButton.disabled = true;
   startButton.disabled = false;
diff --git a/transcription-backend/.gitignore b/transcription-backend/.gitignore
new file mode 100644
index 0000000..a145785
--- /dev/null
+++ b/transcription-backend/.gitignore
@@ -0,0 +1,3 @@
+build
+.env
+
diff --git a/transcription-backend/Cargo.lock b/transcription-backend/Cargo.lock
new file mode 100644
index 0000000..d35c31e
--- /dev/null
+++ b/transcription-backend/Cargo.lock
@@ -0,0 +1,1106 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
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+ "log",
+ "pin-project-lite",
+ "tracing-core",
+]
+
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+ "once_cell",
+]
+
+[[package]]
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+version = "0.1.0"
+dependencies = [
+ "axum",
+ "dotenvy",
+ "futures-util",
+ "serde",
+ "serde_json",
+ "tokio",
+ "tokio-tungstenite 0.27.0",
+ "tower-http",
+]
+
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+dependencies = [
+ "bytes",
+ "data-encoding",
+ "http",
+ "httparse",
+ "log",
+ "native-tls",
+ "rand",
+ "sha1",
+ "thiserror",
+ "utf-8",
+]
+
+[[package]]
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+dependencies = [
+ "bytes",
+ "data-encoding",
+ "http",
+ "httparse",
+ "log",
+ "rand",
+ "sha1",
+ "thiserror",
+]
+
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+ "wit-bindgen",
+]
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+ "windows-link",
+]
+
+[[package]]
+name = "wit-bindgen"
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+dependencies = [
+ "zerocopy-derive",
+]
+
+[[package]]
+name = "zerocopy-derive"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.119",
+]
+
+[[package]]
+name = "zmij"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
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diff --git a/transcription-backend/Cargo.toml b/transcription-backend/Cargo.toml
new file mode 100644
index 0000000..c235065
--- /dev/null
+++ b/transcription-backend/Cargo.toml
@@ -0,0 +1,14 @@
+[package]
+name = "transcription-backend"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+axum = { version = "0.8.9", features = ["macros", "multipart", "ws"] }
+futures-util = "0.3.31"
+serde = { version = "1.0.229", features = ["derive"] }
+serde_json = "1.0.151"
+tokio = { version = "1.48.0", features = ["macros", "rt-multi-thread"] }
+tokio-tungstenite = { version = "0.27.0", features = ["native-tls"] }
+tower-http = { version = "0.6.6", features = ["cors"] }
+dotenvy = "0.15.7"
diff --git a/transcription-backend/src/main.rs b/transcription-backend/src/main.rs
new file mode 100644
index 0000000..92e9a00
--- /dev/null
+++ b/transcription-backend/src/main.rs
@@ -0,0 +1,238 @@
+use std::{env, net::SocketAddr, sync::Arc};
+
+use axum::{
+    Router,
+    extract::{
+        State,
+        ws::{Message, WebSocket, WebSocketUpgrade},
+    },
+    response::IntoResponse,
+    routing::get,
+};
+use dotenvy::dotenv;
+use futures_util::{SinkExt, StreamExt};
+use serde::Serialize;
+use tokio_tungstenite::{
+    connect_async,
+    tungstenite::{Message as UpstreamMessage, client::IntoClientRequest},
+};
+use tower_http::cors::{Any, CorsLayer};
+
+#[derive(Clone)]
+struct AppState {
+    whisper_api_key: Arc<String>,
+    whisper_api_base: Arc<String>,
+}
+
+#[derive(Serialize)]
+struct HealthResponse<'a> {
+    status: &'a str,
+}
+
+#[tokio::main]
+async fn main() {
+    dotenv().ok();
+
+    let whisper_api_key = env::var("WHISPER_API_KEY")
+        .expect("WHISPER_API_KEY is required (server-side API key, starts with wai_)");
+    let whisper_api_base =
+        env::var("WHISPER_API_URL").unwrap_or_else(|_| "https://api.whisperai.com".to_string());
+
+    let state = AppState {
+        whisper_api_key: Arc::new(whisper_api_key),
+        whisper_api_base: Arc::new(whisper_api_base),
+    };
+
+    let cors = CorsLayer::new()
+        .allow_origin(Any)
+        .allow_headers(Any)
+        .allow_methods(Any);
+
+    let app = Router::new()
+        .route("/health", get(health))
+        .route("/ws/transcribe", get(ws_transcribe))
+        .with_state(state)
+        .layer(cors);
+
+    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
+    let listener = tokio::net::TcpListener::bind(addr)
+        .await
+        .expect("failed to bind TCP listener");
+
+    println!("Transcription backend listening on http://{addr}");
+    axum::serve(listener, app)
+        .await
+        .expect("axum server failed");
+}
+
+async fn health() -> impl IntoResponse {
+    axum::Json(HealthResponse { status: "ok" })
+}
+
+async fn ws_transcribe(ws: WebSocketUpgrade, State(state): State<AppState>) -> impl IntoResponse {
+    ws.on_upgrade(move |socket| proxy_ws_to_whisper(socket, state))
+}
+
+fn build_upstream_ws_url(base_url: &str) -> Result<String, String> {
+    let trimmed = base_url.trim().trim_end_matches('/');
+    let without_v1 = trimmed.strip_suffix("/v1").unwrap_or(trimmed);
+
+    let ws_base = if let Some(rest) = without_v1.strip_prefix("https://") {
+        format!("wss://{rest}")
+    } else if let Some(rest) = without_v1.strip_prefix("http://") {
+        format!("ws://{rest}")
+    } else if without_v1.starts_with("wss://") || without_v1.starts_with("ws://") {
+        without_v1.to_string()
+    } else {
+        return Err("WHISPER_API_URL must start with http(s):// or ws(s)://".to_string());
+    };
+
+    Ok(format!(
+        "{ws_base}/v1/realtime/ws?speech_model=whisperai-realtime-pro&encoding=pcm_s16le&sample_rate=16000&format_turns=true&speaker_labels=true"
+    ))
+}
+
+async fn proxy_ws_to_whisper(client_socket: WebSocket, state: AppState) {
+    let upstream_ws_url = match build_upstream_ws_url(&state.whisper_api_base) {
+        Ok(url) => url,
+        Err(error_message) => {
+            let mut socket = client_socket;
+            let _ = socket.send(Message::Text(error_message.into())).await;
+            let _ = socket.close().await;
+            return;
+        }
+    };
+
+    let mut request = match upstream_ws_url.into_client_request() {
+        Ok(request) => request,
+        Err(error) => {
+            let mut socket = client_socket;
+            let _ = socket
+                .send(Message::Text(
+                    format!("Failed to build upstream WS request: {error}").into(),
+                ))
+                .await;
+            let _ = socket.close().await;
+            return;
+        }
+    };
+
+    let auth_header = match state.whisper_api_key.parse() {
+        Ok(header) => header,
+        Err(error) => {
+            let mut socket = client_socket;
+            let _ = socket
+                .send(Message::Text(
+                    format!("Invalid WHISPER_API_KEY header value: {error}").into(),
+                ))
+                .await;
+            let _ = socket.close().await;
+            return;
+        }
+    };
+    request.headers_mut().insert("Authorization", auth_header);
+
+    let (upstream_socket, _) = match connect_async(request).await {
+        Ok(result) => result,
+        Err(error) => {
+            let mut socket = client_socket;
+            let _ = socket
+                .send(Message::Text(
+                    format!("Failed to connect to Whisper realtime API: {error}").into(),
+                ))
+                .await;
+            let _ = socket.close().await;
+            return;
+        }
+    };
+
+    let (mut client_tx, mut client_rx) = client_socket.split();
+    let (mut upstream_tx, mut upstream_rx) = upstream_socket.split();
+
+    let client_to_upstream = async {
+        while let Some(message_result) = client_rx.next().await {
+            let message = match message_result {
+                Ok(message) => message,
+                Err(error) => {
+                    return Err(format!("Client socket read error: {error}"));
+                }
+            };
+
+            let upstream_message = match message {
+                Message::Binary(bytes) => UpstreamMessage::Binary(bytes),
+                Message::Text(text) => UpstreamMessage::Text(text.to_string().into()),
+                Message::Ping(bytes) => UpstreamMessage::Ping(bytes),
+                Message::Pong(bytes) => UpstreamMessage::Pong(bytes),
+                Message::Close(frame) => {
+                    let close_frame =
+                        frame.map(|f| tokio_tungstenite::tungstenite::protocol::CloseFrame {
+                            code: f.code.into(),
+                            reason: f.reason.to_string().into(),
+                        });
+                    let _ = upstream_tx.send(UpstreamMessage::Close(close_frame)).await;
+                    return Ok(());
+                }
+            };
+
+            if let Err(error) = upstream_tx.send(upstream_message).await {
+                return Err(format!("Upstream socket write error: {error}"));
+            }
+        }
+
+        let _ = upstream_tx
+            .send(UpstreamMessage::Text(
+                "{\"type\":\"Terminate\"}".to_string().into(),
+            ))
+            .await;
+        let _ = upstream_tx.send(UpstreamMessage::Close(None)).await;
+        Ok(())
+    };
+
+    let upstream_to_client = async {
+        while let Some(message_result) = upstream_rx.next().await {
+            let message = match message_result {
+                Ok(message) => message,
+                Err(error) => {
+                    return Err(format!("Upstream socket read error: {error}"));
+                }
+            };
+
+            let client_message = match message {
+                UpstreamMessage::Binary(bytes) => Message::Binary(bytes),
+                UpstreamMessage::Text(text) => Message::Text(text.to_string().into()),
+                UpstreamMessage::Ping(bytes) => Message::Ping(bytes),
+                UpstreamMessage::Pong(bytes) => Message::Pong(bytes),
+                UpstreamMessage::Close(frame) => {
+                    let close_frame = frame.map(|f| axum::extract::ws::CloseFrame {
+                        code: f.code.into(),
+                        reason: f.reason.to_string().into(),
+                    });
+                    let _ = client_tx.send(Message::Close(close_frame)).await;
+                    return Ok(());
+                }
+                UpstreamMessage::Frame(_) => continue,
+            };
+
+            if let Err(error) = client_tx.send(client_message).await {
+                return Err(format!("Client socket write error: {error}"));
+            }
+        }
+
+        Ok(())
+    };
+
+    tokio::select! {
+        result = client_to_upstream => {
+            if let Err(error_message) = result {
+                let _ = client_tx.send(Message::Text(error_message.into())).await;
+            }
+            let _ = client_tx.close().await;
+        }
+        result = upstream_to_client => {
+            if let Err(error_message) = result {
+                let _ = client_tx.send(Message::Text(error_message.into())).await;
+            }
+            let _ = client_tx.close().await;
+        }
+    }
+}