diff --git a/open-sse/handlers/audioTranscription.ts b/open-sse/handlers/audioTranscription.ts
index 97f08e415e..b1689ccd78 100644
--- a/open-sse/handlers/audioTranscription.ts
+++ b/open-sse/handlers/audioTranscription.ts
@@ -65,13 +65,67 @@ function getUploadedFileName(file: Blob & { name?: unknown }): string {
   return typeof file.name === "string" && file.name.length > 0 ? file.name : "audio.wav";
 }
 
+/**
+ * Infer a suitable Content-Type for Deepgram from the browser-provided MIME
+ * type and the original filename.  Deepgram accepts `audio/*` and many raw
+ * formats, but `video/*` causes it to silently fail with "no speech detected".
+ *
+ * Strategy:
+ * 1. If the browser says `audio/*`, keep it as-is.
+ * 2. If it's `video/*` (e.g. `.mp4`), remap to the audio equivalent so
+ *    Deepgram extracts the audio track.  `.mp4` → `audio/mp4`, etc.
+ * 3. Fall back to `application/octet-stream` which tells Deepgram to
+ *    auto-detect from the raw bytes (most reliable for unknown formats).
+ */
+function resolveAudioContentType(file: Blob & { name?: unknown }): string {
+  const browserType = (file.type || "").toLowerCase();
+  const fileName = typeof file.name === "string" ? file.name.toLowerCase() : "";
+
+  // 1) Browser already says it's audio — trust it
+  if (browserType.startsWith("audio/")) return browserType;
+
+  // 2) Derive from file extension (covers video/* and empty MIME)
+  const ext = fileName.includes(".") ? fileName.split(".").pop() : "";
+  const EXT_TO_MIME: Record<string, string> = {
+    mp3: "audio/mpeg",
+    mp4: "audio/mp4",
+    m4a: "audio/mp4",
+    wav: "audio/wav",
+    ogg: "audio/ogg",
+    flac: "audio/flac",
+    webm: "audio/webm",
+    aac: "audio/aac",
+    wma: "audio/x-ms-wma",
+    opus: "audio/opus",
+  };
+  if (ext && EXT_TO_MIME[ext]) return EXT_TO_MIME[ext];
+
+  // 3) Fallback — let Deepgram auto-detect from raw bytes
+  return "application/octet-stream";
+}
+
 /**
  * Handle Deepgram transcription (raw binary audio, model via query param)
  */
-async function handleDeepgramTranscription(providerConfig, file, modelId, token) {
+async function handleDeepgramTranscription(
+  providerConfig,
+  file,
+  modelId,
+  token,
+  formData?: FormData
+) {
   const url = new URL(providerConfig.baseUrl);
   url.searchParams.set("model", modelId);
   url.searchParams.set("smart_format", "true");
+  url.searchParams.set("punctuate", "true");
+
+  // Language: if caller specified one, use it; otherwise let Deepgram auto-detect
+  const langParam = formData?.get("language");
+  if (typeof langParam === "string" && langParam.trim()) {
+    url.searchParams.set("language", langParam.trim());
+  } else {
+    url.searchParams.set("detect_language", "true");
+  }
 
   const arrayBuffer = await file.arrayBuffer();
 
@@ -79,7 +133,7 @@ async function handleDeepgramTranscription(providerConfig, file, modelId, token)
     method: "POST",
     headers: {
       ...buildAuthHeaders(providerConfig, token),
-      "Content-Type": file.type || "audio/wav",
+      "Content-Type": resolveAudioContentType(file),
     },
     body: arrayBuffer,
   });
@@ -212,7 +266,7 @@ async function handleHuggingFaceTranscription(providerConfig, file, modelId, tok
     method: "POST",
     headers: {
       ...buildAuthHeaders(providerConfig, token),
-      "Content-Type": file.type || "audio/wav",
+      "Content-Type": resolveAudioContentType(file),
     },
     body: arrayBuffer,
   });
@@ -283,7 +337,7 @@ export async function handleAudioTranscription({
 
   // Route to provider-specific handler
   if (providerConfig.format === "deepgram") {
-    return handleDeepgramTranscription(providerConfig, file, modelId, token);
+    return handleDeepgramTranscription(providerConfig, file, modelId, token, formData);
   }
 
   if (providerConfig.format === "assemblyai") {
diff --git a/tsconfig.json b/tsconfig.json
index 5d6f9c9c17..515b9b1c48 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -34,7 +34,8 @@
     "**/*.js",
     "**/*.jsx",
     ".next/types/**/*.ts",
-    ".next/dev/types/**/*.ts"
+    ".next/dev/types/**/*.ts",
+    ".next/dev/dev/types/**/*.ts"
   ],
   "exclude": [
     "node_modules",