diff --git a/.changes/stalker-mpv-header-comma-escape.md b/.changes/stalker-mpv-header-comma-escape.md
new file mode 100644
index 000000000..e6612cd18
--- /dev/null
+++ b/.changes/stalker-mpv-header-comma-escape.md
@@ -0,0 +1,10 @@
+---
+type: fix
+area: playback
+---
+
+Stalker live TV plays again in the embedded MPV player. The MAG250 user agent
+contains a comma (`KHTML, like Gecko`), which MPV splits in its comma-separated
+`--http-header-fields` list, truncating `X-User-Agent` so strict portals reject
+the stream with HTTP 400. Commas and backslashes in header values are now
+escaped on the Windows/Linux and macOS embedded-MPV paths.
diff --git a/apps/electron-backend/native/src/embedded_mpv.mm b/apps/electron-backend/native/src/embedded_mpv.mm
index 76cf6cf2c..54e7730d2 100644
--- a/apps/electron-backend/native/src/embedded_mpv.mm
+++ b/apps/electron-backend/native/src/embedded_mpv.mm
@@ -766,6 +766,19 @@ void onRenderContextUpdate(void* context)
     }
 }
 
+void replaceAllInPlace(std::string& value, const std::string& from, const std::string& to)
+{
+    if (from.empty()) {
+        return;
+    }
+
+    size_t position = 0;
+    while ((position = value.find(from, position)) != std::string::npos) {
+        value.replace(position, from.length(), to);
+        position += to.length();
+    }
+}
+
 std::string joinHeaderFields(const Napi::Object& headers)
 {
     const Napi::Array propertyNames = headers.GetPropertyNames();
@@ -789,6 +802,15 @@ std::string joinHeaderFields(const Napi::Object& headers)
             continue;
         }
 
+        // mpv's `--http-header-fields` option is a comma-separated list
+        // (OPT_STRINGLIST). Header values that themselves contain commas
+        // (e.g. the Stalker MAG250 user agent "...(KHTML, like Gecko) MAG250")
+        // must be escaped so mpv does not split them into bogus fields and
+        // the server rejects the request with HTTP 400. mpv strips the
+        // backslash and keeps the comma inside the header value.
+        replaceAllInPlace(value, "\\", "\\\\");
+        replaceAllInPlace(value, ",", "\\,");
+
         fields.push_back(key + ": " + value);
     }
 
diff --git a/apps/electron-backend/native/src/embedded_mpv_wid_common.h b/apps/electron-backend/native/src/embedded_mpv_wid_common.h
index 814e1153a..507d62305 100644
--- a/apps/electron-backend/native/src/embedded_mpv_wid_common.h
+++ b/apps/electron-backend/native/src/embedded_mpv_wid_common.h
@@ -289,6 +289,19 @@ std::string normalizeEnvValue(const char* value)
     return result;
 }
 
+void replaceAllInPlace(std::string& value, const std::string& from, const std::string& to)
+{
+    if (from.empty()) {
+        return;
+    }
+
+    size_t position = 0;
+    while ((position = value.find(from, position)) != std::string::npos) {
+        value.replace(position, from.length(), to);
+        position += to.length();
+    }
+}
+
 std::string joinHeaderFields(const Napi::Object& headers)
 {
     const Napi::Array propertyNames = headers.GetPropertyNames();
@@ -312,6 +325,15 @@ std::string joinHeaderFields(const Napi::Object& headers)
             continue;
         }
 
+        // mpv's `--http-header-fields` option is a comma-separated list
+        // (OPT_STRINGLIST). Header values that themselves contain commas
+        // (e.g. the Stalker MAG250 user agent "...(KHTML, like Gecko) MAG250")
+        // must be escaped so mpv does not split them into bogus fields and
+        // the server rejects the request with HTTP 400. mpv strips the
+        // backslash and keeps the comma inside the header value.
+        replaceAllInPlace(value, "\\", "\\\\");
+        replaceAllInPlace(value, ",", "\\,");
+
         fields.push_back(key + ": " + value);
     }