Add enable_uso option to disable UDP segmentation offload for batched video sends

src/config.cpp

@@ -1209,6 +1209,7 @@ namespace config {
     string_f(vars, "fallback_mode", video.fallback_mode);
     bool_f(vars, "isolated_virtual_display_option", video.isolated_virtual_display_option);
     bool_f(vars, "ignore_encoder_probe_failure", video.ignore_encoder_probe_failure);
+    bool_f(vars, "enable_uso", video.enable_uso);
 
     path_f(vars, "pkey", nvhttp.pkey);
     path_f(vars, "cert", nvhttp.cert);

src/config.h

@@ -149,6 +149,15 @@ namespace config {
     std::string fallback_mode;
     bool isolated_virtual_display_option;
     bool ignore_encoder_probe_failure;
+
+    /**
+     * @brief Whether to use UDP segmentation offload (USO) when sending batched video packets on Windows.
+     *
+     * Some NIC drivers (notably VirtIO) accept the UDP_SEND_MSG_SIZE control message but silently
+     * drop the datagram instead of segmenting it, which results in no video ever reaching the client.
+     * Set to false to send video as regular MTU-sized packets instead.
+     */
+    bool enable_uso = true;
   };
 
   struct audio_t {

src/platform/common.h

@@ -674,6 +674,14 @@ namespace platf {
     uint16_t target_port;
     boost::asio::ip::address &source_address;
 
+    /**
+     * @brief Whether to use UDP segmentation offload (USO) for the batch.
+     *
+     * Only supported on Windows and only meaningful when more than one message
+     * block is sent in a single call.
+     */
+    bool enable_uso;
+
     /**
      * @brief Returns a payload buffer descriptor for the given payload offset.
      * @param offset The offset in the total payload data (bytes).

src/platform/windows/misc.cpp

@@ -1491,7 +1491,10 @@ namespace platf {
       memcpy(WSA_CMSG_DATA(cm), &pktInfo, sizeof(pktInfo));
     }
 
-    if (send_info.block_count > 1) {
+    // Only request USO when the user opted in. Some NIC drivers (notably VirtIO) accept the
+    // UDP_SEND_MSG_SIZE control message but silently drop the datagram instead of segmenting
+    // it, which breaks video streaming without any error being reported.
+    if (send_info.enable_uso && send_info.block_count > 1) {
       cmbuflen += WSA_CMSG_SPACE(sizeof(DWORD));
 
       cm = WSA_CMSG_NXTHDR(&msg, cm);

src/stream.cpp

@@ -1519,6 +1519,7 @@ namespace stream {
             peer_address,
             session->video.peer.port(),
             session->localAddress,
+            config::video.enable_uso,
           };
 
           size_t next_shard_to_send = 0;

src_assets/common/assets/web/config.html

@@ -213,6 +213,7 @@ <h1 class="my-4">{{ $t('config.configuration') }}</h1>
               "max_bitrate": 0,
               "minimum_fps_target": 0,
               "isolated_virtual_display_option": "disabled",
+              "enable_uso": "enabled",
             },
           },
           {