feat(rtsp): add option to limit packetsize for clients that cannot configure it (#5153)

Signed-off-by: Georgi Valkov <gvalkov@gmail.com>

src/config.cpp

@@ -544,6 +544,7 @@ namespace config {
 
     ENCRYPTION_MODE_NEVER,  // lan_encryption_mode
     ENCRYPTION_MODE_OPPORTUNISTIC,  // wan_encryption_mode
+    0,  // packetsize
   };
 
   nvhttp_t nvhttp {
@@ -1252,6 +1253,7 @@ namespace config {
 
     int_between_f(vars, "lan_encryption_mode", stream.lan_encryption_mode, {0, 2});
     int_between_f(vars, "wan_encryption_mode", stream.wan_encryption_mode, {0, 2});
+    int_between_f(vars, "packetsize", stream.packetsize, {0, PACKETSIZE_MAX});
 
     path_f(vars, "file_apps", stream.file_apps);
 #ifndef __ANDROID__

src/config.h

@@ -16,6 +16,12 @@
 #include "nvenc/nvenc_config.h"
 
 namespace config {
+  // Valid range for the packetsize limit
+  constexpr int PACKETSIZE_MIN = 200;
+  constexpr int PACKETSIZE_MAX = 65535;
+  constexpr int PACKETSIZE_SMALL = 500;
+  constexpr int PACKETSIZE_LARGE = 1456;
+
   // track modified config options
   inline std::unordered_map<std::string, std::string> modified_config_settings;
 
@@ -177,6 +183,9 @@ namespace config {
     // Video encryption settings for LAN and WAN streams
     int lan_encryption_mode;
     int wan_encryption_mode;
+
+    // Limit the packetsize to avoid fragmentation on a low MTU link
+    int packetsize;
   };
 
   struct nvhttp_t {

src/rtsp.cpp

@@ -1004,6 +1004,23 @@ namespace rtsp_stream {
         config.encryptionFlagsEnabled |= SS_ENC_AUDIO;
       }
 
+      // Limit the packetsize to avoid fragmentation with clients that cannot configure this value
+      if (config::stream.packetsize && config::stream.packetsize < config.packetsize) {
+        if (config::stream.packetsize < config::PACKETSIZE_MIN || config::stream.packetsize > config::PACKETSIZE_MAX) {
+          BOOST_LOG(warning) << "packetsize range: ["sv << config::PACKETSIZE_MIN << "-"sv << config::PACKETSIZE_MAX
+                             << "] invalid value: "sv << config::stream.packetsize;
+        } else {
+          if (config::stream.packetsize < config::PACKETSIZE_SMALL) {
+            BOOST_LOG(info) << "packetsize is small < "sv << config::PACKETSIZE_SMALL << " bytes, reduce bitrate if the stream breaks"sv;
+          } else if (config::stream.packetsize > config::PACKETSIZE_LARGE) {
+            BOOST_LOG(info) << "packetsize is large > "sv << config::PACKETSIZE_LARGE << " bytes, jumbo frames may be used"sv;
+          }
+
+          BOOST_LOG(info) << "packetsize limit: "sv << config.packetsize << " -> "sv << config::stream.packetsize << " bytes"sv;
+          config.packetsize = config::stream.packetsize;
+        }
+      }
+
       config.monitor.height = (int) util::from_view(args.at("x-nv-video[0].clientViewportHt"sv));
       config.monitor.width = (int) util::from_view(args.at("x-nv-video[0].clientViewportWd"sv));
       config.monitor.framerate = (int) util::from_view(args.at("x-nv-video[0].maxFPS"sv));