OpenVisualCloud · dmkarthi · Jul 8, 2026 · Jul 7, 2026 · Jul 8, 2026
diff --git a/README.md b/README.md
@@ -127,7 +127,7 @@ dvledtx uses a JSON config file with three sections:
 | Section | Field | Description |
 |---------|-------|-------------|
 | **log_file** | `log_file` | (Optional) Path/name of the log output file (e.g. `dvledtx.log`). If omitted, logging goes to console only. |
-| **interfaces** | `name` | PCI BDF address of the NIC (e.g. `0000:06:00.0`) |
+| **interfaces[]** | `name` | PCI BDF address of the NIC (e.g. `0000:06:00.0`) |
 | | `sip` | Source IP address |
 | | `dip` | Destination multicast IP address |
 | **video** | `width` | Source frame width in pixels |
@@ -137,26 +137,31 @@ dvledtx uses a JSON config file with three sections:
 | | `scale_height` | (Optional) Output height after scaling |
 | | `fps` | Frames per second (25, 30, 50, 60) |
 | | `fmt` | Pixel format (see [Supported Formats](#supported-formats)) |
-| **tx_sessions[]** | `udp_port` | UDP port for the session |
+| **tx_sessions[]** | `nic_index` | (Optional) Index into `interfaces[]` selecting which NIC this session uses (default: `0`) |
+| | `udp_port` | UDP port for the session |
 | | `payload_type` | (Optional) RTP payload type — defaults to `96` if not present |
 | | `crop` | Region to transmit: `x`, `y`, `w`, `h` in pixels |
 
-Example (`config/tx_fullhd_single_session.json`):
+Example (`config/tx_fullhd_multi_nic.json`):
 ```json
 {
   "log_file": "dvledtx.log",
   "interfaces": [
-    { "name": "0000:06:00.0", "sip": "192.168.50.29", "dip": "239.168.85.20" }
+    { "name": "0000:03:10.0", "sip": "192.168.50.30", "dip": "239.168.85.20" },
+    { "name": "0000:03:10.2", "sip": "192.168.50.29", "dip": "239.168.85.21" }
   ],
   "video": {
     "width": 1920, "height": 1080,
     "tx_url": "bbb_sunflower_1080p_30fps_normal.mp4"
   },
   "tx_video": {
-    "fps": 30, "fmt": "yuv422p10le"
+    "scale_width": 1920, "scale_height": 1080,
+    "fps": 30,
+    "fmt": "yuv422p10le"
   },
   "tx_sessions": [
-    { "udp_port": 20000, "crop": { "x": 0, "y": 0, "w": 1920, "h": 1080 } }
+    { "nic_index": 0, "udp_port": 20000, "payload_type": 96, "crop": { "x": 0,   "y": 0, "w": 960, "h": 1080 } },
+    { "nic_index": 1, "udp_port": 20002, "payload_type": 96, "crop": { "x": 960, "y": 0, "w": 960, "h": 1080 } }
   ]
 }
 ```
@@ -265,7 +270,7 @@ Example — upscale 1080p source to 4K output:
     "fps": 30, "fmt": "yuv422p10le"
   },
   "tx_sessions": [
-    { "udp_port": 20000, "crop": { "x": 0, "y": 0, "w": 3840, "h": 2160 } }
+    { "udp_port": 20000, "payload_type": 96, "crop": { "x": 0, "y": 0, "w": 3840, "h": 2160 } }
   ]
 }
 ```

diff --git a/config/tx_2k_multi_session.json b/config/tx_2k_multi_session.json
@@ -2,15 +2,15 @@
   "log_file": "dvledtx.log",
   "interfaces": [
     {
-      "name": "0000:06:00.0",
+      "name": "0000:03:00.1",
       "sip":  "192.168.50.29",
       "dip":  "239.168.85.20"
     }
   ],
   "video": {
     "width":  2560,
     "height": 1440,
-    "tx_url": "bbb_sunflower_1080p_30fps_normal.mp4"
+    "tx_url": "ball_2k_yuv420p_30fps_5min.mp4"
   },
   "tx_video": {
     "scale_width":  2560,
@@ -21,14 +21,17 @@
   "tx_sessions": [
     {
       "udp_port":     20000,
+      "payload_type": 96,
       "crop": { "x": 0,    "y": 0, "w": 854, "h": 1440 }
     },
     {
       "udp_port":     20002,
+      "payload_type": 96,
       "crop": { "x": 854,  "y": 0, "w": 854, "h": 1440 }
     },
     {
       "udp_port":     20004,
+      "payload_type": 96,
       "crop": { "x": 1708, "y": 0, "w": 852, "h": 1440 }
     }
   ]

diff --git a/config/tx_2k_single_session.json b/config/tx_2k_single_session.json
@@ -10,7 +10,7 @@
   "video": {
     "width":  2560,
     "height": 1440,
-    "tx_url": "ball_2k_yuv420p_30fps_5min.mp4"
+    "tx_url": "ball_2k_yuv422p10_30fps_5min.mp4"
   },
   "tx_video": {
     "scale_width":  2560,

diff --git a/config/tx_4k_multi_session.json b/config/tx_4k_multi_session.json
@@ -10,7 +10,7 @@
   "video": {
     "width":  3840,
     "height": 2160,
-    "tx_url": "ball_4k_gbrp10le_60fps_5min.mp4"
+    "tx_url": "ball_4k_yuv422p10_60fps_5min.mp4"
   },
   "tx_video": {
     "scale_width":  1920,
@@ -21,14 +21,17 @@
   "tx_sessions": [
     {
       "udp_port":     20000,
+      "payload_type": 96,
       "crop": { "x": 0,    "y": 0, "w": 640, "h": 1080 }
     },
     {
       "udp_port":     20002,
+      "payload_type": 96,
       "crop": { "x": 640, "y": 0, "w": 640, "h": 1080 }
     },
     {
       "udp_port":     20004,
+      "payload_type": 96,
       "crop": { "x": 1280, "y": 0, "w": 640, "h": 1080 }
     }
   ]

diff --git a/config/tx_4k_single_session.json b/config/tx_4k_single_session.json
@@ -10,17 +10,18 @@
   "video": {
     "width":  3840,
     "height": 2160,
-    "tx_url": "ball_4k_gbrp10le_60fps_5min.mp4"
+    "tx_url": "ball_4k_yuv422p10_60fps_5min.mp4"
   },
   "tx_video": {
     "scale_width":  900,
     "scale_height": 600,
-    "fps":    30,
+    "fps":    60,
     "fmt":    "yuv422p10le"
   },
   "tx_sessions": [
     {
       "udp_port":     20000,
+      "payload_type": 96,
       "crop": { "x": 0, "y": 0, "w": 900, "h": 600 }
     }
   ]

diff --git a/config/tx_fullhd_multi_nic.json b/config/tx_fullhd_multi_nic.json
@@ -0,0 +1,67 @@
+{
+  "log_file": "dvledtx.log",
+  "interfaces": [
+    {
+      "name": "0000:03:10.0",
+      "sip":  "192.168.50.30",
+      "dip":  "239.168.85.20"
+    },
+    {
+      "name": "0000:03:10.2",
+      "sip":  "192.168.50.31",
+      "dip":  "239.168.85.21"
+    },
+    {
+      "name": "0000:03:10.4",
+      "sip":  "192.168.50.32",
+      "dip":  "239.168.85.22"
+    },
+    {
+      "name": "0000:03:10.6",
+      "sip":  "192.168.50.33",
+      "dip":  "239.168.85.23"
+    },
+    {
+      "name": "0000:03:11.0",
+      "sip":  "192.168.50.34",
+      "dip":  "239.168.85.24"
+    },
+    {
+      "name": "0000:03:11.2",
+      "sip":  "192.168.50.35",
+      "dip":  "239.168.85.25"
+    }
+  ],
+  "video": {
+    "width":  1920,
+    "height": 1080,
+    "tx_url": "ball_fullhd_yuv422p10_30fps_5min.mp4"
+  },
+  "tx_video": {
+    "scale_width":  1920,
+    "scale_height": 1080,
+    "fps":    30,
+    "fmt":    "yuv422p10le"
+  },
+  "tx_sessions": [
+    {
+      "nic_index": 0,
+      "udp_port":  20000,
+      "payload_type": 96,
+      "crop": { "x": 0,    "y": 0, "w": 640, "h": 1080 }
+    },
+    {
+      "nic_index": 1,
+      "udp_port":  20002,
+      "payload_type": 96,
+      "crop": { "x": 640,  "y": 0, "w": 640, "h": 1080 }
+    },
+    {
+      "nic_index": 2,
+      "udp_port":  20004,
+      "payload_type": 96,
+      "crop": { "x": 1280, "y": 0, "w": 640, "h": 1080 }
+    }
+  ]
+}
+
diff --git a/config/tx_fullhd_multi_session.json b/config/tx_fullhd_multi_session.json
@@ -2,15 +2,15 @@
   "log_file": "dvledtx.log",
   "interfaces": [
     {
-      "name": "0000:06:00.0",
+      "name": "0000:03:10.1",
       "sip":  "192.168.50.29",
-      "dip":  "239.168.85.20"
+      "dip":  "239.168.85.21"
     }
   ],
   "video": {
     "width":  1920,
     "height": 1080,
-    "tx_url": "bbb_sunflower_1080p_30fps_normal.mp4"
+    "tx_url": "ball_fullhd_yuv422p10_30fps_5min.mp4"
   },
   "tx_video": {
     "scale_width":  1920,
@@ -21,14 +21,17 @@
   "tx_sessions": [
     {
       "udp_port":     20000,
+      "payload_type": 96,
       "crop": { "x": 0,    "y": 0, "w": 640, "h": 1080 }
     },
     {
       "udp_port":     20002,
+      "payload_type": 96,
       "crop": { "x": 640,  "y": 0, "w": 640, "h": 1080 }
     },
     {
       "udp_port":     20004,
+      "payload_type": 96,
       "crop": { "x": 1280, "y": 0, "w": 640, "h": 1080 }
     }
   ]

diff --git a/config/tx_fullhd_single_session.json b/config/tx_fullhd_single_session.json
@@ -10,7 +10,7 @@
   "video": {
     "width":  3840,
     "height": 2160,
-    "tx_url": "bbb_sunflower_1080p_30fps_normal.mp4"
+    "tx_url": "ball_fullhd_yuv422p10_30fps_5min.mp4"
   },
   "tx_video": {
     "scale_width":  3840,
@@ -21,6 +21,7 @@
   "tx_sessions": [
     {
       "udp_port":     20000,
+      "payload_type": 96,
       "crop": { "x": 0, "y": 0, "w": 1920, "h": 1080 }
     }
   ]

diff --git a/include/app_context.h b/include/app_context.h
@@ -6,10 +6,24 @@
 
 #include <stdint.h>
 #include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
 #include <arpa/inet.h>
 #include <libavutil/pixfmt.h>
 
-#define MAX_TX_SESSIONS (8)
+/* Fixed field-width constants (not array size limits) */
+#define PORT_NAME_LEN     64
+#define IP_STR_LEN        INET_ADDRSTRLEN
+#define IP_ADDR_BYTES     4
+
+/* Per-NIC configuration (one element per interface) */
+struct nic_config {
+  char    port[PORT_NAME_LEN];        /* DPDK NIC PCI BDF */
+  char    sip_addr_str[IP_STR_LEN];   /* source IP string */
+  uint8_t sip_addr[IP_ADDR_BYTES];    /* source IP binary */
+  char    dip_addr_str[IP_STR_LEN];   /* destination IP string */
+  uint8_t dip_addr[IP_ADDR_BYTES];    /* destination IP binary */
+};
 
 /* Per-session network and crop parameters (populated from JSON tx_sessions[]) */
 struct tx_session_net {
@@ -19,18 +33,17 @@ struct tx_session_net {
   int      crop_y;
   int      crop_w;
   int      crop_h;
+  int      nic_index;   /* which NIC this session uses (index into nics[]) */
 };
 
 /* Application context for TX sessions */
 struct dvledtx_context {
-  /* Configuration */
-  char port[64];        /* DPDK NIC PCI BDF/address for MTL output (e.g. 0000:af:00.0), not a Linux interface name */
+  /* NIC configuration — dynamically allocated array [0..nic_count-1] */
+  int              nic_count;          /* number of active NICs */
+  struct nic_config* nics;             /* heap-allocated, nic_count elements */
+
   char tx_url[256];
   char config_file[256];
-  char sip_addr_str[INET_ADDRSTRLEN];
-  uint8_t sip_addr[4];
-  char dip_addr_str[INET_ADDRSTRLEN];
-  uint8_t dip_addr[4];
   uint16_t udp_port;
   uint8_t  payload_type;  /* RTP dynamic payload type (default: 96) */
 
@@ -48,10 +61,47 @@ struct dvledtx_context {
   bool force_dhcp;
   int test_time_s;
 
-  /* Per-session network + crop config (from JSON tx_sessions[]) */
-  struct tx_session_net session_net[MAX_TX_SESSIONS];
+  /* Per-session network + crop config — dynamically allocated, st20p_sessions elements */
+  struct tx_session_net* session_net;
 
   /* Optional log file path from config (empty = console logging only) */
   char log_file[256];
 
 };
+
+/* Free dynamically allocated members of dvledtx_context (nics, session_net).
+ * Does NOT free the struct itself (it may be stack-allocated). */
+static inline void dvledtx_context_free(struct dvledtx_context* ctx) {
+  if (ctx == NULL) return;
+  free(ctx->nics);        ctx->nics = NULL;
+  free(ctx->session_net); ctx->session_net = NULL;
+  ctx->nic_count = 0;
+  ctx->st20p_sessions = 0;
+}
+
+/* Allocate NIC and session arrays inside an already zeroed context.
+ * calloc(0, ...) is permitted by the C standard to return NULL, which is
+ * not an allocation failure, so a zero count is treated as "nothing to
+ * allocate" rather than an error (avoids spurious failures, e.g. in tests
+ * that call dvledtx_context_alloc(ctx, 1, 0)). On failure, ctx is left
+ * fully zeroed (no dangling nics pointer with a stale nic_count) so it
+ * remains safe to pass to dvledtx_context_free().
+ * Returns 0 on success, -1 on allocation failure. */
+static inline int dvledtx_context_alloc(struct dvledtx_context* ctx,
+                                        int nic_count, int session_count) {
+  if (nic_count > 0) {
+    ctx->nics = calloc((size_t)nic_count, sizeof(struct nic_config));
+    if (ctx->nics == NULL) return -1;
+  }
+  ctx->nic_count = nic_count;
+
+  if (session_count > 0) {
+    ctx->session_net = calloc((size_t)session_count, sizeof(struct tx_session_net));
+    if (ctx->session_net == NULL) {
+      free(ctx->nics); ctx->nics = NULL; ctx->nic_count = 0;
+      return -1;
+    }
+  }
+  ctx->st20p_sessions = session_count;
+  return 0;
+}
diff --git a/include/core/session_manager.h b/include/core/session_manager.h
@@ -16,9 +16,11 @@
 #include <libavutil/imgutils.h>
 #include <libswscale/swscale.h>
 
-/* MTL pipeline API headers — only when building the direct MTL TX path */
-#ifdef ENABLE_MTL_TX
+/* MTL API headers — always included; mtl_tx_init/uninit are always compiled
+ * to allow pre-initialising all NIC ports regardless of TX path. */
 #include "mtl_api.h"
+
+#ifdef ENABLE_MTL_TX
 #include "st_pipeline_api.h"
 #endif
 
@@ -120,9 +122,7 @@ typedef struct session_manager_s {
 
   struct shared_decode_ctx* shared_dec;
 
-#ifdef ENABLE_MTL_TX
   mtl_handle mtl;   /* MTL library instance — owns all st20p_tx sessions */
-#endif
 
   bool running;
 } session_manager_t;