diff --git a/services/web-ui/public/modal-new-recorder.jsx b/services/web-ui/public/modal-new-recorder.jsx
index 5f74584..652028d 100644
--- a/services/web-ui/public/modal-new-recorder.jsx
+++ b/services/web-ui/public/modal-new-recorder.jsx
@@ -232,7 +232,11 @@ function NewRecorderModal({ open, onClose }) {
     } else if (sourceType === 'RTMP') {
       body.source_config = { url: rtmpUrl };
     } else if (sourceType === 'DELTACAST') {
-      body.source_config = {};
+      // One Deltacast board (index 0) exposes 8 channels. The picker's selected
+      // index IS the capture channel, so persist it as source_config.port; the
+      // capture sidecar maps that to the bridge's --port. device_index is kept
+      // for backward-compatible display/fallback.
+      body.source_config = { port: dcDeviceIdx };
       body.device_index = dcDeviceIdx;
       body.node_id = dcNodeId || undefined;
     } else {