rtsp-server: fix for creating backchannel stream dynamically

If collecting the backchannel stream after the stream has begun
preparing, make sure to join it to the RTSP media bin, as is
done for dynamic payloaders in the pad-added handler. Add a
new internal stream creation method for it, that could be
publically exposed later if it proves useful.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8378>

subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-media.c

@@ -2747,6 +2747,35 @@ gst_rtsp_media_create_stream (GstRTSPMedia * media, GstElement * payloader,
   return stream;
 }
 
+GstRTSPStream *
+gst_rtsp_media_create_and_join_stream (GstRTSPMedia * media,
+    GstElement * payloader, GstPad * pad)
+{
+  GstRTSPStream *stream = gst_rtsp_media_create_stream (media, payloader, pad);
+  GstRTSPMediaPrivate *priv = media->priv;
+
+  if (stream == NULL) {
+    return NULL;
+  }
+
+  g_rec_mutex_lock (&priv->state_lock);
+  if (priv->status == GST_RTSP_MEDIA_STATUS_PREPARING) {
+    /* join the element in the PAUSED state because this callback is
+     * called from the streaming thread and it is PAUSED */
+    if (!gst_rtsp_stream_join_bin (stream, GST_BIN (priv->pipeline),
+            priv->rtpbin, GST_STATE_PAUSED)) {
+      GST_WARNING ("failed to join bin element");
+    }
+
+    if (priv->blocked)
+      gst_rtsp_stream_set_blocked (stream, TRUE);
+  }
+
+  g_rec_mutex_unlock (&priv->state_lock);
+
+  return stream;
+}
+
 static void
 gst_rtsp_media_remove_stream (GstRTSPMedia * media, GstRTSPStream * stream)
 {

subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-onvif-media.c

@@ -43,6 +43,7 @@
 
 #include "rtsp-onvif-media.h"
 #include "rtsp-latency-bin.h"
+#include "rtsp-server-internal.h"
 
 GST_DEBUG_CATEGORY_STATIC (rtsp_onvif_media_debug);
 #define GST_CAT_DEFAULT rtsp_onvif_media_debug
@@ -317,7 +318,8 @@ gst_rtsp_onvif_media_collect_backchannel (GstRTSPOnvifMedia * media)
     goto out;
 
   GST_LOG_OBJECT (media, "Creating backchannel stream");
-  gst_rtsp_media_create_stream (GST_RTSP_MEDIA (media), latency_bin, pad);
+  gst_rtsp_media_create_and_join_stream (GST_RTSP_MEDIA (media), latency_bin,
+      pad);
   ret = TRUE;
 
 out:

subprojects/gst-rtsp-server/gst/rtsp-server/rtsp-server-internal.h

@@ -67,6 +67,10 @@ void                     gst_rtsp_stream_set_drop_delta_units (GstRTSPStream * s
 
 gboolean                 gst_rtsp_stream_install_drop_probe (GstRTSPStream * stream);
 
+GstRTSPStream *          gst_rtsp_media_create_and_join_stream (GstRTSPMedia * media,
+                                                                GstElement * payloader,
+                                                                GstPad * pad);
+
 G_END_DECLS
 
 #endif /* __GST_RTSP_SERVER_INTERNAL_H__ */