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gst_parse_launch there is no proper conversion function from string to gchar

September 13, 2022

I have a simple code with c++ using gstreamer to read rtsp video.
I’m new to gstreamer, I couldn’t concatenate gst_parse_launch() with a URL_RTSP variable for my rtsp links.

here is no variable URL_RTSP, that works:

  /* Build the pipeline */
  pipeline = gst_parse_launch("rtspsrc protocols=tcp location=rtsp://user:pass@protocol:port/cam/realmonitor?channel=1&subtype=0 latency=300 ! decodebin3 ! autovideosink", NULL);

  /* Start playing */
  gst_element_set_state (pipeline, GST_STATE_PLAYING);

with the variable URL_RTSP, doesn’t work:

  /*Url Cams*/
  std::string URL_RTSP = "rtsp://user:pass@protocol:port/cam/realmonitor?channel=1&subtype=0";

  /* Build the pipeline */
  pipeline =
      gst_parse_launch("rtspsrc protocols=tcp location="+ URL_RTSP + " latency=300 ! decodebin3 ! autovideosink", NULL);

  /* Start playing */
  gst_element_set_state (pipeline, GST_STATE_PLAYING);

Error when I try to use with variable, gst_parse_launch() get the error:

there is no proper conversion function from "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" to "const gchar *"

>Solution :

gst_parse_launch takes a const gchar* as the first argument:

GstElement* gst_parse_launch (const gchar* pipeline_description, GError** error)

But, what you provide,

"rtspsrc protocols=tcp location="+ URL_RTSP + 
" latency=300 ! decodebin3 ! autovideosink"

results in a std::string. I suggest creating the std::string first, then use the c_str() member function to pass it a const char*.

std::string tmp =
    "rtspsrc protocols=tcp location=" + URL_RTSP +
    " latency=300 ! decodebin3 ! autovideosink";

pipeline = gst_parse_launch(tmp.c_str(), nullptr);