Get the indx header value with key field from msg. The result in value stays valid as long as it remains present in msg.
a #GstRTSPHeaderField
pointer to hold the result
the index of the header
#GST_RTSP_OK when field was found, #GST_RTSP_ENOTIMPL if the key was not found.
Get the indx header value with key field from msg. The result in value stays valid as long as it remains present in msg.