configure: fix build with --disable-external
diff --git a/configure.ac b/configure.ac
index 4ce095f..96aed92 100644
--- a/configure.ac
+++ b/configure.ac
@@ -197,6 +197,7 @@
 AG_GST_PKG_CHECK_MODULES(GST_AUDIO, gstreamer-audio-[$GST_API_VERSION], [$GST_REQ], yes)
 AG_GST_PKG_CHECK_MODULES(GST_PBUTILS, gstreamer-pbutils-[$GST_API_VERSION], [$GST_REQ], yes)
 AG_GST_PKG_CHECK_MODULES(GST_GL, gstreamer-gl-[$GST_API_VERSION], [$GST_REQ], no)
+AG_GST_PKG_CHECK_MODULES(GST_SDP, gstreamer-sdp-[$GST_API_VERSION], [$GST_REQ], yes)
 
 if test "x$HAVE_GST_GL" = "xyes"; then
 
@@ -2295,7 +2296,6 @@
 dnl *** WebRTC ***
 translit(dnm, m, l) AM_CONDITIONAL(USE_WEBRTC, true)
 AG_GST_CHECK_FEATURE(WEBRTC, [WebRTC], webrtc, [
-  AG_GST_PKG_CHECK_MODULES(GST_SDP, gstreamer-sdp-1.0)
   PKG_CHECK_MODULES(NICE, nice >= 0.1, [
     HAVE_WEBRTC="yes" ], [
     HAVE_WEBRTC="no"
@@ -2320,6 +2320,7 @@
 AM_CONDITIONAL(USE_DC1394, false)
 AM_CONDITIONAL(USE_DECKLINK, false)
 AM_CONDITIONAL(DECKLINK_OSX, false)
+AM_CONDITIONAL(DECKLINK_WIN, false)
 AM_CONDITIONAL(USE_DIRECTFB, false)
 AM_CONDITIONAL(USE_WAYLAND, false)
 AM_CONDITIONAL(USE_DAALA, false)
@@ -2332,6 +2333,7 @@
 AM_CONDITIONAL(USE_FDK_AAC, false)
 AM_CONDITIONAL(USE_FLITE, false)
 AM_CONDITIONAL(USE_FLUIDSYNTH, false)
+AM_CONDITIONAL(USE_GL, false)
 AM_CONDITIONAL(USE_GSM, false)
 AM_CONDITIONAL(USE_HLS, false)
 AM_CONDITIONAL(USE_IQA, false)
@@ -2352,6 +2354,7 @@
 AM_CONDITIONAL(USE_OPENAL, false)
 AM_CONDITIONAL(USE_OPENCV, false)
 AM_CONDITIONAL(USE_OPENEXR, false)
+AM_CONDITIONAL(USE_OPENGL, false)
 AM_CONDITIONAL(USE_OPENJPEG, false)
 AM_CONDITIONAL(USE_OPENMPT, false)
 AM_CONDITIONAL(USE_OPENNI2, false)
@@ -2363,6 +2366,7 @@
 AM_CONDITIONAL(USE_SPANDSP, false)
 AM_CONDITIONAL(USE_SPC, false)
 AM_CONDITIONAL(USE_SRTP, false)
+AM_CONDITIONAL(USE_SRT, false)
 AM_CONDITIONAL(USE_GME, false)
 AM_CONDITIONAL(USE_DVB, false)
 AM_CONDITIONAL(USE_ACM, false)