webrtcbin: Intersect codec preferences with caps from pads

When creating an offer or an answer, also take into account
the caps on the pads as well as the codec preferences when both are set.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2183>

1 files changed, 29 insertions, 9 deletions

diff --git a/ext/webrtc/gstwebrtcbin.c b/ext/webrtc/gstwebrtcbin.c
index 0994d3543..fe65041fe 100644
--- a/ext/webrtc/gstwebrtcbin.c
+++ b/ext/webrtc/gstwebrtcbin.c
@@ -1580,6 +1580,7 @@ _find_codec_preferences (GstWebRTCBin * webrtc,
 {
   WebRTCTransceiver *trans = (WebRTCTransceiver *) rtp_trans;
   GstCaps *ret = NULL;
+  GstCaps *codec_preferences = NULL;
   GstWebRTCBinPad *pad = NULL;
   GST_LOG_OBJECT (webrtc, "retrieving codec preferences from %" GST_PTR_FORMAT,
       trans);
@@ -1589,23 +1590,18 @@ _find_codec_preferences (GstWebRTCBin * webrtc,
     if (rtp_trans->codec_preferences) {
       GST_LOG_OBJECT (webrtc, "Using codec preferences: %" GST_PTR_FORMAT,
           rtp_trans->codec_preferences);
-      ret = gst_caps_ref (rtp_trans->codec_preferences);
+      codec_preferences = gst_caps_ref (rtp_trans->codec_preferences);
     }
     GST_OBJECT_UNLOCK (rtp_trans);
 
-    if (ret)
-      return ret;
+    pad = _find_pad_for_transceiver (webrtc, direction, rtp_trans);
   }
 
   /* try to find a pad */
-  if (!trans
-      || !(pad = _find_pad_for_transceiver (webrtc, direction, rtp_trans)))
+  if (!pad)
     pad = _find_pad_for_mline (webrtc, direction, media_idx);
 
-  if (!pad) {
-    if (trans && trans->last_configured_caps)
-      ret = gst_caps_ref (trans->last_configured_caps);
-  } else {
+  if (pad) {
     GstCaps *caps = NULL;
 
     if (pad->received_caps) {
@@ -1635,6 +1631,22 @@ _find_codec_preferences (GstWebRTCBin * webrtc,
       }
       gst_caps_unref (filter);
     }
+
+    if (caps && codec_preferences) {
+      GstCaps *intersection;
+
+      intersection = gst_caps_intersect_full (codec_preferences, caps,
+          GST_CAPS_INTERSECT_FIRST);
+      gst_caps_unref (caps);
+
+      if (gst_caps_is_empty (intersection)) {
+        caps = NULL;
+        gst_caps_unref (intersection);
+      } else {
+        caps = intersection;
+      }
+    }
+
     if (caps) {
       if (trans)
         gst_caps_replace (&trans->last_configured_caps, caps);
@@ -1643,8 +1655,16 @@ _find_codec_preferences (GstWebRTCBin * webrtc,
     }
 
     gst_object_unref (pad);
+  } else {
+    if (codec_preferences)
+      ret = gst_caps_ref (codec_preferences);
+    else if (trans && trans->last_configured_caps)
+      ret = gst_caps_ref (trans->last_configured_caps);
   }
 
+  if (codec_preferences)
+    gst_caps_unref (codec_preferences);
+
   if (!ret)
     GST_DEBUG_OBJECT (trans, "Could not find caps for mline %u", media_idx);