From 48f4498801595ea5d2e3fac4fa4e29521461ff0c Mon Sep 17 00:00:00 2001
From: =?utf8?q?Olivier=20Cr=C3=AAte?= <olivier.crete@collabora.com>
Date: Fri, 30 Apr 2021 17:04:12 -0400
Subject: [PATCH] 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>
---
 ext/webrtc/gstwebrtcbin.c | 38 +++++++++++++++++++++++++++++---------
 1 file changed, 29 insertions(+), 9 deletions(-)

diff --git a/ext/webrtc/gstwebrtcbin.c b/ext/webrtc/gstwebrtcbin.c
index 0994d35..fe65041 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);
 
-- 
2.7.4