commit c262375415c369f3cd6bc92bf9e2689f1064fb55
author Henrik Boström <hbos@webrtc.org> Mon Feb 03 13:18:23 2025
committer WebRTC LUCI CQ <webrtc-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon Feb 03 14:11:53 2025
tree 1e95e59b167b86c1d7a0d56c7774cea24054cbe8
parent ae248075905c29a43320542d458f49515bb7f741

Add test for preferring RTX payload to be "primary codec + 1".

Adds test coverage for the following mitigations (need both to pass):
1. https://webrtc-review.googlesource.com/c/src/+/375847
2. https://webrtc-review.googlesource.com/c/src/+/376022

Like the comment says, this is neither mandated by the spec or
guaranteed, but when the number of codecs is quite small like it is in
this test it will be true for all RTX codecs.

Bug: webrtc:360058654
Change-Id: Ib73cea59d06a62390dd039eb2dc04677d6178460
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/375865
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43841}

media/engine/webrtc_video_engine_unittest.cc

diff --git a/media/engine/webrtc_video_engine_unittest.cc b/media/engine/webrtc_video_engine_unittest.cc
index a76b209d..911a34b 100644
--- a/media/engine/webrtc_video_engine_unittest.cc
+++ b/media/engine/webrtc_video_engine_unittest.cc
@@ -471,6 +471,34 @@
   FAIL() << "No RTX codec found among default codecs.";
 }
 
+// Test that we prefer to assign RTX payload types as "primary codec PT + 1".
+// This is purely for backwards compatibility (see https://crbug.com/391132280).
+// The spec does NOT mandate we do this and note that this is best-effort, if
+// "PT + 1" is already in-use the PT suggester would pick a different PT.
+TEST_F(WebRtcVideoEngineTest,
+       DefaultRtxCodecIsAssignedAssociatedPayloadTypePlusOne) {
+  AddSupportedVideoCodecType("VP8");
+  AddSupportedVideoCodecType("VP9");
+  AddSupportedVideoCodecType("AV1");
+  AddSupportedVideoCodecType("H264");
+  for (const Codec& codec : engine_.send_codecs()) {
+    if (codec.name != kRtxCodecName)
+      continue;
+    int associated_payload_type;
+    ASSERT_TRUE(codec.GetParam(kCodecParamAssociatedPayloadType,
+                               &associated_payload_type));
+    EXPECT_EQ(codec.id, associated_payload_type + 1);
+  }
+  for (const Codec& codec : engine_.recv_codecs()) {
+    if (codec.name != kRtxCodecName)
+      continue;
+    int associated_payload_type;
+    ASSERT_TRUE(codec.GetParam(kCodecParamAssociatedPayloadType,
+                               &associated_payload_type));
+    EXPECT_EQ(codec.id, associated_payload_type + 1);
+  }
+}
+
 TEST_F(WebRtcVideoEngineTest, SupportsTimestampOffsetHeaderExtension) {
   ExpectRtpCapabilitySupport(RtpExtension::kTimestampOffsetUri, true);
 }