Use different RTX payload types for different H264 profiles

webrtc/media/engine/webrtcvideoengine2.cc

Index: webrtc/media/engine/webrtcvideoengine2.cc
diff --git a/webrtc/media/engine/webrtcvideoengine2.cc b/webrtc/media/engine/webrtcvideoengine2.cc
index 2ebbd78e9861e837e0a37335794c3a0a7aef1be5..0b8c761170a38d3f19d12870bc68ac287ceeac70 100644
--- a/webrtc/media/engine/webrtcvideoengine2.cc
+++ b/webrtc/media/engine/webrtcvideoengine2.cc
@@ -22,6 +22,7 @@
 #include "webrtc/base/timeutils.h"
 #include "webrtc/base/trace_event.h"
 #include "webrtc/call.h"
+#include "webrtc/common_video/h264/profile_level_id.h"
 #include "webrtc/media/engine/constants.h"
 #include "webrtc/media/engine/simulcast.h"
 #include "webrtc/media/engine/webrtcmediaengine.h"
@@ -403,7 +404,18 @@ void AddCodecAndMaybeRtxCodec(const VideoCodec& codec,
   } else if (CodecNamesEq(codec.name, kVp9CodecName)) {
     rtx_payload_type = kDefaultRtxVp9PlType;
   } else if (CodecNamesEq(codec.name, kH264CodecName)) {
-    rtx_payload_type = kDefaultRtxH264PlType;
+    // Parse H264 profile.
+    const rtc::Optional<webrtc::H264::ProfileLevelId> profile_level_id =
+        webrtc::H264::ParseSdpProfileLevelId(codec.params);
+    if (!profile_level_id)
+      return;
+    const webrtc::H264::Profile profile = profile_level_id->profile;
+    // Only supported rtx for constrained baseline and constrained high profile.

[hta-webrtc, 2016/11/15 10:41:07]

Grammar nit: "In H.264, we only support rtx for constrained baseline and
constrained high profile."

[magjed_webrtc, 2016/11/15 17:48:04]

Done.

+    if (profile == webrtc::H264::kProfileConstrainedBaseline) {
+      rtx_payload_type = kDefaultRtxH264ConstrainedBaselinePlType;
+    } else if (profile == webrtc::H264::kProfileConstrainedHigh) {
+      rtx_payload_type = kDefaultRtxH264ConstrainedHighPlType;
+    }

[hta-webrtc, 2016/11/15 10:41:07]

"Else" missing - if this is neither of the two above, it will fall through to
the "codecs->push_back" at the bottom with rtx_payload_type uninitialized.

I'm assuming the "else" should be "return" like the others.

Please add an unit test covering a profile for which RTX is not supported.

[magjed_webrtc, 2016/11/15 17:48:04]

Done.

   } else if (CodecNamesEq(codec.name, kRedCodecName)) {
     rtx_payload_type = kDefaultRtxRedPlType;
   } else {