Choose RTX codec PT in lower range if codec is in lower range

pc1 video mline without this change (and the previous one):
96 97 107 108 109 114 115 116 117 118 119 120 37 121 40 124 98 99 100 101 127 42 43
with this change:
96 97 103 104 107 108 109 114 115 116 117 118 39 40 45 46 98 99 100 101 119 120 121

BUG=webrtc:360058654

Change-Id: I4021daf1c62f0edf9650e12a74619035040291a8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/376022
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43838}

call/BUILD.gn

diff --git a/call/BUILD.gn b/call/BUILD.gn
index 8f37af0..484b772 100644
--- a/call/BUILD.gn
+++ b/call/BUILD.gn
@@ -396,6 +396,7 @@
     "../media:media_constants",
     "../rtc_base:checks",
     "../rtc_base:logging",
+    "../rtc_base:stringutils",
     "../rtc_base:strong_alias",
     "//third_party/abseil-cpp/absl/strings",
   ]

call/payload_type_picker.cc

diff --git a/call/payload_type_picker.cc b/call/payload_type_picker.cc
index eb8ed45..c7983ce 100644
--- a/call/payload_type_picker.cc
+++ b/call/payload_type_picker.cc
@@ -25,6 +25,7 @@
 #include "media/base/media_constants.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/logging.h"
+#include "rtc_base/string_encode.h"
 
 namespace webrtc {
 
@@ -80,6 +81,15 @@
         return true;
       }
     }
+  } else if (absl::EqualsIgnoreCase(codec.name, cricket::kRtxCodecName)) {
+    // For RTX prefer lower range if the associated codec is in that range.
+    std::string associated_pt_str;
+    int associated_pt;
+    return codec.GetParam(cricket::kCodecParamAssociatedPayloadType,
+                          &associated_pt_str) &&
+           rtc::FromString(associated_pt_str, &associated_pt) &&
+           associated_pt >= kFirstDynamicPayloadTypeLowerRange &&
+           associated_pt <= kLastDynamicPayloadTypeLowerRange;
   }
   return false;
 }

call/payload_type_picker_unittest.cc

diff --git a/call/payload_type_picker_unittest.cc b/call/payload_type_picker_unittest.cc
index fd64923..5a3e39b 100644
--- a/call/payload_type_picker_unittest.cc
+++ b/call/payload_type_picker_unittest.cc
@@ -10,6 +10,7 @@
 
 #include "call/payload_type_picker.h"
 
+#include "api/video_codecs/sdp_video_format.h"
 #include "call/payload_type.h"
 #include "media/base/codec.h"
 #include "media/base/media_constants.h"
@@ -205,9 +206,14 @@
   // Valid for high range only.
   EXPECT_THAT(picker.SuggestMapping(h264_constrained, nullptr).value(), Ge(96));
   EXPECT_THAT(picker.SuggestMapping(vp9_profile_2, nullptr).value(), Ge(96));
-  // Valud for lower range.
+  // Valid for lower range.
   EXPECT_THAT(picker.SuggestMapping(h264_yuv444, nullptr).value(), Lt(63));
   EXPECT_THAT(picker.SuggestMapping(vp9_profile_3, nullptr).value(), Lt(63));
+
+  // RTX with a primary codec in the lower range is valid for lower range.
+  cricket::Codec lower_range_rtx =
+      cricket::CreateVideoRtxCodec(cricket::Codec::kIdNotSet, 63);
+  EXPECT_THAT(picker.SuggestMapping(lower_range_rtx, nullptr).value(), Lt(63));
 }
 
 TEST(PayloadTypePicker, ChoosingH264Profiles) {