Let PCF.GetRtpSenderCapabilities return codecs' scalabilityModes.

Also move ScalabilityModeToString to api and add RTC_EXPORT so that
Chromium can use it.

Bug: chromium:986069
Change-Id: I5dbbb6de9b14ca20f3ae0630552dcd44595ad5ef
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/267780
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Daniel.L (Byoungchan) Lee <daniel.l@hpcnt.com>
Cr-Commit-Position: refs/heads/main@{#37444}
diff --git a/api/video_codecs/BUILD.gn b/api/video_codecs/BUILD.gn
index 1671af1..0b6db87 100644
--- a/api/video_codecs/BUILD.gn
+++ b/api/video_codecs/BUILD.gn
@@ -14,7 +14,15 @@
 
 rtc_source_set("scalability_mode") {
   visibility = [ "*" ]
-  sources = [ "scalability_mode.h" ]
+  sources = [
+    "scalability_mode.cc",
+    "scalability_mode.h",
+  ]
+  deps = [
+    "../../rtc_base:checks",
+    "../../rtc_base/system:rtc_export",
+  ]
+  absl_deps = [ "//third_party/abseil-cpp/absl/strings" ]
 }
 
 rtc_library("video_codecs_api") {
@@ -144,6 +152,8 @@
     "../../modules/video_coding:webrtc_vp8",
     "../../modules/video_coding:webrtc_vp8_scalability",
   ]
+
+  absl_deps = [ "//third_party/abseil-cpp/absl/container:inlined_vector" ]
 }
 
 rtc_source_set("video_encoder_factory_template_libvpx_vp9_adapter") {
@@ -173,6 +183,7 @@
     "../../modules/video_coding/codecs/av1:libaom_av1_encoder",
     "../../modules/video_coding/svc:scalability_mode_util",
   ]
+  absl_deps = [ "//third_party/abseil-cpp/absl/container:inlined_vector" ]
 }
 
 rtc_library("vp8_temporal_layers_factory") {
diff --git a/api/video_codecs/scalability_mode.cc b/api/video_codecs/scalability_mode.cc
new file mode 100644
index 0000000..7dc8fe3
--- /dev/null
+++ b/api/video_codecs/scalability_mode.cc
@@ -0,0 +1,77 @@
+/*
+ *  Copyright (c) 2022 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "api/video_codecs/scalability_mode.h"
+
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+
+absl::string_view ScalabilityModeToString(ScalabilityMode scalability_mode) {
+  switch (scalability_mode) {
+    case ScalabilityMode::kL1T1:
+      return "L1T1";
+    case ScalabilityMode::kL1T2:
+      return "L1T2";
+    case ScalabilityMode::kL1T2h:
+      return "L1T2h";
+    case ScalabilityMode::kL1T3:
+      return "L1T3";
+    case ScalabilityMode::kL1T3h:
+      return "L1T3h";
+    case ScalabilityMode::kL2T1:
+      return "L2T1";
+    case ScalabilityMode::kL2T1h:
+      return "L2T1h";
+    case ScalabilityMode::kL2T1_KEY:
+      return "L2T1_KEY";
+    case ScalabilityMode::kL2T2:
+      return "L2T2";
+    case ScalabilityMode::kL2T2h:
+      return "L2T2h";
+    case ScalabilityMode::kL2T2_KEY:
+      return "L2T2_KEY";
+    case ScalabilityMode::kL2T2_KEY_SHIFT:
+      return "L2T2_KEY_SHIFT";
+    case ScalabilityMode::kL2T3:
+      return "L2T3";
+    case ScalabilityMode::kL2T3h:
+      return "L2T3h";
+    case ScalabilityMode::kL2T3_KEY:
+      return "L2T3_KEY";
+    case ScalabilityMode::kL3T1:
+      return "L3T1";
+    case ScalabilityMode::kL3T1h:
+      return "L3T1h";
+    case ScalabilityMode::kL3T1_KEY:
+      return "L3T1_KEY";
+    case ScalabilityMode::kL3T2:
+      return "L3T2";
+    case ScalabilityMode::kL3T2h:
+      return "L3T2h";
+    case ScalabilityMode::kL3T2_KEY:
+      return "L3T2_KEY";
+    case ScalabilityMode::kL3T3:
+      return "L3T3";
+    case ScalabilityMode::kL3T3h:
+      return "L3T3h";
+    case ScalabilityMode::kL3T3_KEY:
+      return "L3T3_KEY";
+    case ScalabilityMode::kS2T1:
+      return "S2T1";
+    case ScalabilityMode::kS2T3:
+      return "S2T3";
+    case ScalabilityMode::kS3T3:
+      return "S3T3";
+  }
+  RTC_CHECK_NOTREACHED();
+}
+
+}  // namespace webrtc
diff --git a/api/video_codecs/scalability_mode.h b/api/video_codecs/scalability_mode.h
index a33b9e4..397e3d3 100644
--- a/api/video_codecs/scalability_mode.h
+++ b/api/video_codecs/scalability_mode.h
@@ -11,6 +11,12 @@
 #ifndef API_VIDEO_CODECS_SCALABILITY_MODE_H_
 #define API_VIDEO_CODECS_SCALABILITY_MODE_H_
 
+#include <stddef.h>
+#include <stdint.h>
+
+#include "absl/strings/string_view.h"
+#include "rtc_base/system/rtc_export.h"
+
 namespace webrtc {
 
 // Supported scalability modes. Most applications should use the
@@ -18,7 +24,7 @@
 // This list of currently recognized modes is intended for the api boundary
 // between webrtc and injected encoders. Any application usage outside of
 // injected encoders is strongly discouraged.
-enum class ScalabilityMode {
+enum class ScalabilityMode : uint8_t {
   kL1T1,
   kL1T2,
   kL1T2h,
@@ -48,5 +54,44 @@
   kS3T3,
 };
 
+inline constexpr ScalabilityMode kAllScalabilityModes[] = {
+    // clang-format off
+    ScalabilityMode::kL1T1,
+    ScalabilityMode::kL1T2,
+    ScalabilityMode::kL1T2h,
+    ScalabilityMode::kL1T3,
+    ScalabilityMode::kL1T3h,
+    ScalabilityMode::kL2T1,
+    ScalabilityMode::kL2T1h,
+    ScalabilityMode::kL2T1_KEY,
+    ScalabilityMode::kL2T2,
+    ScalabilityMode::kL2T2h,
+    ScalabilityMode::kL2T2_KEY,
+    ScalabilityMode::kL2T2_KEY_SHIFT,
+    ScalabilityMode::kL2T3,
+    ScalabilityMode::kL2T3h,
+    ScalabilityMode::kL2T3_KEY,
+    ScalabilityMode::kL3T1,
+    ScalabilityMode::kL3T1h,
+    ScalabilityMode::kL3T1_KEY,
+    ScalabilityMode::kL3T2,
+    ScalabilityMode::kL3T2h,
+    ScalabilityMode::kL3T2_KEY,
+    ScalabilityMode::kL3T3,
+    ScalabilityMode::kL3T3h,
+    ScalabilityMode::kL3T3_KEY,
+    ScalabilityMode::kS2T1,
+    ScalabilityMode::kS2T3,
+    ScalabilityMode::kS3T3,
+    // clang-format on
+};
+
+inline constexpr size_t kScalabilityModeCount =
+    sizeof(kAllScalabilityModes) / sizeof(ScalabilityMode);
+
+RTC_EXPORT
+absl::string_view ScalabilityModeToString(ScalabilityMode scalability_mode);
+
 }  // namespace webrtc
+
 #endif  // API_VIDEO_CODECS_SCALABILITY_MODE_H_
diff --git a/api/video_codecs/sdp_video_format.cc b/api/video_codecs/sdp_video_format.cc
index 67c8913..3543806 100644
--- a/api/video_codecs/sdp_video_format.cc
+++ b/api/video_codecs/sdp_video_format.cc
@@ -70,6 +70,15 @@
                                const Parameters& parameters)
     : name(name), parameters(parameters) {}
 
+SdpVideoFormat::SdpVideoFormat(
+    const std::string& name,
+    const Parameters& parameters,
+    const absl::InlinedVector<ScalabilityMode, kScalabilityModeCount>&
+        scalability_modes)
+    : name(name),
+      parameters(parameters),
+      scalability_modes(scalability_modes) {}
+
 SdpVideoFormat::SdpVideoFormat(const SdpVideoFormat&) = default;
 SdpVideoFormat::SdpVideoFormat(SdpVideoFormat&&) = default;
 SdpVideoFormat& SdpVideoFormat::operator=(const SdpVideoFormat&) = default;
@@ -80,9 +89,24 @@
 std::string SdpVideoFormat::ToString() const {
   rtc::StringBuilder builder;
   builder << "Codec name: " << name << ", parameters: {";
-  for (const auto& kv : parameters)
+  for (const auto& kv : parameters) {
     builder << " " << kv.first << "=" << kv.second;
+  }
+
   builder << " }";
+  if (!scalability_modes.empty()) {
+    builder << ", scalability_modes: [";
+    bool first = true;
+    for (const auto scalability_mode : scalability_modes) {
+      if (first) {
+        first = false;
+      } else {
+        builder << ", ";
+      }
+      builder << ScalabilityModeToString(scalability_mode);
+    }
+    builder << "]";
+  }
 
   return builder.str();
 }
@@ -105,7 +129,8 @@
 }
 
 bool operator==(const SdpVideoFormat& a, const SdpVideoFormat& b) {
-  return a.name == b.name && a.parameters == b.parameters;
+  return a.name == b.name && a.parameters == b.parameters &&
+         a.scalability_modes == b.scalability_modes;
 }
 
 }  // namespace webrtc
diff --git a/api/video_codecs/sdp_video_format.h b/api/video_codecs/sdp_video_format.h
index a1e23f4..850632e 100644
--- a/api/video_codecs/sdp_video_format.h
+++ b/api/video_codecs/sdp_video_format.h
@@ -14,7 +14,9 @@
 #include <map>
 #include <string>
 
+#include "absl/container/inlined_vector.h"
 #include "api/array_view.h"
+#include "api/video_codecs/scalability_mode.h"
 #include "rtc_base/system/rtc_export.h"
 
 namespace webrtc {
@@ -26,6 +28,11 @@
 
   explicit SdpVideoFormat(const std::string& name);
   SdpVideoFormat(const std::string& name, const Parameters& parameters);
+  SdpVideoFormat(
+      const std::string& name,
+      const Parameters& parameters,
+      const absl::InlinedVector<ScalabilityMode, kScalabilityModeCount>&
+          scalability_modes);
   SdpVideoFormat(const SdpVideoFormat&);
   SdpVideoFormat(SdpVideoFormat&&);
   SdpVideoFormat& operator=(const SdpVideoFormat&);
@@ -51,6 +58,7 @@
 
   std::string name;
   Parameters parameters;
+  absl::InlinedVector<ScalabilityMode, kScalabilityModeCount> scalability_modes;
 };
 
 }  // namespace webrtc
diff --git a/api/video_codecs/test/video_encoder_factory_template_tests.cc b/api/video_codecs/test/video_encoder_factory_template_tests.cc
index b9dfac9..4c3d0cd 100644
--- a/api/video_codecs/test/video_encoder_factory_template_tests.cc
+++ b/api/video_codecs/test/video_encoder_factory_template_tests.cc
@@ -17,6 +17,7 @@
 #include "test/gmock.h"
 #include "test/gtest.h"
 
+using ::testing::Contains;
 using ::testing::Each;
 using ::testing::Eq;
 using ::testing::Field;
@@ -125,9 +126,12 @@
 
 TEST(VideoEncoderFactoryTemplate, LibvpxVp8) {
   VideoEncoderFactoryTemplate<LibvpxVp8EncoderTemplateAdapter> factory;
-  const SdpVideoFormat kVp8Sdp("VP8");
-  EXPECT_THAT(factory.GetSupportedFormats(), UnorderedElementsAre(kVp8Sdp));
-  EXPECT_THAT(factory.CreateVideoEncoder(kVp8Sdp), Ne(nullptr));
+  auto formats = factory.GetSupportedFormats();
+  EXPECT_THAT(formats.size(), 1);
+  EXPECT_THAT(formats[0], Field(&SdpVideoFormat::name, "VP8"));
+  EXPECT_THAT(formats[0], Field(&SdpVideoFormat::scalability_modes,
+                                Contains(ScalabilityMode::kL1T3)));
+  EXPECT_THAT(factory.CreateVideoEncoder(formats[0]), Ne(nullptr));
 }
 
 TEST(VideoEncoderFactoryTemplate, LibvpxVp9) {
@@ -135,6 +139,8 @@
   auto formats = factory.GetSupportedFormats();
   EXPECT_THAT(formats, Not(IsEmpty()));
   EXPECT_THAT(formats, Each(Field(&SdpVideoFormat::name, "VP9")));
+  EXPECT_THAT(formats, Each(Field(&SdpVideoFormat::scalability_modes,
+                                  Contains(ScalabilityMode::kL3T3_KEY))));
   EXPECT_THAT(factory.CreateVideoEncoder(formats[0]), Ne(nullptr));
 }
 
@@ -146,15 +152,20 @@
   auto formats = factory.GetSupportedFormats();
   EXPECT_THAT(formats, Not(IsEmpty()));
   EXPECT_THAT(formats, Each(Field(&SdpVideoFormat::name, "H264")));
+  EXPECT_THAT(formats, Each(Field(&SdpVideoFormat::scalability_modes,
+                                  Contains(ScalabilityMode::kL1T3))));
   EXPECT_THAT(factory.CreateVideoEncoder(formats[0]), Ne(nullptr));
 }
 #endif  // defined(WEBRTC_USE_H264)
 
 TEST(VideoEncoderFactoryTemplate, LibaomAv1) {
   VideoEncoderFactoryTemplate<LibaomAv1EncoderTemplateAdapter> factory;
-  const SdpVideoFormat kAv1Sdp("AV1");
-  EXPECT_THAT(factory.GetSupportedFormats(), UnorderedElementsAre(kAv1Sdp));
-  EXPECT_THAT(factory.CreateVideoEncoder(kAv1Sdp), Ne(nullptr));
+  auto formats = factory.GetSupportedFormats();
+  EXPECT_THAT(formats.size(), 1);
+  EXPECT_THAT(formats[0], Field(&SdpVideoFormat::name, "AV1"));
+  EXPECT_THAT(formats[0], Field(&SdpVideoFormat::scalability_modes,
+                                Contains(ScalabilityMode::kL3T3_KEY)));
+  EXPECT_THAT(factory.CreateVideoEncoder(formats[0]), Ne(nullptr));
 }
 
 }  // namespace
diff --git a/api/video_codecs/video_encoder_factory_template_libaom_av1_adapter.h b/api/video_codecs/video_encoder_factory_template_libaom_av1_adapter.h
index d71cc00..ce273ff 100644
--- a/api/video_codecs/video_encoder_factory_template_libaom_av1_adapter.h
+++ b/api/video_codecs/video_encoder_factory_template_libaom_av1_adapter.h
@@ -14,13 +14,17 @@
 #include <memory>
 #include <vector>
 
+#include "absl/container/inlined_vector.h"
 #include "modules/video_coding/codecs/av1/av1_svc_config.h"
 #include "modules/video_coding/codecs/av1/libaom_av1_encoder.h"
 
 namespace webrtc {
 struct LibaomAv1EncoderTemplateAdapter {
   static std::vector<SdpVideoFormat> SupportedFormats() {
-    return {SdpVideoFormat("AV1")};
+    absl::InlinedVector<ScalabilityMode, kScalabilityModeCount>
+        scalability_modes = LibaomAv1EncoderSupportedScalabilityModes();
+    return {
+        SdpVideoFormat("AV1", SdpVideoFormat::Parameters(), scalability_modes)};
   }
 
   static std::unique_ptr<VideoEncoder> CreateEncoder(
diff --git a/api/video_codecs/video_encoder_factory_template_libvpx_vp8_adapter.h b/api/video_codecs/video_encoder_factory_template_libvpx_vp8_adapter.h
index c00c6d1..d7d0cd4 100644
--- a/api/video_codecs/video_encoder_factory_template_libvpx_vp8_adapter.h
+++ b/api/video_codecs/video_encoder_factory_template_libvpx_vp8_adapter.h
@@ -14,13 +14,21 @@
 #include <memory>
 #include <vector>
 
+#include "absl/container/inlined_vector.h"
 #include "modules/video_coding/codecs/vp8/include/vp8.h"
 #include "modules/video_coding/codecs/vp8/vp8_scalability.h"
 
 namespace webrtc {
 struct LibvpxVp8EncoderTemplateAdapter {
   static std::vector<SdpVideoFormat> SupportedFormats() {
-    return {SdpVideoFormat("VP8")};
+    absl::InlinedVector<ScalabilityMode, kScalabilityModeCount>
+        scalability_modes;
+    for (const auto scalability_mode : kVP8SupportedScalabilityModes) {
+      scalability_modes.push_back(scalability_mode);
+    }
+
+    return {
+        SdpVideoFormat("VP8", SdpVideoFormat::Parameters(), scalability_modes)};
   }
 
   static std::unique_ptr<VideoEncoder> CreateEncoder(
diff --git a/api/video_codecs/video_encoder_factory_template_libvpx_vp9_adapter.h b/api/video_codecs/video_encoder_factory_template_libvpx_vp9_adapter.h
index 9947ec9..c10fda4 100644
--- a/api/video_codecs/video_encoder_factory_template_libvpx_vp9_adapter.h
+++ b/api/video_codecs/video_encoder_factory_template_libvpx_vp9_adapter.h
@@ -19,7 +19,7 @@
 namespace webrtc {
 struct LibvpxVp9EncoderTemplateAdapter {
   static std::vector<SdpVideoFormat> SupportedFormats() {
-    return SupportedVP9Codecs();
+    return SupportedVP9Codecs(/*add_scalability_modes=*/true);
   }
 
   static std::unique_ptr<VideoEncoder> CreateEncoder(
diff --git a/api/video_codecs/video_encoder_factory_template_open_h264_adapter.h b/api/video_codecs/video_encoder_factory_template_open_h264_adapter.h
index 9959617..5a9742a 100644
--- a/api/video_codecs/video_encoder_factory_template_open_h264_adapter.h
+++ b/api/video_codecs/video_encoder_factory_template_open_h264_adapter.h
@@ -22,7 +22,7 @@
 #if defined(WEBRTC_USE_H264)
 struct OpenH264EncoderTemplateAdapter {
   static std::vector<SdpVideoFormat> SupportedFormats() {
-    return SupportedH264Codecs();
+    return SupportedH264Codecs(/*add_scalability_modes=*/true);
   }
 
   static std::unique_ptr<VideoEncoder> CreateEncoder(