Piggybacking simulcast id and ALR experiment id into video content type extension.

webrtc/modules/pacing/alr_detector.cc

Index: webrtc/modules/pacing/alr_detector.cc
diff --git a/webrtc/modules/pacing/alr_detector.cc b/webrtc/modules/pacing/alr_detector.cc
index 993c6cd07edde5b87d2ea5f4b061dc5c183c5a40..194ddbccf83c305e221bae1771c2584b4cf64961 100644
--- a/webrtc/modules/pacing/alr_detector.cc
+++ b/webrtc/modules/pacing/alr_detector.cc
@@ -10,6 +10,7 @@
 
 #include "webrtc/modules/pacing/alr_detector.h"
 
+#include <map>
 #include <string>
 
 #include "webrtc/rtc_base/checks.h"
@@ -81,6 +82,16 @@ AlrDetector::ParseAlrSettingsFromFieldTrial(const char* experiment_name) {
   rtc::Optional<AlrExperimentSettings> ret;
   std::string group_name = field_trial::FindFullName(experiment_name);
 
+  static std::map<const char*,
+                  rtc::Optional<AlrDetector::AlrExperimentSettings>>
+      computed_results;
+
+  auto it = computed_results.find(experiment_name);
+  if (it != computed_results.end()) {
+    return it->second;
+  }
+  computed_results[experiment_name] = ret;

[sprang_webrtc, 2017/08/24 09:13:16]

Looks like you can drop this insertion?

[ilnik, 2017/08/25 12:35:07]

No. Currently the function may exit below if it fails to parse a string.
In that case map will already contain correct empty value. Future calls will
never attempt to parse the string again.

If this insertion is removed, incorrect strings will be parsed on each call.

+
   const std::string kIgnoredSuffix = "_Dogfood";
   if (group_name.rfind(kIgnoredSuffix) ==
       group_name.length() - kIgnoredSuffix.length()) {
@@ -91,11 +102,12 @@ AlrDetector::ParseAlrSettingsFromFieldTrial(const char* experiment_name) {
     return ret;
 
   AlrExperimentSettings settings;
-  if (sscanf(group_name.c_str(), "%f,%" PRId64 ",%d,%d,%d",
+  if (sscanf(group_name.c_str(), "%f,%" PRId64 ",%d,%d,%d,%d",
              &settings.pacing_factor, &settings.max_paced_queue_time,
              &settings.alr_bandwidth_usage_percent,
              &settings.alr_start_budget_level_percent,
-             &settings.alr_stop_budget_level_percent) == 5) {
+             &settings.alr_stop_budget_level_percent,
+             &settings.group_id) == 6) {
     ret.emplace(settings);
     LOG(LS_INFO) << "Using ALR experiment settings: "
                     "pacing factor: "
@@ -106,11 +118,13 @@ AlrDetector::ParseAlrSettingsFromFieldTrial(const char* experiment_name) {
                  << ", ALR end budget level percent: "
                  << settings.alr_start_budget_level_percent
                  << ", ALR end budget level percent: "
-                 << settings.alr_stop_budget_level_percent;
+                 << settings.alr_stop_budget_level_percent
+                 << ", ALR experiment group ID: " << settings.group_id;
   } else {
     LOG(LS_INFO) << "Failed to parse ALR experiment: " << experiment_name;
   }
 
+  computed_results[experiment_name] = ret;
   return ret;
 }