Add field trial and test for NetEq extra delay

Adding field trial WebRTC-Audio-NetEqExtraDelay with a parameter value
to set the extra delay in NetEq. This overrides the
extra_output_delay_ms parameter in NetEq::Config.

Bug: b/156734419
Change-Id: Iae7d439fafa3059494249959ac13a02de63d6b7a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/176858
Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31493}

modules/audio_coding/neteq/neteq_impl.cc

@@ -51,6 +51,7 @@
 #include "rtc_base/strings/audio_format_to_string.h"
 #include "rtc_base/trace_event.h"
 #include "system_wrappers/include/clock.h"
+#include "system_wrappers/include/field_trial.h"
 
 namespace webrtc {
 namespace {
@@ -73,6 +74,24 @@ std::unique_ptr<NetEqController> CreateNetEqController(
   return controller_factory.CreateNetEqController(config);
 }
 
+int GetDelayChainLengthMs(int config_extra_delay_ms) {
+  constexpr char kExtraDelayFieldTrial[] = "WebRTC-Audio-NetEqExtraDelay";
+  if (webrtc::field_trial::IsEnabled(kExtraDelayFieldTrial)) {
+    const auto field_trial_string =
+        webrtc::field_trial::FindFullName(kExtraDelayFieldTrial);
+    int extra_delay_ms = -1;
+    if (sscanf(field_trial_string.c_str(), "Enabled-%d", &extra_delay_ms) ==
+            1 &&
+        extra_delay_ms >= 0 && extra_delay_ms <= 2000) {
+      RTC_LOG(LS_INFO) << "Delay chain length set to " << extra_delay_ms
+                       << " ms in field trial";
+      return (extra_delay_ms / 10) * 10;  // Rounding down to multiple of 10.
+    }
+  }
+  // Field trial not set, or invalid value read. Use value from config.
+  return config_extra_delay_ms;
+}
+
 }  // namespace
 
 NetEqImpl::Dependencies::Dependencies(
@@ -141,9 +160,9 @@ NetEqImpl::NetEqImpl(const NetEq::Config& config,
                                 tick_timer_.get()),
       no_time_stretching_(config.for_test_no_time_stretching),
       enable_rtx_handling_(config.enable_rtx_handling),
-      output_delay_chain_(
+      output_delay_chain_ms_(
-          rtc::CheckedDivExact(config.extra_output_delay_ms, 10)),
+          GetDelayChainLengthMs(config.extra_output_delay_ms)),
-      output_delay_chain_ms_(config.extra_output_delay_ms) {
+      output_delay_chain_(rtc::CheckedDivExact(output_delay_chain_ms_, 10)) {
   RTC_LOG(LS_INFO) << "NetEq config: " << config.ToString();
   int fs = config.sample_rate_hz;
   if (fs != 8000 && fs != 16000 && fs != 32000 && fs != 48000) {

modules/audio_coding/neteq/neteq_impl.h

@@ -403,14 +403,14 @@ class NetEqImpl : public webrtc::NetEq {
   rtc::BufferT<int16_t> concealment_audio_ RTC_GUARDED_BY(crit_sect_);
   const bool enable_rtx_handling_ RTC_GUARDED_BY(crit_sect_);
   // Data members used for adding extra delay to the output of NetEq.
+  // The delay in ms (which is 10 times the number of elements in
+  // output_delay_chain_).
+  const int output_delay_chain_ms_ RTC_GUARDED_BY(crit_sect_);
   // Vector of AudioFrames which contains the delayed audio. Accessed as a
   // circular buffer.
   std::vector<AudioFrame> output_delay_chain_ RTC_GUARDED_BY(crit_sect_);
   // Index into output_delay_chain_.
   size_t output_delay_chain_ix_ RTC_GUARDED_BY(crit_sect_) = 0;
-  // The delay in ms (which is 10 times the number of elements in
-  // output_delay_chain_).
-  const int output_delay_chain_ms_ RTC_GUARDED_BY(crit_sect_);
   // Did output_delay_chain_ get populated yet?
   bool output_delay_chain_empty_ RTC_GUARDED_BY(crit_sect_) = true;
   // Contains the sample rate of the AudioFrame last emitted from the delay

modules/audio_coding/neteq/neteq_unittest.cc

@@ -1253,5 +1253,35 @@ TEST(NetEqOutputDelayTest, RunTest) {
   }
 }
 
+// Tests the extra output delay functionality of NetEq when configured via
+// field trial.
+TEST(NetEqOutputDelayTest, RunTestWithFieldTrial) {
+  test::ScopedFieldTrials field_trial(
+      "WebRTC-Audio-NetEqExtraDelay/Enabled-50/");
+  constexpr int kExpectedDelayMs = 50;
+  std::vector<int16_t> output;
+  const auto result = DelayLineNetEqTest(0, &output);
+
+  // The base delay values are taken from the resuts of the non-delayed case in
+  // NetEqOutputDelayTest.RunTest above.
+  EXPECT_EQ(10 + kExpectedDelayMs, result.target_delay_ms);
+  EXPECT_EQ(24 + kExpectedDelayMs, result.filtered_current_delay_ms);
+}
+
+// Set a non-multiple-of-10 value in the field trial, and verify that we don't
+// crash, and that the result is rounded down.
+TEST(NetEqOutputDelayTest, RunTestWithFieldTrialOddValue) {
+  test::ScopedFieldTrials field_trial(
+      "WebRTC-Audio-NetEqExtraDelay/Enabled-103/");
+  constexpr int kRoundedDelayMs = 100;
+  std::vector<int16_t> output;
+  const auto result = DelayLineNetEqTest(0, &output);
+
+  // The base delay values are taken from the resuts of the non-delayed case in
+  // NetEqOutputDelayTest.RunTest above.
+  EXPECT_EQ(10 + kRoundedDelayMs, result.target_delay_ms);
+  EXPECT_EQ(24 + kRoundedDelayMs, result.filtered_current_delay_ms);
+}
+
 }  // namespace test
 }  // namespace webrtc