Added experiment to improve handling of frame length changes in NetEq.

The field trial effects two things: after a frame length change the IAT
histogram is scaled to prevent an immediate change in target buffer
level. Also, the peak history in the delay peak detector is cleared, 
because the size of the peaks is stored in number of packets (which
will be incorrect after a frame length change).

Bug: webrtc:8381
Change-Id: I214b990f6e5959b655b6542884a7f75da181a0d8
Reviewed-on: https://webrtc-review.googlesource.com/8101
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Commit-Queue: Ivo Creusen <ivoc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20284}

modules/audio_coding/BUILD.gn

@@ -1143,14 +1143,10 @@ rtc_source_set("neteq_tools") {
   sources = [
     "neteq/tools/fake_decode_from_file.cc",
     "neteq/tools/fake_decode_from_file.h",
-    "neteq/tools/input_audio_file.cc",
-    "neteq/tools/input_audio_file.h",
     "neteq/tools/neteq_delay_analyzer.cc",
     "neteq/tools/neteq_delay_analyzer.h",
     "neteq/tools/neteq_replacement_input.cc",
     "neteq/tools/neteq_replacement_input.h",
-    "neteq/tools/resample_input_audio_file.cc",
-    "neteq/tools/resample_input_audio_file.h",
   ]
 
   public_configs = [ ":neteq_tools_config" ]
@@ -1165,16 +1161,31 @@ rtc_source_set("neteq_tools") {
     "../../api:array_view",
     "../../api:optional",
     "../../api/audio_codecs:audio_codecs_api",
-    "../../common_audio",
     "../../rtc_base:rtc_base_approved",
     "../rtp_rtcp",
   ]
 
   public_deps = [
+    ":neteq_input_audio_tools",
     ":neteq_tools_minimal",
   ]
 }
 
+rtc_source_set("neteq_input_audio_tools") {
+  sources = [
+    "neteq/tools/input_audio_file.cc",
+    "neteq/tools/input_audio_file.h",
+    "neteq/tools/resample_input_audio_file.cc",
+    "neteq/tools/resample_input_audio_file.h",
+  ]
+
+  deps = [
+    "../..:webrtc_common",
+    "../../common_audio",
+    "../../rtc_base:rtc_base_approved",
+  ]
+}
+
 if (rtc_enable_protobuf) {
   rtc_static_library("rtc_event_log_source") {
     testonly = true

modules/audio_coding/neteq/delay_manager.cc

@@ -14,12 +14,14 @@
 #include <math.h>
 
 #include <algorithm>  // max, min
+#include <numeric>
 
 #include "common_audio/signal_processing/include/signal_processing_library.h"
 #include "modules/audio_coding/neteq/delay_peak_detector.h"
 #include "modules/include/module_common_types.h"
 #include "rtc_base/logging.h"
 #include "rtc_base/safe_conversions.h"
+#include "system_wrappers/include/field_trial.h"
 
 namespace webrtc {
 
@@ -43,7 +45,9 @@ DelayManager::DelayManager(size_t max_packets_in_buffer,
       iat_cumulative_sum_(0),
       max_iat_cumulative_sum_(0),
       peak_detector_(*peak_detector),
-      last_pack_cng_or_dtmf_(1) {
+      last_pack_cng_or_dtmf_(1),
+      frame_length_change_experiment_(
+          field_trial::IsEnabled("WebRTC-Audio-NetEqFramelengthExperiment")) {
   assert(peak_detector);  // Should never be NULL.
   Reset();
 }
@@ -298,6 +302,10 @@ int DelayManager::SetPacketAudioLength(int length_ms) {
     LOG_F(LS_ERROR) << "length_ms = " << length_ms;
     return -1;
   }
+  if (frame_length_change_experiment_ && packet_len_ms_ != length_ms) {
+    iat_vector_ = ScaleHistogram(iat_vector_, packet_len_ms_, length_ms);
+  }
+
   packet_len_ms_ = length_ms;
   peak_detector_.SetPacketAudioLength(packet_len_ms_);
   packet_iat_stopwatch_ = tick_timer_->GetNewStopwatch();
@@ -378,6 +386,41 @@ void DelayManager::RegisterEmptyPacket() {
   ++last_seq_no_;
 }
 
+DelayManager::IATVector DelayManager::ScaleHistogram(const IATVector& histogram,
+                                                     int old_packet_length,
+                                                     int new_packet_length) {
+  RTC_DCHECK_GT(new_packet_length, 0);
+  RTC_DCHECK_EQ(old_packet_length % 10, 0);
+  RTC_DCHECK_EQ(new_packet_length % 10, 0);
+  IATVector new_histogram(histogram.size(), 0);
+  int acc = 0;
+  int time_counter = 0;
+  size_t new_histogram_idx = 0;
+  for (size_t i = 0; i < histogram.size(); i++) {
+    acc += histogram[i];
+    time_counter += old_packet_length;
+    // The bins should be scaled, to ensure the histogram still sums to one.
+    const int scaled_acc = acc * new_packet_length / time_counter;
+    int actually_used_acc = 0;
+    while (time_counter >= new_packet_length) {
+      actually_used_acc += scaled_acc;
+      new_histogram[new_histogram_idx] += scaled_acc;
+      new_histogram_idx =
+          std::min(new_histogram_idx + 1, new_histogram.size() - 1);
+      time_counter -= new_packet_length;
+    }
+    // Only subtract the part that was succesfully written to the new histogram.
+    acc -= actually_used_acc;
+  }
+  // If there is anything left in acc (due to rounding errors), add it to the
+  // last bin.
+  new_histogram[new_histogram_idx] += acc;
+  RTC_DCHECK_EQ(histogram.size(), new_histogram.size());
+  RTC_DCHECK_EQ(accumulate(histogram.begin(), histogram.end(), 0),
+                accumulate(new_histogram.begin(), new_histogram.end(), 0));
+  return new_histogram;
+}
+
 bool DelayManager::SetMinimumDelay(int delay_ms) {
   // Minimum delay shouldn't be more than maximum delay, if any maximum is set.
   // Also, if possible check |delay| to less than 75% of

modules/audio_coding/neteq/delay_manager.h

@@ -100,6 +100,13 @@ class DelayManager {
   // packet will shift the sequence numbers for the following packets.
   virtual void RegisterEmptyPacket();
 
+  // Apply compression or stretching to the IAT histogram, for a change in frame
+  // size. This returns an updated histogram. This function is public for
+  // testability.
+  static IATVector ScaleHistogram(const IATVector& histogram,
+                                  int old_packet_length,
+                                  int new_packet_length);
+
   // Accessors and mutators.
   // Assuming |delay| is in valid range.
   virtual bool SetMinimumDelay(int delay_ms);
@@ -166,6 +173,7 @@ class DelayManager {
   std::unique_ptr<TickTimer::Stopwatch> max_iat_stopwatch_;
   DelayPeakDetector& peak_detector_;
   int last_pack_cng_or_dtmf_;
+  const bool frame_length_change_experiment_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(DelayManager);
 };

modules/audio_coding/neteq/delay_manager_unittest.cc

@@ -335,4 +335,80 @@ TEST_F(DelayManagerTest, Failures) {
   EXPECT_FALSE(dm_->SetMaximumDelay(60));
 }
 
+// Test if the histogram is stretched correctly if the packet size is decreased.
+TEST(DelayManagerIATScalingTest, StretchTest) {
+  using IATVector = DelayManager::IATVector;
+  // Test a straightforward 60ms to 20ms change.
+  IATVector iat = {12, 0, 0, 0, 0, 0};
+  IATVector expected_result = {4, 4, 4, 0, 0, 0};
+  IATVector stretched_iat = DelayManager::ScaleHistogram(iat, 60, 20);
+  EXPECT_EQ(stretched_iat, expected_result);
+
+  // Test an example where the last bin in the stretched histogram should
+  // contain the sum of the elements that don't fit into the new histogram.
+  iat = {18, 15, 12, 9, 6, 3, 0};
+  expected_result = {6, 6, 6, 5, 5, 5, 30};
+  stretched_iat = DelayManager::ScaleHistogram(iat, 60, 20);
+  EXPECT_EQ(stretched_iat, expected_result);
+
+  // Test a 120ms to 60ms change.
+  iat = {18, 16, 14, 4, 0};
+  expected_result = {9, 9, 8, 8, 18};
+  stretched_iat = DelayManager::ScaleHistogram(iat, 120, 60);
+  EXPECT_EQ(stretched_iat, expected_result);
+
+  // Test a 120ms to 20ms change.
+  iat = {19, 12, 0, 0, 0, 0, 0, 0};
+  expected_result = {3, 3, 3, 3, 3, 3, 2, 11};
+  stretched_iat = DelayManager::ScaleHistogram(iat, 120, 20);
+  EXPECT_EQ(stretched_iat, expected_result);
+
+  // Test a 70ms to 40ms change.
+  iat = {13, 7, 5, 3, 1, 5, 12, 11, 3, 0, 0, 0};
+  expected_result = {7, 5, 5, 3, 3, 2, 2, 1, 2, 2, 6, 22};
+  stretched_iat = DelayManager::ScaleHistogram(iat, 70, 40);
+  EXPECT_EQ(stretched_iat, expected_result);
+
+  // Test a 30ms to 20ms change.
+  iat = {13, 7, 5, 3, 1, 5, 12, 11, 3, 0, 0, 0};
+  expected_result = {8, 6, 6, 3, 2, 2, 1, 3, 3, 8, 7, 11};
+  stretched_iat = DelayManager::ScaleHistogram(iat, 30, 20);
+  EXPECT_EQ(stretched_iat, expected_result);
+}
+
+// Test if the histogram is compressed correctly if the packet size is
+// increased.
+TEST(DelayManagerIATScalingTest, CompressionTest) {
+  using IATVector = DelayManager::IATVector;
+  // Test a 20 to 60 ms change.
+  IATVector iat = {12, 11, 10, 3, 2, 1};
+  IATVector expected_result = {33, 6, 0, 0, 0, 0};
+  IATVector compressed_iat = DelayManager::ScaleHistogram(iat, 20, 60);
+  EXPECT_EQ(compressed_iat, expected_result);
+
+  // Test a 60ms to 120ms change.
+  iat = {18, 16, 14, 4, 1};
+  expected_result = {34, 18, 1, 0, 0};
+  compressed_iat = DelayManager::ScaleHistogram(iat, 60, 120);
+  EXPECT_EQ(compressed_iat, expected_result);
+
+  // Test a 20ms to 120ms change.
+  iat = {18, 12, 5, 4, 4, 3, 5, 1};
+  expected_result = {46, 6, 0, 0, 0, 0, 0, 0};
+  compressed_iat = DelayManager::ScaleHistogram(iat, 20, 120);
+  EXPECT_EQ(compressed_iat, expected_result);
+
+  // Test a 70ms to 80ms change.
+  iat = {13, 7, 5, 3, 1, 5, 12, 11, 3};
+  expected_result = {11, 8, 6, 2, 5, 12, 13, 3, 0};
+  compressed_iat = DelayManager::ScaleHistogram(iat, 70, 80);
+  EXPECT_EQ(compressed_iat, expected_result);
+
+  // Test a 50ms to 110ms change.
+  iat = {13, 7, 5, 3, 1, 5, 12, 11, 3};
+  expected_result = {18, 8, 16, 16, 2, 0, 0, 0, 0};
+  compressed_iat = DelayManager::ScaleHistogram(iat, 50, 110);
+  EXPECT_EQ(compressed_iat, expected_result);
+}
+
 }  // namespace webrtc

modules/audio_coding/neteq/delay_peak_detector.cc

@@ -14,6 +14,7 @@
 
 #include "rtc_base/checks.h"
 #include "rtc_base/safe_conversions.h"
+#include "system_wrappers/include/field_trial.h"
 
 namespace webrtc {
 
@@ -29,7 +30,9 @@ DelayPeakDetector::~DelayPeakDetector() = default;
 DelayPeakDetector::DelayPeakDetector(const TickTimer* tick_timer)
     : peak_found_(false),
       peak_detection_threshold_(0),
-      tick_timer_(tick_timer) {
+      tick_timer_(tick_timer),
+      frame_length_change_experiment_(
+          field_trial::IsEnabled("WebRTC-Audio-NetEqFramelengthExperiment")) {
   RTC_DCHECK(!peak_period_stopwatch_);
 }
 
@@ -42,8 +45,15 @@ void DelayPeakDetector::Reset() {
 // Calculates the threshold in number of packets.
 void DelayPeakDetector::SetPacketAudioLength(int length_ms) {
   if (length_ms > 0) {
+    if (frame_length_change_experiment_) {
+      peak_detection_threshold_ = std::max(2, kPeakHeightMs / length_ms);
+    } else {
       peak_detection_threshold_ = kPeakHeightMs / length_ms;
     }
+  }
+  if (frame_length_change_experiment_) {
+    peak_history_.clear();
+  }
 }
 
 bool DelayPeakDetector::peak_found() {

modules/audio_coding/neteq/delay_peak_detector.h

@@ -66,6 +66,7 @@ class DelayPeakDetector {
   int peak_detection_threshold_;
   const TickTimer* tick_timer_;
   std::unique_ptr<TickTimer::Stopwatch> peak_period_stopwatch_;
+  const bool frame_length_change_experiment_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(DelayPeakDetector);
 };

modules/audio_processing/BUILD.gn

@@ -563,7 +563,7 @@ if (rtc_include_tests) {
       "../../rtc_base:rtc_base_approved",
       "../../system_wrappers:system_wrappers",
       "../../test:test_support",
-      "../audio_coding:neteq_tools",
+      "../audio_coding:neteq_input_audio_tools",
       "aec_dump:mock_aec_dump_unittests",
       "test/conversational_speech:unittest",
       "//testing/gmock",
@@ -802,7 +802,7 @@ if (rtc_include_tests) {
       "../../rtc_base:rtc_base_approved",
       "../../system_wrappers:system_wrappers",
       "../../test:test_support",
-      "../audio_coding:neteq_tools",
+      "../audio_coding:neteq_input_audio_tools",
       "//testing/gtest",
     ]
   }