Prevent Opus DTX from generating intermittent noise during silence

webrtc/modules/audio_coding/codecs/opus/opus_unittest.cc

Index: webrtc/modules/audio_coding/codecs/opus/opus_unittest.cc
diff --git a/webrtc/modules/audio_coding/codecs/opus/opus_unittest.cc b/webrtc/modules/audio_coding/codecs/opus/opus_unittest.cc
index db622a7c7f878381468b48293305f515f88cc597..55b84e90fdd96e97eab7494d5dbb0d4e78e0ea71 100644
--- a/webrtc/modules/audio_coding/codecs/opus/opus_unittest.cc
+++ b/webrtc/modules/audio_coding/codecs/opus/opus_unittest.cc
@@ -53,6 +53,10 @@ class OpusTest : public TestWithParam<::testing::tuple<int, int>> {
   void SetMaxPlaybackRate(WebRtcOpusEncInst* encoder,
                           opus_int32 expect, int32_t set);
 
+  // Verify that all samples in |audio| are bounded in [-|bound|, |bound|].
+  void CheckAudioBounded(int16_t* audio, size_t samples, int channels,
+                         uint16_t bound);
+
   WebRtcOpusEncInst* opus_encoder_;
   WebRtcOpusDecInst* opus_decoder_;
 
@@ -95,6 +99,16 @@ void OpusTest::SetMaxPlaybackRate(WebRtcOpusEncInst* encoder,
   EXPECT_EQ(expect, bandwidth);
 }
 
+void OpusTest::CheckAudioBounded(int16_t* audio, size_t samples, int channels,
+                                 uint16_t bound) {
+  for (size_t i = 0; i < samples; ++i) {
+    for (int c = 0; c < channels; ++c, ++audio) {
+      EXPECT_GE(*audio, -bound);
+      EXPECT_LE(*audio, bound);
+    }
+  }
+}
+
 int OpusTest::EncodeDecode(WebRtcOpusEncInst* encoder,
                            const int16_t* input_audio,
                            size_t input_samples,
@@ -177,9 +191,16 @@ void OpusTest::TestDtxEffect(bool dtx) {
 
   // When Opus is in DTX, it wakes up in a regular basis. It sends two packets,
   // one with an arbitrary size and the other of 1-byte, then stops sending for
-  // 19 frames.
-  const int cycles = 5;
-  for (int j = 0; j < cycles; ++j) {
+  // 19 frames. We run 10 second of pure silence, which is about 25 cycles
+  // (420 ms/cycle).
+  const int kCycles = 24;
+
+  // We check that, after a certain cycles (given that the CNG in Opus needs
+  // time to adapt), the values of DTX decoded signal are bounded by [-1, 1].
+  const int kOutputValueCheckCycle = 18;
+  const uint16_t kOutputValueBound = 1;
+
+  for (int j = 0; j < kCycles; ++j) {
     // DTX mode is maintained 19 frames.
     for (int i = 0; i < 19; ++i) {
       EXPECT_EQ(kOpus20msFrameSamples,
@@ -192,6 +213,10 @@ void OpusTest::TestDtxEffect(bool dtx) {
         EXPECT_EQ(1, opus_encoder_->in_dtx_mode);
         EXPECT_EQ(1, opus_decoder_->in_dtx_mode);
         EXPECT_EQ(2, audio_type);  // Comfort noise.
+        if (j >= kOutputValueCheckCycle) {
+          CheckAudioBounded(output_data_decode, kOpus20msFrameSamples,
+                            channels_, kOutputValueBound);
+        }
       } else {
         EXPECT_GT(encoded_bytes_, 1U);
         EXPECT_EQ(0, opus_encoder_->in_dtx_mode);
@@ -221,6 +246,10 @@ void OpusTest::TestDtxEffect(bool dtx) {
       EXPECT_EQ(1, opus_encoder_->in_dtx_mode);
       EXPECT_EQ(1, opus_decoder_->in_dtx_mode);
       EXPECT_EQ(2, audio_type);  // Comfort noise.
+      if (j >= kOutputValueCheckCycle) {
+        CheckAudioBounded(output_data_decode, kOpus20msFrameSamples,
+                          channels_, kOutputValueBound);
+      }
     } else {
       EXPECT_GT(encoded_bytes_, 1U);
       EXPECT_EQ(0, opus_encoder_->in_dtx_mode);