diff --git a/modules/audio_coding/codecs/opus/interface/opus_interface.h b/modules/audio_coding/codecs/opus/interface/opus_interface.h
index 38ff00d..d788af7 100644
--- a/modules/audio_coding/codecs/opus/interface/opus_interface.h
+++ b/modules/audio_coding/codecs/opus/interface/opus_interface.h
@@ -39,7 +39,7 @@
  * Output:
  *      - encoded               : Output compressed data buffer
  *
- * Return value                 : >0 - Length (in bytes) of coded data
+ * Return value                 : >=0 - Length (in bytes) of coded data
  *                                -1 - Error
  */
 int16_t WebRtcOpus_Encode(OpusEncInst* inst,
@@ -130,6 +130,32 @@
  */
 int16_t WebRtcOpus_DisableFec(OpusEncInst* inst);
 
+/****************************************************************************
+ * WebRtcOpus_EnableDtx()
+ *
+ * This function enables Opus internal DTX for encoding.
+ *
+ * Input:
+ *      - inst               : Encoder context
+ *
+ * Return value              :  0 - Success
+ *                             -1 - Error
+ */
+int16_t WebRtcOpus_EnableDtx(OpusEncInst* inst);
+
+/****************************************************************************
+ * WebRtcOpus_DisableDtx()
+ *
+ * This function disables Opus internal DTX for encoding.
+ *
+ * Input:
+ *      - inst               : Encoder context
+ *
+ * Return value              :  0 - Success
+ *                             -1 - Error
+ */
+int16_t WebRtcOpus_DisableDtx(OpusEncInst* inst);
+
 /*
  * WebRtcOpus_SetComplexity(...)
  *
diff --git a/modules/audio_coding/codecs/opus/opus_inst.h b/modules/audio_coding/codecs/opus/opus_inst.h
index 4597ab8..373db39 100644
--- a/modules/audio_coding/codecs/opus/opus_inst.h
+++ b/modules/audio_coding/codecs/opus/opus_inst.h
@@ -15,12 +15,14 @@
 
 struct WebRtcOpusEncInst {
   OpusEncoder* encoder;
+  int in_dtx_mode;
 };
 
 struct WebRtcOpusDecInst {
   OpusDecoder* decoder;
   int prev_decoded_samples;
   int channels;
+  int in_dtx_mode;
 };
 
 
diff --git a/modules/audio_coding/codecs/opus/opus_interface.c b/modules/audio_coding/codecs/opus/opus_interface.c
index ba7fe13..1b99864 100644
--- a/modules/audio_coding/codecs/opus/opus_interface.c
+++ b/modules/audio_coding/codecs/opus/opus_interface.c
@@ -43,6 +43,7 @@
 
       state->encoder = opus_encoder_create(48000, channels, application,
                                            &error);
+      state->in_dtx_mode = 0;
       if (error == OPUS_OK && state->encoder != NULL) {
         *inst = state;
         return 0;
@@ -80,9 +81,21 @@
                     encoded,
                     length_encoded_buffer);
 
-  if (res > 0) {
+  if (res == 1) {
+    // Indicates DTX since the packet has nothing but a header. In principle,
+    // there is no need to send this packet. However, we do transmit the first
+    // occurrence to let the decoder know that the encoder enters DTX mode.
+    if (inst->in_dtx_mode) {
+      return 0;
+    } else {
+      inst->in_dtx_mode = 1;
+      return 1;
+    }
+  } else if (res > 1) {
+    inst->in_dtx_mode = 0;
     return res;
   }
+
   return -1;
 }
 
@@ -140,6 +153,22 @@
   }
 }
 
+int16_t WebRtcOpus_EnableDtx(OpusEncInst* inst) {
+  if (inst) {
+    return opus_encoder_ctl(inst->encoder, OPUS_SET_DTX(1));
+  } else {
+    return -1;
+  }
+}
+
+int16_t WebRtcOpus_DisableDtx(OpusEncInst* inst) {
+  if (inst) {
+    return opus_encoder_ctl(inst->encoder, OPUS_SET_DTX(0));
+  } else {
+    return -1;
+  }
+}
+
 int16_t WebRtcOpus_SetComplexity(OpusEncInst* inst, int32_t complexity) {
   if (inst) {
     return opus_encoder_ctl(inst->encoder, OPUS_SET_COMPLEXITY(complexity));
@@ -165,6 +194,7 @@
       /* Creation of memory all ok. */
       state->channels = channels;
       state->prev_decoded_samples = kWebRtcOpusDefaultFrameSize;
+      state->in_dtx_mode = 0;
       *inst = state;
       return 0;
     }
@@ -195,53 +225,61 @@
 int16_t WebRtcOpus_DecoderInit(OpusDecInst* inst) {
   int error = opus_decoder_ctl(inst->decoder, OPUS_RESET_STATE);
   if (error == OPUS_OK) {
+    inst->in_dtx_mode = 0;
     return 0;
   }
   return -1;
 }
 
+/* For decoder to determine if it is to output speech or comfort noise. */
+static int16_t DetermineAudioType(OpusDecInst* inst, int16_t encoded_bytes) {
+  // Audio type becomes comfort noise if |encoded_byte| is 1 and keeps
+  // to be so if the following |encoded_byte| are 0 or 1.
+  if (encoded_bytes == 0 && inst->in_dtx_mode) {
+    return 2;  // Comfort noise.
+  } else if (encoded_bytes == 1) {
+    inst->in_dtx_mode = 1;
+    return 2;  // Comfort noise.
+  } else {
+    inst->in_dtx_mode = 0;
+    return 0;  // Speech.
+  }
+}
+
 /* |frame_size| is set to maximum Opus frame size in the normal case, and
  * is set to the number of samples needed for PLC in case of losses.
  * It is up to the caller to make sure the value is correct. */
-static int DecodeNative(OpusDecoder* inst, const uint8_t* encoded,
+static int DecodeNative(OpusDecInst* inst, const uint8_t* encoded,
                         int16_t encoded_bytes, int frame_size,
-                        int16_t* decoded, int16_t* audio_type) {
-  int res = opus_decode(
-      inst, encoded, encoded_bytes, (opus_int16*)decoded, frame_size, 0);
+                        int16_t* decoded, int16_t* audio_type, int decode_fec) {
+  int res = opus_decode(inst->decoder, encoded, encoded_bytes,
+                        (opus_int16*)decoded, frame_size, decode_fec);
 
-  /* TODO(tlegrand): set to DTX for zero-length packets? */
-  *audio_type = 0;
+  if (res <= 0)
+    return -1;
 
-  if (res > 0) {
-    return res;
-  }
-  return -1;
-}
+  *audio_type = DetermineAudioType(inst, encoded_bytes);
 
-static int DecodeFec(OpusDecoder* inst, const uint8_t* encoded,
-                     int16_t encoded_bytes, int frame_size,
-                     int16_t* decoded, int16_t* audio_type) {
-  int res = opus_decode(
-      inst, encoded, encoded_bytes, (opus_int16*)decoded, frame_size, 1);
-
-  /* TODO(tlegrand): set to DTX for zero-length packets? */
-  *audio_type = 0;
-
-  if (res > 0) {
-    return res;
-  }
-  return -1;
+  return res;
 }
 
 int16_t WebRtcOpus_Decode(OpusDecInst* inst, const uint8_t* encoded,
                           int16_t encoded_bytes, int16_t* decoded,
                           int16_t* audio_type) {
-  int decoded_samples = DecodeNative(inst->decoder,
-                                     encoded,
-                                     encoded_bytes,
-                                     kWebRtcOpusMaxFrameSizePerChannel,
-                                     decoded,
-                                     audio_type);
+  int decoded_samples;
+
+  if (encoded_bytes == 0) {
+    *audio_type = DetermineAudioType(inst, encoded_bytes);
+    decoded_samples = WebRtcOpus_DecodePlc(inst, decoded, 1);
+  } else {
+    decoded_samples = DecodeNative(inst,
+                                   encoded,
+                                   encoded_bytes,
+                                   kWebRtcOpusMaxFrameSizePerChannel,
+                                   decoded,
+                                   audio_type,
+                                   0);
+  }
   if (decoded_samples < 0) {
     return -1;
   }
@@ -264,8 +302,8 @@
   plc_samples = number_of_lost_frames * inst->prev_decoded_samples;
   plc_samples = (plc_samples <= kWebRtcOpusMaxFrameSizePerChannel) ?
       plc_samples : kWebRtcOpusMaxFrameSizePerChannel;
-  decoded_samples = DecodeNative(inst->decoder, NULL, 0, plc_samples,
-                                 decoded, &audio_type);
+  decoded_samples = DecodeNative(inst, NULL, 0, plc_samples,
+                                 decoded, &audio_type, 0);
   if (decoded_samples < 0) {
     return -1;
   }
@@ -285,8 +323,8 @@
 
   fec_samples = opus_packet_get_samples_per_frame(encoded, 48000);
 
-  decoded_samples = DecodeFec(inst->decoder, encoded, encoded_bytes,
-                              fec_samples, decoded, audio_type);
+  decoded_samples = DecodeNative(inst, encoded, encoded_bytes,
+                                 fec_samples, decoded, audio_type, 1);
   if (decoded_samples < 0) {
     return -1;
   }
diff --git a/modules/audio_coding/codecs/opus/opus_unittest.cc b/modules/audio_coding/codecs/opus/opus_unittest.cc
index 9c34f51..433bbbc 100644
--- a/modules/audio_coding/codecs/opus/opus_unittest.cc
+++ b/modules/audio_coding/codecs/opus/opus_unittest.cc
@@ -12,34 +12,50 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "webrtc/modules/audio_coding/codecs/opus/interface/opus_interface.h"
 #include "webrtc/modules/audio_coding/codecs/opus/opus_inst.h"
+#include "webrtc/modules/audio_coding/neteq/tools/audio_loop.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
 
-// Number of samples in a 60 ms stereo frame, sampled at 48 kHz.
-const int kOpusMaxFrameSamples = 48 * 60 * 2;
+using test::AudioLoop;
+
 // Maximum number of bytes in output bitstream.
 const size_t kMaxBytes = 1000;
+// Sample rate of Opus.
+const int kOpusRateKhz = 48;
 // Number of samples-per-channel in a 20 ms frame, sampled at 48 kHz.
-const int kOpus20msFrameSamples = 48 * 20;
+const int kOpus20msFrameSamples = kOpusRateKhz * 20;
 // Number of samples-per-channel in a 10 ms frame, sampled at 48 kHz.
-const int kOpus10msFrameSamples = 48 * 10;
+const int kOpus10msFrameSamples = kOpusRateKhz * 10;
 
 class OpusTest : public ::testing::Test {
  protected:
   OpusTest();
-  virtual void SetUp();
 
   void TestSetMaxPlaybackRate(opus_int32 expect, int32_t set);
+  void TestDtxEffect(bool dtx);
+
+  // Prepare |speech_data_| for encoding, read from a hard-coded file.
+  // After preparation, |speech_data_.GetNextBlock()| returns a pointer to a
+  // block of |block_length_ms| milliseconds. The data is looped every
+  // |loop_length_ms| milliseconds.
+  void PrepareSpeechData(int channel, int block_length_ms, int loop_length_ms);
+
+  int EncodeDecode(WebRtcOpusEncInst* encoder,
+                   const int16_t* input_audio,
+                   const int input_samples,
+                   WebRtcOpusDecInst* decoder,
+                   int16_t* output_audio,
+                   int16_t* audio_type);
 
   WebRtcOpusEncInst* opus_mono_encoder_;
   WebRtcOpusEncInst* opus_stereo_encoder_;
   WebRtcOpusDecInst* opus_mono_decoder_;
   WebRtcOpusDecInst* opus_stereo_decoder_;
 
-  int16_t speech_data_[kOpusMaxFrameSamples];
-  int16_t output_data_[kOpusMaxFrameSamples];
+  AudioLoop speech_data_;
   uint8_t bitstream_[kMaxBytes];
+  int encoded_bytes_;
 };
 
 OpusTest::OpusTest()
@@ -49,17 +65,16 @@
       opus_stereo_decoder_(NULL) {
 }
 
-void OpusTest::SetUp() {
-  FILE* input_file;
+void OpusTest::PrepareSpeechData(int channel, int block_length_ms,
+                                 int loop_length_ms) {
   const std::string file_name =
         webrtc::test::ResourcePath("audio_coding/speech_mono_32_48kHz", "pcm");
-  input_file = fopen(file_name.c_str(), "rb");
-  ASSERT_TRUE(input_file != NULL);
-  ASSERT_EQ(kOpusMaxFrameSamples,
-            static_cast<int32_t>(fread(speech_data_, sizeof(int16_t),
-                                       kOpusMaxFrameSamples, input_file)));
-  fclose(input_file);
-  input_file = NULL;
+  if (loop_length_ms < block_length_ms) {
+    loop_length_ms = block_length_ms;
+  }
+  EXPECT_TRUE(speech_data_.Init(file_name,
+                                loop_length_ms * kOpusRateKhz * channel,
+                                block_length_ms * kOpusRateKhz * channel));
 }
 
 void OpusTest::TestSetMaxPlaybackRate(opus_int32 expect, int32_t set) {
@@ -76,6 +91,155 @@
   EXPECT_EQ(expect, bandwidth);
 }
 
+int OpusTest::EncodeDecode(WebRtcOpusEncInst* encoder,
+                           const int16_t* input_audio,
+                           const int input_samples,
+                           WebRtcOpusDecInst* decoder,
+                           int16_t* output_audio,
+                           int16_t* audio_type) {
+  encoded_bytes_ = WebRtcOpus_Encode(encoder,
+                                    input_audio,
+                                    input_samples, kMaxBytes,
+                                    bitstream_);
+  return WebRtcOpus_Decode(decoder, bitstream_,
+                           encoded_bytes_, output_audio,
+                           audio_type);
+}
+
+// Test if encoder/decoder can enter DTX mode properly and do not enter DTX when
+// they should not. This test is signal dependent.
+void OpusTest::TestDtxEffect(bool dtx) {
+  PrepareSpeechData(1, 20, 2000);
+
+  // Create encoder memory.
+  EXPECT_EQ(0, WebRtcOpus_EncoderCreate(&opus_mono_encoder_, 1));
+  EXPECT_EQ(0, WebRtcOpus_DecoderCreate(&opus_mono_decoder_, 1));
+
+  // Set bitrate.
+  EXPECT_EQ(0, WebRtcOpus_SetBitRate(opus_mono_encoder_, 32000));
+
+  // Set input audio as silence.
+  int16_t silence[kOpus20msFrameSamples] = {0};
+
+  // Setting DTX.
+  EXPECT_EQ(0, dtx ? WebRtcOpus_EnableDtx(opus_mono_encoder_) :
+      WebRtcOpus_DisableDtx(opus_mono_encoder_));
+
+  int16_t audio_type;
+  int16_t output_data_decode[kOpus20msFrameSamples];
+
+  for (int i = 0; i < 100; ++i) {
+    EXPECT_EQ(kOpus20msFrameSamples,
+              EncodeDecode(opus_mono_encoder_, speech_data_.GetNextBlock(),
+                           kOpus20msFrameSamples, opus_mono_decoder_,
+                           output_data_decode, &audio_type));
+    // If not DTX, it should never enter DTX mode. If DTX, we do not care since
+    // whether it enters DTX depends on the signal type.
+    if (!dtx) {
+      EXPECT_GT(encoded_bytes_, 1);
+      EXPECT_EQ(0, opus_mono_encoder_->in_dtx_mode);
+      EXPECT_EQ(0, opus_mono_decoder_->in_dtx_mode);
+      EXPECT_EQ(0, audio_type);  // Speech.
+    }
+  }
+
+  // We input some silent segments. In DTX mode, the encoder will stop sending.
+  // However, DTX may happen after a while.
+  for (int i = 0; i < 21; ++i) {
+    EXPECT_EQ(kOpus20msFrameSamples,
+              EncodeDecode(opus_mono_encoder_, silence,
+                           kOpus20msFrameSamples, opus_mono_decoder_,
+                           output_data_decode, &audio_type));
+    if (!dtx) {
+      EXPECT_GT(encoded_bytes_, 1);
+      EXPECT_EQ(0, opus_mono_encoder_->in_dtx_mode);
+      EXPECT_EQ(0, opus_mono_decoder_->in_dtx_mode);
+      EXPECT_EQ(0, audio_type);  // Speech.
+    }
+  }
+
+  // For this input signal, DTX happens now.
+  EXPECT_EQ(kOpus20msFrameSamples,
+            EncodeDecode(opus_mono_encoder_, silence,
+                         kOpus20msFrameSamples, opus_mono_decoder_,
+                         output_data_decode, &audio_type));
+  if (dtx) {
+    EXPECT_EQ(1, encoded_bytes_);  // Send 1 byte.
+    EXPECT_EQ(1, opus_mono_encoder_->in_dtx_mode);
+    EXPECT_EQ(1, opus_mono_decoder_->in_dtx_mode);
+    EXPECT_EQ(2, audio_type);  // Comfort noise.
+  } else {
+    EXPECT_GT(encoded_bytes_, 1);
+    EXPECT_EQ(0, opus_mono_encoder_->in_dtx_mode);
+    EXPECT_EQ(0, opus_mono_decoder_->in_dtx_mode);
+    EXPECT_EQ(0, audio_type);  // Speech.
+  }
+
+  // DTX mode is maintained 400 ms.
+  for (int i = 0; i < 20; ++i) {
+    EXPECT_EQ(kOpus20msFrameSamples,
+              EncodeDecode(opus_mono_encoder_, silence,
+                           kOpus20msFrameSamples, opus_mono_decoder_,
+                           output_data_decode, &audio_type));
+    if (dtx) {
+      EXPECT_EQ(0, encoded_bytes_);  // Send 0 byte.
+      EXPECT_EQ(1, opus_mono_encoder_->in_dtx_mode);
+      EXPECT_EQ(1, opus_mono_decoder_->in_dtx_mode);
+      EXPECT_EQ(2, audio_type);  // Comfort noise.
+    } else {
+      EXPECT_GT(encoded_bytes_, 1);
+      EXPECT_EQ(0, opus_mono_encoder_->in_dtx_mode);
+      EXPECT_EQ(0, opus_mono_decoder_->in_dtx_mode);
+      EXPECT_EQ(0, audio_type);  // Speech.
+    }
+  }
+
+  // Quit DTX after 400 ms
+  EXPECT_EQ(kOpus20msFrameSamples,
+            EncodeDecode(opus_mono_encoder_, silence,
+                         kOpus20msFrameSamples, opus_mono_decoder_,
+                         output_data_decode, &audio_type));
+
+  EXPECT_GT(encoded_bytes_, 1);
+  EXPECT_EQ(0, opus_mono_encoder_->in_dtx_mode);
+  EXPECT_EQ(0, opus_mono_decoder_->in_dtx_mode);
+  EXPECT_EQ(0, audio_type);  // Speech.
+
+  // Enters DTX again immediately.
+  EXPECT_EQ(kOpus20msFrameSamples,
+            EncodeDecode(opus_mono_encoder_, silence,
+                         kOpus20msFrameSamples, opus_mono_decoder_,
+                         output_data_decode, &audio_type));
+  if (dtx) {
+    EXPECT_EQ(1, encoded_bytes_);  // Send 1 byte.
+    EXPECT_EQ(1, opus_mono_encoder_->in_dtx_mode);
+    EXPECT_EQ(1, opus_mono_decoder_->in_dtx_mode);
+    EXPECT_EQ(2, audio_type);  // Comfort noise.
+  } else {
+    EXPECT_GT(encoded_bytes_, 1);
+    EXPECT_EQ(0, opus_mono_encoder_->in_dtx_mode);
+    EXPECT_EQ(0, opus_mono_decoder_->in_dtx_mode);
+    EXPECT_EQ(0, audio_type);  // Speech.
+  }
+
+  silence[0] = 10000;
+  if (dtx) {
+    // Verify that encoder/decoder can jump out from DTX mode.
+    EXPECT_EQ(kOpus20msFrameSamples,
+              EncodeDecode(opus_mono_encoder_, silence,
+                           kOpus20msFrameSamples, opus_mono_decoder_,
+                           output_data_decode, &audio_type));
+    EXPECT_GT(encoded_bytes_, 1);
+    EXPECT_EQ(0, opus_mono_encoder_->in_dtx_mode);
+    EXPECT_EQ(0, opus_mono_decoder_->in_dtx_mode);
+    EXPECT_EQ(0, audio_type);  // Speech.
+  }
+
+  // Free memory.
+  EXPECT_EQ(0, WebRtcOpus_EncoderFree(opus_mono_encoder_));
+  EXPECT_EQ(0, WebRtcOpus_DecoderFree(opus_mono_decoder_));
+}
+
 // Test failing Create.
 TEST_F(OpusTest, OpusCreateFail) {
   // Test to see that an invalid pointer is caught.
@@ -110,6 +274,8 @@
 }
 
 TEST_F(OpusTest, OpusEncodeDecodeMono) {
+  PrepareSpeechData(1, 20, 20);
+
   // Create encoder memory.
   EXPECT_EQ(0, WebRtcOpus_EncoderCreate(&opus_mono_encoder_, 1));
   EXPECT_EQ(0, WebRtcOpus_DecoderCreate(&opus_mono_decoder_, 1));
@@ -121,16 +287,12 @@
   EXPECT_EQ(1, WebRtcOpus_DecoderChannels(opus_mono_decoder_));
 
   // Encode & decode.
-  int16_t encoded_bytes;
   int16_t audio_type;
-  int16_t output_data_decode[kOpusMaxFrameSamples];
-  encoded_bytes = WebRtcOpus_Encode(opus_mono_encoder_, speech_data_,
-                                    kOpus20msFrameSamples, kMaxBytes,
-                                    bitstream_);
+  int16_t output_data_decode[kOpus20msFrameSamples];
   EXPECT_EQ(kOpus20msFrameSamples,
-            WebRtcOpus_Decode(opus_mono_decoder_, bitstream_,
-                              encoded_bytes, output_data_decode,
-                              &audio_type));
+            EncodeDecode(opus_mono_encoder_, speech_data_.GetNextBlock(),
+                         kOpus20msFrameSamples, opus_mono_decoder_,
+                         output_data_decode, &audio_type));
 
   // Free memory.
   EXPECT_EQ(0, WebRtcOpus_EncoderFree(opus_mono_encoder_));
@@ -138,6 +300,8 @@
 }
 
 TEST_F(OpusTest, OpusEncodeDecodeStereo) {
+  PrepareSpeechData(2, 20, 20);
+
   // Create encoder memory.
   EXPECT_EQ(0, WebRtcOpus_EncoderCreate(&opus_stereo_encoder_, 2));
   EXPECT_EQ(0, WebRtcOpus_DecoderCreate(&opus_stereo_decoder_, 2));
@@ -149,16 +313,12 @@
   EXPECT_EQ(2, WebRtcOpus_DecoderChannels(opus_stereo_decoder_));
 
   // Encode & decode.
-  int16_t encoded_bytes;
   int16_t audio_type;
-  int16_t output_data_decode[kOpusMaxFrameSamples];
-  encoded_bytes = WebRtcOpus_Encode(opus_stereo_encoder_, speech_data_,
-                                    kOpus20msFrameSamples, kMaxBytes,
-                                    bitstream_);
+  int16_t output_data_decode[kOpus20msFrameSamples * 2];
   EXPECT_EQ(kOpus20msFrameSamples,
-            WebRtcOpus_Decode(opus_stereo_decoder_, bitstream_,
-                              encoded_bytes, output_data_decode,
-                              &audio_type));
+            EncodeDecode(opus_stereo_encoder_, speech_data_.GetNextBlock(),
+                         kOpus20msFrameSamples, opus_stereo_decoder_,
+                         output_data_decode, &audio_type));
 
   // Free memory.
   EXPECT_EQ(0, WebRtcOpus_EncoderFree(opus_stereo_encoder_));
@@ -207,28 +367,25 @@
 // Encode and decode one frame (stereo), initialize the decoder and
 // decode once more.
 TEST_F(OpusTest, OpusDecodeInit) {
+  PrepareSpeechData(2, 20, 20);
+
   // Create encoder memory.
   EXPECT_EQ(0, WebRtcOpus_EncoderCreate(&opus_stereo_encoder_, 2));
   EXPECT_EQ(0, WebRtcOpus_DecoderCreate(&opus_stereo_decoder_, 2));
 
   // Encode & decode.
-  int16_t encoded_bytes;
   int16_t audio_type;
-  int16_t output_data_decode[kOpusMaxFrameSamples];
-
-  encoded_bytes = WebRtcOpus_Encode(opus_stereo_encoder_, speech_data_,
-                                    kOpus20msFrameSamples, kMaxBytes,
-                                    bitstream_);
+  int16_t output_data_decode[kOpus20msFrameSamples * 2];
   EXPECT_EQ(kOpus20msFrameSamples,
-            WebRtcOpus_Decode(opus_stereo_decoder_, bitstream_,
-                              encoded_bytes, output_data_decode,
-                              &audio_type));
+            EncodeDecode(opus_stereo_encoder_, speech_data_.GetNextBlock(),
+                         kOpus20msFrameSamples, opus_stereo_decoder_,
+                         output_data_decode, &audio_type));
 
   EXPECT_EQ(0, WebRtcOpus_DecoderInit(opus_stereo_decoder_));
 
   EXPECT_EQ(kOpus20msFrameSamples,
             WebRtcOpus_Decode(opus_stereo_decoder_, bitstream_,
-                              encoded_bytes, output_data_decode,
+                              encoded_bytes_, output_data_decode,
                               &audio_type));
 
   // Free memory.
@@ -255,6 +412,61 @@
   EXPECT_EQ(0, WebRtcOpus_EncoderFree(opus_stereo_encoder_));
 }
 
+TEST_F(OpusTest, OpusEnableDisableDtx) {
+  // Test without creating encoder memory.
+  EXPECT_EQ(-1, WebRtcOpus_EnableDtx(opus_mono_encoder_));
+  EXPECT_EQ(-1, WebRtcOpus_DisableDtx(opus_stereo_encoder_));
+
+  // Create encoder memory, try with different bitrates.
+  EXPECT_EQ(0, WebRtcOpus_EncoderCreate(&opus_mono_encoder_, 1));
+  EXPECT_EQ(0, WebRtcOpus_EncoderCreate(&opus_stereo_encoder_, 2));
+
+  opus_int32 dtx;
+
+  // DTX is off by default.
+  opus_encoder_ctl(opus_mono_encoder_->encoder,
+                   OPUS_GET_DTX(&dtx));
+  EXPECT_EQ(0, dtx);
+
+  opus_encoder_ctl(opus_stereo_encoder_->encoder,
+                   OPUS_GET_DTX(&dtx));
+  EXPECT_EQ(0, dtx);
+
+  // Test to enable DTX.
+  EXPECT_EQ(0, WebRtcOpus_EnableDtx(opus_mono_encoder_));
+  opus_encoder_ctl(opus_mono_encoder_->encoder,
+                   OPUS_GET_DTX(&dtx));
+  EXPECT_EQ(1, dtx);
+
+  EXPECT_EQ(0, WebRtcOpus_EnableDtx(opus_stereo_encoder_));
+  opus_encoder_ctl(opus_stereo_encoder_->encoder,
+                   OPUS_GET_DTX(&dtx));
+  EXPECT_EQ(1, dtx);
+
+  // Test to disable DTX.
+  EXPECT_EQ(0, WebRtcOpus_DisableDtx(opus_mono_encoder_));
+  opus_encoder_ctl(opus_mono_encoder_->encoder,
+                   OPUS_GET_DTX(&dtx));
+  EXPECT_EQ(0, dtx);
+
+  EXPECT_EQ(0, WebRtcOpus_DisableDtx(opus_stereo_encoder_));
+  opus_encoder_ctl(opus_stereo_encoder_->encoder,
+                   OPUS_GET_DTX(&dtx));
+  EXPECT_EQ(0, dtx);
+
+  // Free memory.
+  EXPECT_EQ(0, WebRtcOpus_EncoderFree(opus_mono_encoder_));
+  EXPECT_EQ(0, WebRtcOpus_EncoderFree(opus_stereo_encoder_));
+}
+
+TEST_F(OpusTest, OpusDtxOff) {
+  TestDtxEffect(false);
+}
+
+TEST_F(OpusTest, OpusDtxOn) {
+  TestDtxEffect(true);
+}
+
 TEST_F(OpusTest, OpusSetPacketLossRate) {
   // Test without creating encoder memory.
   EXPECT_EQ(-1, WebRtcOpus_SetPacketLossRate(opus_mono_encoder_, 50));
@@ -303,6 +515,8 @@
 
 // PLC in mono mode.
 TEST_F(OpusTest, OpusDecodePlcMono) {
+  PrepareSpeechData(1, 20, 20);
+
   // Create encoder memory.
   EXPECT_EQ(0, WebRtcOpus_EncoderCreate(&opus_mono_encoder_, 1));
   EXPECT_EQ(0, WebRtcOpus_DecoderCreate(&opus_mono_decoder_, 1));
@@ -314,19 +528,15 @@
   EXPECT_EQ(1, WebRtcOpus_DecoderChannels(opus_mono_decoder_));
 
   // Encode & decode.
-  int16_t encoded_bytes;
   int16_t audio_type;
-  int16_t output_data_decode[kOpusMaxFrameSamples];
-  encoded_bytes = WebRtcOpus_Encode(opus_mono_encoder_, speech_data_,
-                                    kOpus20msFrameSamples, kMaxBytes,
-                                    bitstream_);
+  int16_t output_data_decode[kOpus20msFrameSamples];
   EXPECT_EQ(kOpus20msFrameSamples,
-            WebRtcOpus_Decode(opus_mono_decoder_, bitstream_,
-                              encoded_bytes, output_data_decode,
-                              &audio_type));
+            EncodeDecode(opus_mono_encoder_, speech_data_.GetNextBlock(),
+                         kOpus20msFrameSamples, opus_mono_decoder_,
+                         output_data_decode, &audio_type));
 
   // Call decoder PLC.
-  int16_t plc_buffer[kOpusMaxFrameSamples];
+  int16_t plc_buffer[kOpus20msFrameSamples];
   EXPECT_EQ(kOpus20msFrameSamples,
             WebRtcOpus_DecodePlc(opus_mono_decoder_, plc_buffer, 1));
 
@@ -337,6 +547,8 @@
 
 // PLC in stereo mode.
 TEST_F(OpusTest, OpusDecodePlcStereo) {
+  PrepareSpeechData(2, 20, 20);
+
   // Create encoder memory.
   EXPECT_EQ(0, WebRtcOpus_EncoderCreate(&opus_stereo_encoder_, 2));
   EXPECT_EQ(0, WebRtcOpus_DecoderCreate(&opus_stereo_decoder_, 2));
@@ -348,19 +560,15 @@
   EXPECT_EQ(2, WebRtcOpus_DecoderChannels(opus_stereo_decoder_));
 
   // Encode & decode.
-  int16_t encoded_bytes;
   int16_t audio_type;
-  int16_t output_data_decode[kOpusMaxFrameSamples];
-  encoded_bytes = WebRtcOpus_Encode(opus_stereo_encoder_, speech_data_,
-                                    kOpus20msFrameSamples, kMaxBytes,
-                                    bitstream_);
+  int16_t output_data_decode[kOpus20msFrameSamples * 2];
   EXPECT_EQ(kOpus20msFrameSamples,
-            WebRtcOpus_Decode(opus_stereo_decoder_, bitstream_,
-                              encoded_bytes, output_data_decode,
-                              &audio_type));
+            EncodeDecode(opus_stereo_encoder_, speech_data_.GetNextBlock(),
+                         kOpus20msFrameSamples, opus_stereo_decoder_,
+                         output_data_decode, &audio_type));
 
   // Call decoder PLC.
-  int16_t plc_buffer[kOpusMaxFrameSamples];
+  int16_t plc_buffer[kOpus20msFrameSamples * 2];
   EXPECT_EQ(kOpus20msFrameSamples,
             WebRtcOpus_DecodePlc(opus_stereo_decoder_, plc_buffer, 1));
 
@@ -371,27 +579,29 @@
 
 // Duration estimation.
 TEST_F(OpusTest, OpusDurationEstimation) {
+  PrepareSpeechData(2, 20, 20);
+
   // Create.
   EXPECT_EQ(0, WebRtcOpus_EncoderCreate(&opus_stereo_encoder_, 2));
   EXPECT_EQ(0, WebRtcOpus_DecoderCreate(&opus_stereo_decoder_, 2));
 
-  int16_t encoded_bytes;
-
-  // 10 ms.
-  encoded_bytes = WebRtcOpus_Encode(opus_stereo_encoder_, speech_data_,
-                                    kOpus10msFrameSamples, kMaxBytes,
-                                    bitstream_);
+  // 10 ms. We use only first 10 ms of a 20 ms block.
+  encoded_bytes_ = WebRtcOpus_Encode(opus_stereo_encoder_,
+                                     speech_data_.GetNextBlock(),
+                                     kOpus10msFrameSamples, kMaxBytes,
+                                     bitstream_);
   EXPECT_EQ(kOpus10msFrameSamples,
             WebRtcOpus_DurationEst(opus_stereo_decoder_, bitstream_,
-                                   encoded_bytes));
+                                   encoded_bytes_));
 
   // 20 ms
-  encoded_bytes = WebRtcOpus_Encode(opus_stereo_encoder_, speech_data_,
-                                    kOpus20msFrameSamples, kMaxBytes,
-                                    bitstream_);
+  encoded_bytes_ = WebRtcOpus_Encode(opus_stereo_encoder_,
+                                     speech_data_.GetNextBlock(),
+                                     kOpus20msFrameSamples, kMaxBytes,
+                                     bitstream_);
   EXPECT_EQ(kOpus20msFrameSamples,
             WebRtcOpus_DurationEst(opus_stereo_decoder_, bitstream_,
-                                   encoded_bytes));
+                                   encoded_bytes_));
 
   // Free memory.
   EXPECT_EQ(0, WebRtcOpus_EncoderFree(opus_stereo_encoder_));
diff --git a/modules/audio_coding/neteq/test/neteq_opus_fec_quality_test.cc b/modules/audio_coding/neteq/test/neteq_opus_fec_quality_test.cc
index dee99b8..eddbffd 100644
--- a/modules/audio_coding/neteq/test/neteq_opus_fec_quality_test.cc
+++ b/modules/audio_coding/neteq/test/neteq_opus_fec_quality_test.cc
@@ -111,6 +111,8 @@
 
 DEFINE_bool(fec, true, "Whether to enable FEC for encoding.");
 
+DEFINE_bool(dtx, true, "Whether to enable DTX for encoding.");
+
 class NetEqOpusFecQualityTest : public NetEqQualityTest {
  protected:
   NetEqOpusFecQualityTest();
@@ -123,6 +125,7 @@
   int channels_;
   int bit_rate_kbps_;
   bool fec_;
+  bool dtx_;
   int target_loss_rate_;
 };
 
@@ -137,6 +140,7 @@
       channels_(FLAGS_channels),
       bit_rate_kbps_(FLAGS_bit_rate_kbps),
       fec_(FLAGS_fec),
+      dtx_(FLAGS_dtx),
       target_loss_rate_(FLAGS_reported_loss_rate) {
 }
 
@@ -149,6 +153,9 @@
   if (fec_) {
     EXPECT_EQ(0, WebRtcOpus_EnableFec(opus_encoder_));
   }
+  if (dtx_) {
+    EXPECT_EQ(0, WebRtcOpus_EnableDtx(opus_encoder_));
+  }
   EXPECT_EQ(0, WebRtcOpus_SetPacketLossRate(opus_encoder_,
                                             target_loss_rate_));
   NetEqQualityTest::SetUp();
@@ -166,7 +173,6 @@
   int value = WebRtcOpus_Encode(opus_encoder_, in_data,
                                 block_size_samples, max_bytes,
                                 payload);
-  EXPECT_GT(value, 0);
   return value;
 }