diff --git a/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.cc b/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.cc
index 0660993..d8384aa 100644
--- a/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.cc
+++ b/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.cc
@@ -133,7 +133,7 @@
   if (!HaveValidEncoder("Process"))
     return -1;
 
-  AudioEncoder* audio_encoder = codec_manager_.CurrentEncoder();
+  AudioEncoder* audio_encoder = rent_a_codec_.GetEncoderStack();
   // Scale the timestamp to the codec's RTP timestamp rate.
   uint32_t rtp_timestamp =
       first_frame_ ? input_data.input_timestamp
@@ -198,19 +198,43 @@
 // Can be called multiple times for Codec, CNG, RED.
 int AudioCodingModuleImpl::RegisterSendCodec(const CodecInst& send_codec) {
   CriticalSectionScoped lock(acm_crit_sect_.get());
-  return codec_manager_.RegisterEncoder(send_codec);
+  if (!codec_manager_.RegisterEncoder(send_codec)) {
+    return -1;
+  }
+  auto* sp = codec_manager_.GetStackParams();
+  if (!sp->speech_encoder && codec_manager_.GetCodecInst()) {
+    // We have no speech encoder, but we have a specification for making one.
+    AudioEncoder* enc =
+        rent_a_codec_.RentEncoder(*codec_manager_.GetCodecInst());
+    if (!enc)
+      return -1;
+    sp->speech_encoder = enc;
+  }
+  if (sp->speech_encoder)
+    rent_a_codec_.RentEncoderStack(sp);
+  return 0;
 }
 
 void AudioCodingModuleImpl::RegisterExternalSendCodec(
     AudioEncoder* external_speech_encoder) {
   CriticalSectionScoped lock(acm_crit_sect_.get());
-  codec_manager_.RegisterEncoder(external_speech_encoder);
+  auto* sp = codec_manager_.GetStackParams();
+  sp->speech_encoder = external_speech_encoder;
+  rent_a_codec_.RentEncoderStack(sp);
 }
 
 // Get current send codec.
 rtc::Optional<CodecInst> AudioCodingModuleImpl::SendCodec() const {
   CriticalSectionScoped lock(acm_crit_sect_.get());
-  return codec_manager_.GetCodecInst();
+  auto* ci = codec_manager_.GetCodecInst();
+  if (ci) {
+    return rtc::Optional<CodecInst>(*ci);
+  }
+  auto* enc = codec_manager_.GetStackParams()->speech_encoder;
+  if (enc) {
+    return rtc::Optional<CodecInst>(CodecManager::ForgeCodecInst(enc));
+  }
+  return rtc::Optional<CodecInst>();
 }
 
 // Get current send frequency.
@@ -219,19 +243,21 @@
                "SendFrequency()");
   CriticalSectionScoped lock(acm_crit_sect_.get());
 
-  if (!codec_manager_.CurrentEncoder()) {
+  const auto* enc = rent_a_codec_.GetEncoderStack();
+  if (!enc) {
     WEBRTC_TRACE(webrtc::kTraceStream, webrtc::kTraceAudioCoding, id_,
                  "SendFrequency Failed, no codec is registered");
     return -1;
   }
 
-  return codec_manager_.CurrentEncoder()->SampleRateHz();
+  return enc->SampleRateHz();
 }
 
 void AudioCodingModuleImpl::SetBitRate(int bitrate_bps) {
   CriticalSectionScoped lock(acm_crit_sect_.get());
-  if (codec_manager_.CurrentEncoder()) {
-    codec_manager_.CurrentEncoder()->SetTargetBitrate(bitrate_bps);
+  auto* enc = rent_a_codec_.GetEncoderStack();
+  if (enc) {
+    enc->SetTargetBitrate(bitrate_bps);
   }
 }
 
@@ -298,10 +324,12 @@
   }
 
   // Check whether we need an up-mix or down-mix?
-  bool remix = ptr_frame->num_channels_ !=
-               codec_manager_.CurrentEncoder()->NumChannels();
+  const int current_num_channels =
+      rent_a_codec_.GetEncoderStack()->NumChannels();
+  const bool same_num_channels =
+      ptr_frame->num_channels_ == current_num_channels;
 
-  if (remix) {
+  if (!same_num_channels) {
     if (ptr_frame->num_channels_ == 1) {
       if (UpMix(*ptr_frame, WEBRTC_10MS_PCM_AUDIO, input_data->buffer) < 0)
         return -1;
@@ -316,14 +344,13 @@
   const int16_t* ptr_audio = ptr_frame->data_;
 
   // For pushing data to primary, point the |ptr_audio| to correct buffer.
-  if (codec_manager_.CurrentEncoder()->NumChannels() !=
-      ptr_frame->num_channels_)
+  if (!same_num_channels)
     ptr_audio = input_data->buffer;
 
   input_data->input_timestamp = ptr_frame->timestamp_;
   input_data->audio = ptr_audio;
   input_data->length_per_channel = ptr_frame->samples_per_channel_;
-  input_data->audio_channel = codec_manager_.CurrentEncoder()->NumChannels();
+  input_data->audio_channel = current_num_channels;
 
   return 0;
 }
@@ -335,13 +362,14 @@
 // is required, |*ptr_out| points to |in_frame|.
 int AudioCodingModuleImpl::PreprocessToAddData(const AudioFrame& in_frame,
                                                const AudioFrame** ptr_out) {
-  bool resample = (in_frame.sample_rate_hz_ !=
-                   codec_manager_.CurrentEncoder()->SampleRateHz());
+  const auto* enc = rent_a_codec_.GetEncoderStack();
+  const bool resample = in_frame.sample_rate_hz_ != enc->SampleRateHz();
 
   // This variable is true if primary codec and secondary codec (if exists)
   // are both mono and input is stereo.
-  bool down_mix = (in_frame.num_channels_ == 2) &&
-                  (codec_manager_.CurrentEncoder()->NumChannels() == 1);
+  // TODO(henrik.lundin): This condition should probably be
+  //   in_frame.num_channels_ > enc->NumChannels()
+  const bool down_mix = in_frame.num_channels_ == 2 && enc->NumChannels() == 1;
 
   if (!first_10ms_data_) {
     expected_in_ts_ = in_frame.timestamp_;
@@ -351,10 +379,8 @@
     // TODO(turajs): Do we need a warning here.
     expected_codec_ts_ +=
         (in_frame.timestamp_ - expected_in_ts_) *
-        static_cast<uint32_t>(
-            (static_cast<double>(
-                 codec_manager_.CurrentEncoder()->SampleRateHz()) /
-             static_cast<double>(in_frame.sample_rate_hz_)));
+        static_cast<uint32_t>(static_cast<double>(enc->SampleRateHz()) /
+                              static_cast<double>(in_frame.sample_rate_hz_));
     expected_in_ts_ = in_frame.timestamp_;
   }
 
@@ -393,8 +419,7 @@
     dest_ptr_audio = preprocess_frame_.data_;
 
     int samples_per_channel = resampler_.Resample10Msec(
-        src_ptr_audio, in_frame.sample_rate_hz_,
-        codec_manager_.CurrentEncoder()->SampleRateHz(),
+        src_ptr_audio, in_frame.sample_rate_hz_, enc->SampleRateHz(),
         preprocess_frame_.num_channels_, AudioFrame::kMaxDataSizeSamples,
         dest_ptr_audio);
 
@@ -405,8 +430,7 @@
     }
     preprocess_frame_.samples_per_channel_ =
         static_cast<size_t>(samples_per_channel);
-    preprocess_frame_.sample_rate_hz_ =
-        codec_manager_.CurrentEncoder()->SampleRateHz();
+    preprocess_frame_.sample_rate_hz_ = enc->SampleRateHz();
   }
 
   expected_codec_ts_ +=
@@ -422,17 +446,21 @@
 
 bool AudioCodingModuleImpl::REDStatus() const {
   CriticalSectionScoped lock(acm_crit_sect_.get());
-  return codec_manager_.red_enabled();
+  return codec_manager_.GetStackParams()->use_red;
 }
 
 // Configure RED status i.e on/off.
-int AudioCodingModuleImpl::SetREDStatus(
+int AudioCodingModuleImpl::SetREDStatus(bool enable_red) {
 #ifdef WEBRTC_CODEC_RED
-    bool enable_red) {
   CriticalSectionScoped lock(acm_crit_sect_.get());
-  return codec_manager_.SetCopyRed(enable_red) ? 0 : -1;
+  if (!codec_manager_.SetCopyRed(enable_red)) {
+    return -1;
+  }
+  auto* sp = codec_manager_.GetStackParams();
+  if (sp->speech_encoder)
+    rent_a_codec_.RentEncoderStack(sp);
+  return 0;
 #else
-    bool /* enable_red */) {
   WEBRTC_TRACE(webrtc::kTraceWarning, webrtc::kTraceAudioCoding, id_,
                "  WEBRTC_CODEC_RED is undefined");
   return -1;
@@ -445,18 +473,29 @@
 
 bool AudioCodingModuleImpl::CodecFEC() const {
   CriticalSectionScoped lock(acm_crit_sect_.get());
-  return codec_manager_.codec_fec_enabled();
+  return codec_manager_.GetStackParams()->use_codec_fec;
 }
 
 int AudioCodingModuleImpl::SetCodecFEC(bool enable_codec_fec) {
   CriticalSectionScoped lock(acm_crit_sect_.get());
-  return codec_manager_.SetCodecFEC(enable_codec_fec);
+  if (!codec_manager_.SetCodecFEC(enable_codec_fec)) {
+    return -1;
+  }
+  auto* sp = codec_manager_.GetStackParams();
+  if (sp->speech_encoder)
+    rent_a_codec_.RentEncoderStack(sp);
+  if (enable_codec_fec) {
+    return sp->use_codec_fec ? 0 : -1;
+  } else {
+    RTC_DCHECK(!sp->use_codec_fec);
+    return 0;
+  }
 }
 
 int AudioCodingModuleImpl::SetPacketLossRate(int loss_rate) {
   CriticalSectionScoped lock(acm_crit_sect_.get());
   if (HaveValidEncoder("SetPacketLossRate")) {
-    codec_manager_.CurrentEncoder()->SetProjectedPacketLossRate(loss_rate /
+    rent_a_codec_.GetEncoderStack()->SetProjectedPacketLossRate(loss_rate /
                                                                 100.0);
   }
   return 0;
@@ -471,14 +510,22 @@
   // Note: |enable_vad| is not used; VAD is enabled based on the DTX setting.
   RTC_DCHECK_EQ(enable_dtx, enable_vad);
   CriticalSectionScoped lock(acm_crit_sect_.get());
-  return codec_manager_.SetVAD(enable_dtx, mode);
+  if (!codec_manager_.SetVAD(enable_dtx, mode)) {
+    return -1;
+  }
+  auto* sp = codec_manager_.GetStackParams();
+  if (sp->speech_encoder)
+    rent_a_codec_.RentEncoderStack(sp);
+  return 0;
 }
 
 // Get VAD/DTX settings.
 int AudioCodingModuleImpl::VAD(bool* dtx_enabled, bool* vad_enabled,
                                ACMVADMode* mode) const {
   CriticalSectionScoped lock(acm_crit_sect_.get());
-  codec_manager_.VAD(dtx_enabled, vad_enabled, mode);
+  const auto* sp = codec_manager_.GetStackParams();
+  *dtx_enabled = *vad_enabled = sp->use_cng;
+  *mode = sp->vad_mode;
   return 0;
 }
 
@@ -565,9 +612,11 @@
 
   // Get |decoder| associated with |codec|. |decoder| is NULL if |codec| does
   // not own its decoder.
-  return receiver_.AddCodec(*codec_index, codec.pltype, codec.channels,
-                            codec.plfreq, codec_manager_.GetAudioDecoder(codec),
-                            codec.plname);
+  return receiver_.AddCodec(
+      *codec_index, codec.pltype, codec.channels, codec.plfreq,
+      STR_CASE_CMP(codec.plname, "isac") == 0 ? rent_a_codec_.RentIsacDecoder()
+                                              : nullptr,
+      codec.plname);
 }
 
 int AudioCodingModuleImpl::RegisterExternalReceiveCodec(
@@ -709,7 +758,7 @@
       FATAL();
       return 0;
   }
-  return codec_manager_.CurrentEncoder()->SetApplication(app) ? 0 : -1;
+  return rent_a_codec_.GetEncoderStack()->SetApplication(app) ? 0 : -1;
 }
 
 // Informs Opus encoder of the maximum playback rate the receiver will render.
@@ -720,7 +769,7 @@
   }
   if (!codec_manager_.CurrentEncoderIsOpus())
     return -1;
-  codec_manager_.CurrentEncoder()->SetMaxPlaybackRate(frequency_hz);
+  rent_a_codec_.GetEncoderStack()->SetMaxPlaybackRate(frequency_hz);
   return 0;
 }
 
@@ -731,7 +780,7 @@
   }
   if (!codec_manager_.CurrentEncoderIsOpus())
     return -1;
-  return codec_manager_.CurrentEncoder()->SetDtx(true) ? 0 : -1;
+  return rent_a_codec_.GetEncoderStack()->SetDtx(true) ? 0 : -1;
 }
 
 int AudioCodingModuleImpl::DisableOpusDtx() {
@@ -741,7 +790,7 @@
   }
   if (!codec_manager_.CurrentEncoderIsOpus())
     return -1;
-  return codec_manager_.CurrentEncoder()->SetDtx(false) ? 0 : -1;
+  return rent_a_codec_.GetEncoderStack()->SetDtx(false) ? 0 : -1;
 }
 
 int AudioCodingModuleImpl::PlayoutTimestamp(uint32_t* timestamp) {
@@ -749,7 +798,7 @@
 }
 
 bool AudioCodingModuleImpl::HaveValidEncoder(const char* caller_name) const {
-  if (!codec_manager_.CurrentEncoder()) {
+  if (!rent_a_codec_.GetEncoderStack()) {
     WEBRTC_TRACE(webrtc::kTraceError, webrtc::kTraceAudioCoding, id_,
                  "%s failed: No send codec is registered.", caller_name);
     return false;
diff --git a/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h b/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
index a624b23..337ff13 100644
--- a/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
+++ b/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
@@ -249,6 +249,7 @@
   AcmReceiver receiver_;  // AcmReceiver has it's own internal lock.
   ChangeLogger bitrate_logger_ GUARDED_BY(acm_crit_sect_);
   CodecManager codec_manager_ GUARDED_BY(acm_crit_sect_);
+  RentACodec rent_a_codec_ GUARDED_BY(acm_crit_sect_);
 
   // This is to keep track of CN instances where we can send DTMFs.
   uint8_t previous_pltype_ GUARDED_BY(acm_crit_sect_);
diff --git a/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest_oldapi.cc b/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest_oldapi.cc
index 01bdcc0..8de6c91 100644
--- a/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest_oldapi.cc
+++ b/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest_oldapi.cc
@@ -1619,10 +1619,6 @@
       .Times(AtLeast(1))
       .WillRepeatedly(
           Invoke(&encoder, &AudioEncoderPcmU::Num10MsFramesInNextPacket));
-  EXPECT_CALL(mock_encoder, Max10MsFramesInAPacket())
-      .Times(AtLeast(1))
-      .WillRepeatedly(
-          Invoke(&encoder, &AudioEncoderPcmU::Max10MsFramesInAPacket));
   EXPECT_CALL(mock_encoder, GetTargetBitrate())
       .Times(AtLeast(1))
       .WillRepeatedly(Invoke(&encoder, &AudioEncoderPcmU::GetTargetBitrate));
diff --git a/webrtc/modules/audio_coding/acm2/codec_manager.cc b/webrtc/modules/audio_coding/acm2/codec_manager.cc
index 19a79c2..bc507dd 100644
--- a/webrtc/modules/audio_coding/acm2/codec_manager.cc
+++ b/webrtc/modules/audio_coding/acm2/codec_manager.cc
@@ -55,14 +55,6 @@
   return RentACodec::CodecIndexFromId(*maybe_codec_id).value_or(-1);
 }
 
-bool IsIsac(const CodecInst& codec) {
-  return
-#if (defined(WEBRTC_CODEC_ISAC) || defined(WEBRTC_CODEC_ISACFX))
-      !STR_CASE_CMP(codec.plname, "isac") ||
-#endif
-      false;
-}
-
 bool IsOpus(const CodecInst& codec) {
   return
 #ifdef WEBRTC_CODEC_OPUS
@@ -71,138 +63,73 @@
       false;
 }
 
-bool IsPcmU(const CodecInst& codec) {
-  return !STR_CASE_CMP(codec.plname, "pcmu");
-}
-
-bool IsPcmA(const CodecInst& codec) {
-  return !STR_CASE_CMP(codec.plname, "pcma");
-}
-
-bool IsPcm16B(const CodecInst& codec) {
-  return !STR_CASE_CMP(codec.plname, "l16");
-}
-
-bool IsIlbc(const CodecInst& codec) {
-  return
-#ifdef WEBRTC_CODEC_ILBC
-      !STR_CASE_CMP(codec.plname, "ilbc") ||
-#endif
-      false;
-}
-
-bool IsG722(const CodecInst& codec) {
-  return
-#ifdef WEBRTC_CODEC_G722
-      !STR_CASE_CMP(codec.plname, "g722") ||
-#endif
-      false;
-}
-
-bool CodecSupported(const CodecInst& codec) {
-  return IsOpus(codec) || IsPcmU(codec) || IsPcmA(codec) || IsPcm16B(codec) ||
-         IsIlbc(codec) || IsG722(codec) || IsIsac(codec);
-}
-
-const CodecInst kEmptyCodecInst = {-1, "noCodecRegistered", 0, 0, 0, 0};
 }  // namespace
 
-CodecManager::CodecManager()
-    : send_codec_inst_(kEmptyCodecInst), encoder_is_opus_(false) {
+CodecManager::CodecManager() {
   thread_checker_.DetachFromThread();
 }
 
 CodecManager::~CodecManager() = default;
 
-int CodecManager::RegisterEncoder(const CodecInst& send_codec) {
+bool CodecManager::RegisterEncoder(const CodecInst& send_codec) {
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
   int codec_id = IsValidSendCodec(send_codec);
 
   // Check for reported errors from function IsValidSendCodec().
   if (codec_id < 0) {
-    return -1;
+    return false;
   }
 
   int dummy_id = 0;
   switch (RentACodec::RegisterRedPayloadType(
       &codec_stack_params_.red_payload_types, send_codec)) {
     case RentACodec::RegistrationResult::kOk:
-      return 0;
+      return true;
     case RentACodec::RegistrationResult::kBadFreq:
       WEBRTC_TRACE(webrtc::kTraceError, webrtc::kTraceAudioCoding, dummy_id,
                    "RegisterSendCodec() failed, invalid frequency for RED"
                    " registration");
-      return -1;
+      return false;
     case RentACodec::RegistrationResult::kSkip:
       break;
   }
   switch (RentACodec::RegisterCngPayloadType(
       &codec_stack_params_.cng_payload_types, send_codec)) {
     case RentACodec::RegistrationResult::kOk:
-      return 0;
+      return true;
     case RentACodec::RegistrationResult::kBadFreq:
       WEBRTC_TRACE(webrtc::kTraceError, webrtc::kTraceAudioCoding, dummy_id,
                    "RegisterSendCodec() failed, invalid frequency for CNG"
                    " registration");
-      return -1;
+      return false;
     case RentACodec::RegistrationResult::kSkip:
       break;
   }
 
-  encoder_is_opus_ = IsOpus(send_codec);
-  if (encoder_is_opus_) {
+  if (IsOpus(send_codec)) {
     // VAD/DTX not supported.
     codec_stack_params_.use_cng = false;
   }
 
-  // Recreate the encoder if anything except the send bitrate has changed.
-  if (!CurrentEncoder() || send_codec_inst_.pltype != send_codec.pltype ||
-      STR_CASE_CMP(send_codec_inst_.plname, send_codec.plname) != 0 ||
-      send_codec_inst_.plfreq != send_codec.plfreq ||
-      send_codec_inst_.pacsize != send_codec.pacsize ||
-      send_codec_inst_.channels != send_codec.channels) {
-    RTC_DCHECK(CodecSupported(send_codec));
-    AudioEncoder* enc = rent_a_codec_.RentEncoder(send_codec);
-    if (!enc)
-      return -1;
-    codec_stack_params_.speech_encoder = enc;
-    rent_a_codec_.RentEncoderStack(&codec_stack_params_);
-    RTC_DCHECK(CurrentEncoder());
-  }
-
-  send_codec_inst_ = send_codec;
-  CurrentEncoder()->SetTargetBitrate(send_codec_inst_.rate);
-  return 0;
+  send_codec_inst_ = rtc::Optional<CodecInst>(send_codec);
+  codec_stack_params_.speech_encoder = nullptr;  // Caller must recreate it.
+  return true;
 }
 
-void CodecManager::RegisterEncoder(AudioEncoder* external_speech_encoder) {
-  // Make up a CodecInst.
-  send_codec_inst_.channels = external_speech_encoder->NumChannels();
-  send_codec_inst_.plfreq = external_speech_encoder->SampleRateHz();
-  send_codec_inst_.pacsize = rtc::CheckedDivExact(
+CodecInst CodecManager::ForgeCodecInst(
+    const AudioEncoder* external_speech_encoder) {
+  CodecInst ci;
+  ci.channels = external_speech_encoder->NumChannels();
+  ci.plfreq = external_speech_encoder->SampleRateHz();
+  ci.pacsize = rtc::CheckedDivExact(
       static_cast<int>(external_speech_encoder->Max10MsFramesInAPacket() *
-                       send_codec_inst_.plfreq),
+                       ci.plfreq),
       100);
-  send_codec_inst_.pltype = -1;  // Not valid.
-  send_codec_inst_.rate = -1;    // Not valid.
+  ci.pltype = -1;  // Not valid.
+  ci.rate = -1;    // Not valid.
   static const char kName[] = "external";
-  memcpy(send_codec_inst_.plname, kName, sizeof(kName));
-
-  codec_stack_params_.speech_encoder = external_speech_encoder;
-  rent_a_codec_.RentEncoderStack(&codec_stack_params_);
-}
-
-rtc::Optional<CodecInst> CodecManager::GetCodecInst() const {
-  int dummy_id = 0;
-  WEBRTC_TRACE(webrtc::kTraceStream, webrtc::kTraceAudioCoding, dummy_id,
-               "SendCodec()");
-
-  if (!CurrentEncoder()) {
-    WEBRTC_TRACE(webrtc::kTraceStream, webrtc::kTraceAudioCoding, dummy_id,
-                 "SendCodec Failed, no codec is registered");
-    return rtc::Optional<CodecInst>();
-  }
-  return rtc::Optional<CodecInst>(send_codec_inst_);
+  memcpy(ci.plname, kName, sizeof(kName));
+  return ci;
 }
 
 bool CodecManager::SetCopyRed(bool enable) {
@@ -211,22 +138,18 @@
                  "Codec internal FEC and RED cannot be co-enabled.");
     return false;
   }
-  if (enable &&
-      codec_stack_params_.red_payload_types.count(send_codec_inst_.plfreq) <
+  if (enable && send_codec_inst_ &&
+      codec_stack_params_.red_payload_types.count(send_codec_inst_->plfreq) <
           1) {
     WEBRTC_TRACE(webrtc::kTraceWarning, webrtc::kTraceAudioCoding, 0,
-                 "Cannot enable RED at %i Hz.", send_codec_inst_.plfreq);
+                 "Cannot enable RED at %i Hz.", send_codec_inst_->plfreq);
     return false;
   }
-  if (codec_stack_params_.use_red != enable) {
-    codec_stack_params_.use_red = enable;
-    if (CurrentEncoder())
-      rent_a_codec_.RentEncoderStack(&codec_stack_params_);
-  }
+  codec_stack_params_.use_red = enable;
   return true;
 }
 
-int CodecManager::SetVAD(bool enable, ACMVADMode mode) {
+bool CodecManager::SetVAD(bool enable, ACMVADMode mode) {
   // Sanity check of the mode.
   RTC_DCHECK(mode == VADNormal || mode == VADLowBitrate || mode == VADAggr ||
              mode == VADVeryAggr);
@@ -240,49 +163,32 @@
   if (enable && stereo_send) {
     WEBRTC_TRACE(webrtc::kTraceError, webrtc::kTraceAudioCoding, 0,
                  "VAD/DTX not supported for stereo sending");
-    codec_stack_params_.use_cng = false;
-    return -1;
+    return false;
   }
 
-  // If a send codec is registered, set VAD/DTX for the codec.
-  if (IsOpus(send_codec_inst_)) {
-    // VAD/DTX not supported.
-    codec_stack_params_.use_cng = false;
-    return 0;
+  if (CurrentEncoderIsOpus()) {
+    // VAD/DTX not supported, but don't fail.
+    enable = false;
   }
 
-  if (codec_stack_params_.use_cng != enable ||
-      codec_stack_params_.vad_mode != mode) {
-    codec_stack_params_.use_cng = enable;
-    codec_stack_params_.vad_mode = mode;
-    if (codec_stack_params_.speech_encoder)
-      rent_a_codec_.RentEncoderStack(&codec_stack_params_);
-  }
-  return 0;
+  codec_stack_params_.use_cng = enable;
+  codec_stack_params_.vad_mode = mode;
+  return true;
 }
 
-void CodecManager::VAD(bool* dtx_enabled,
-                       bool* vad_enabled,
-                       ACMVADMode* mode) const {
-  *dtx_enabled = *vad_enabled = codec_stack_params_.use_cng;
-  *mode = codec_stack_params_.vad_mode;
-}
-
-int CodecManager::SetCodecFEC(bool enable_codec_fec) {
+bool CodecManager::SetCodecFEC(bool enable_codec_fec) {
   if (enable_codec_fec && codec_stack_params_.use_red) {
     WEBRTC_TRACE(webrtc::kTraceWarning, webrtc::kTraceAudioCoding, 0,
                  "Codec internal FEC and RED cannot be co-enabled.");
-    return -1;
+    return false;
   }
 
-  RTC_CHECK(CurrentEncoder());
-  codec_stack_params_.use_codec_fec =
-      CurrentEncoder()->SetFec(enable_codec_fec) && enable_codec_fec;
-  return codec_stack_params_.use_codec_fec == enable_codec_fec ? 0 : -1;
+  codec_stack_params_.use_codec_fec = enable_codec_fec;
+  return true;
 }
 
-AudioDecoder* CodecManager::GetAudioDecoder(const CodecInst& codec) {
-  return IsIsac(codec) ? rent_a_codec_.RentIsacDecoder() : nullptr;
+bool CodecManager::CurrentEncoderIsOpus() const {
+  return send_codec_inst_ ? IsOpus(*send_codec_inst_) : false;
 }
 
 }  // namespace acm2
diff --git a/webrtc/modules/audio_coding/acm2/codec_manager.h b/webrtc/modules/audio_coding/acm2/codec_manager.h
index 61832e4..ad96d1d 100644
--- a/webrtc/modules/audio_coding/acm2/codec_manager.h
+++ b/webrtc/modules/audio_coding/acm2/codec_manager.h
@@ -33,46 +33,33 @@
   CodecManager();
   ~CodecManager();
 
-  int RegisterEncoder(const CodecInst& send_codec);
+  // Parses the given specification. On success, returns true and updates the
+  // stored CodecInst and stack parameters; on error, returns false.
+  bool RegisterEncoder(const CodecInst& send_codec);
 
-  void RegisterEncoder(AudioEncoder* external_speech_encoder);
+  static CodecInst ForgeCodecInst(const AudioEncoder* external_speech_encoder);
 
-  rtc::Optional<CodecInst> GetCodecInst() const;
+  const CodecInst* GetCodecInst() const {
+    return send_codec_inst_ ? &*send_codec_inst_ : nullptr;
+  }
+  const RentACodec::StackParameters* GetStackParams() const {
+    return &codec_stack_params_;
+  }
+  RentACodec::StackParameters* GetStackParams() { return &codec_stack_params_; }
 
   bool SetCopyRed(bool enable);
 
-  int SetVAD(bool enable, ACMVADMode mode);
+  bool SetVAD(bool enable, ACMVADMode mode);
 
-  void VAD(bool* dtx_enabled, bool* vad_enabled, ACMVADMode* mode) const;
+  bool SetCodecFEC(bool enable_codec_fec);
 
-  int SetCodecFEC(bool enable_codec_fec);
-
-  // Returns a pointer to AudioDecoder of the given codec. For iSAC, encoding
-  // and decoding have to be performed on a shared codec instance. By calling
-  // this method, we get the codec instance that ACM owns.
-  // If |codec| does not share an instance between encoder and decoder, returns
-  // null.
-  AudioDecoder* GetAudioDecoder(const CodecInst& codec);
-
-  bool red_enabled() const { return codec_stack_params_.use_red; }
-
-  bool codec_fec_enabled() const { return codec_stack_params_.use_codec_fec; }
-
-  AudioEncoder* CurrentEncoder() { return rent_a_codec_.GetEncoderStack(); }
-  const AudioEncoder* CurrentEncoder() const {
-    return rent_a_codec_.GetEncoderStack();
-  }
-
-  bool CurrentEncoderIsOpus() const { return encoder_is_opus_; }
+  bool CurrentEncoderIsOpus() const;
 
  private:
   rtc::ThreadChecker thread_checker_;
-  CodecInst send_codec_inst_;
-  RentACodec rent_a_codec_;
+  rtc::Optional<CodecInst> send_codec_inst_;
   RentACodec::StackParameters codec_stack_params_;
 
-  bool encoder_is_opus_;
-
   RTC_DISALLOW_COPY_AND_ASSIGN(CodecManager);
 };
 
diff --git a/webrtc/modules/audio_coding/acm2/codec_manager_unittest.cc b/webrtc/modules/audio_coding/acm2/codec_manager_unittest.cc
index c09f256..dce8f38 100644
--- a/webrtc/modules/audio_coding/acm2/codec_manager_unittest.cc
+++ b/webrtc/modules/audio_coding/acm2/codec_manager_unittest.cc
@@ -11,6 +11,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "webrtc/modules/audio_coding/codecs/mock/mock_audio_encoder.h"
 #include "webrtc/modules/audio_coding/acm2/codec_manager.h"
+#include "webrtc/modules/audio_coding/acm2/rent_a_codec.h"
 
 namespace webrtc {
 namespace acm2 {
@@ -46,20 +47,26 @@
   }
 
   CodecManager cm;
-  EXPECT_FALSE(cm.codec_fec_enabled());
-  cm.RegisterEncoder(enc0.get());
-  EXPECT_FALSE(cm.codec_fec_enabled());
+  RentACodec rac;
+  EXPECT_FALSE(cm.GetStackParams()->use_codec_fec);
+  cm.GetStackParams()->speech_encoder = enc0.get();
+  EXPECT_TRUE(rac.RentEncoderStack(cm.GetStackParams()));
+  EXPECT_FALSE(cm.GetStackParams()->use_codec_fec);
   enc0->Mark("A");
-  EXPECT_EQ(0, cm.SetCodecFEC(true));
-  EXPECT_TRUE(cm.codec_fec_enabled());
-  cm.RegisterEncoder(enc1.get());
-  EXPECT_TRUE(cm.codec_fec_enabled());
+  EXPECT_EQ(true, cm.SetCodecFEC(true));
+  EXPECT_TRUE(rac.RentEncoderStack(cm.GetStackParams()));
+  EXPECT_TRUE(cm.GetStackParams()->use_codec_fec);
+  cm.GetStackParams()->speech_encoder = enc1.get();
+  EXPECT_TRUE(rac.RentEncoderStack(cm.GetStackParams()));
+  EXPECT_TRUE(cm.GetStackParams()->use_codec_fec);
 
-  EXPECT_EQ(0, cm.SetCodecFEC(false));
+  EXPECT_EQ(true, cm.SetCodecFEC(false));
+  EXPECT_TRUE(rac.RentEncoderStack(cm.GetStackParams()));
   enc0->Mark("B");
-  EXPECT_FALSE(cm.codec_fec_enabled());
-  cm.RegisterEncoder(enc0.get());
-  EXPECT_FALSE(cm.codec_fec_enabled());
+  EXPECT_FALSE(cm.GetStackParams()->use_codec_fec);
+  cm.GetStackParams()->speech_encoder = enc0.get();
+  EXPECT_TRUE(rac.RentEncoderStack(cm.GetStackParams()));
+  EXPECT_FALSE(cm.GetStackParams()->use_codec_fec);
 }
 
 }  // namespace acm2