Don't recreate the speech encoder if we don't have to

If the specification for the speech encoder hasn't changed, we should
reuse it instead of recreating it. Otherwise, we lose its state. (This
problem was originally discovered because AudioEncoderOpus instances
would forget that they were supposed to be using DTX.)

BUG=webrtc:6020, chromium:622647

Review-Url: https://codereview.webrtc.org/2089183002
Cr-Commit-Position: refs/heads/master@{#13273}

webrtc/modules/audio_coding/codecs/audio_encoder.cc

@@ -60,4 +60,7 @@ void AudioEncoder::SetProjectedPacketLossRate(double fraction) {}
 
 void AudioEncoder::SetTargetBitrate(int target_bps) {}
 
+rtc::ArrayView<std::unique_ptr<AudioEncoder>>
+AudioEncoder::ReclaimContainedEncoders() { return nullptr; }
+
 }  // namespace webrtc

webrtc/modules/audio_coding/codecs/audio_encoder.h

@@ -149,6 +149,15 @@ class AudioEncoder {
   // implementation does the latter).
   virtual void SetTargetBitrate(int target_bps);
 
+  // Causes this encoder to let go of any other encoders it contains, and
+  // returns a pointer to an array where they are stored (which is required to
+  // live as long as this encoder). Unless the returned array is empty, you may
+  // not call any methods on this encoder afterwards, except for the
+  // destructor. The default implementation just returns an empty array.
+  // NOTE: This method is subject to change. Do not call or override it.
+  virtual rtc::ArrayView<std::unique_ptr<AudioEncoder>>
+  ReclaimContainedEncoders();
+
  protected:
   // Subclasses implement this to perform the actual encoding. Called by
   // Encode().

webrtc/modules/audio_coding/codecs/cng/audio_encoder_cng.cc

@@ -187,6 +187,11 @@ void AudioEncoderCng::SetTargetBitrate(int bits_per_second) {
   speech_encoder_->SetTargetBitrate(bits_per_second);
 }
 
+rtc::ArrayView<std::unique_ptr<AudioEncoder>>
+AudioEncoderCng::ReclaimContainedEncoders() {
+  return rtc::ArrayView<std::unique_ptr<AudioEncoder>>(&speech_encoder_, 1);
+}
+
 AudioEncoder::EncodedInfo AudioEncoderCng::EncodePassive(
     size_t frames_to_encode,
     rtc::Buffer* encoded) {

webrtc/modules/audio_coding/codecs/cng/audio_encoder_cng.h

@@ -63,6 +63,8 @@ class AudioEncoderCng final : public AudioEncoder {
   void SetMaxPlaybackRate(int frequency_hz) override;
   void SetProjectedPacketLossRate(double fraction) override;
   void SetTargetBitrate(int target_bps) override;
+  rtc::ArrayView<std::unique_ptr<AudioEncoder>> ReclaimContainedEncoders()
+      override;
 
  private:
   EncodedInfo EncodePassive(size_t frames_to_encode,

webrtc/modules/audio_coding/codecs/red/audio_encoder_copy_red.cc

@@ -123,4 +123,9 @@ void AudioEncoderCopyRed::SetTargetBitrate(int bits_per_second) {
   speech_encoder_->SetTargetBitrate(bits_per_second);
 }
 
+rtc::ArrayView<std::unique_ptr<AudioEncoder>>
+AudioEncoderCopyRed::ReclaimContainedEncoders() {
+  return rtc::ArrayView<std::unique_ptr<AudioEncoder>>(&speech_encoder_, 1);
+}
+
 }  // namespace webrtc

webrtc/modules/audio_coding/codecs/red/audio_encoder_copy_red.h

@@ -51,6 +51,8 @@ class AudioEncoderCopyRed final : public AudioEncoder {
   void SetMaxPlaybackRate(int frequency_hz) override;
   void SetProjectedPacketLossRate(double fraction) override;
   void SetTargetBitrate(int target_bps) override;
+  rtc::ArrayView<std::unique_ptr<AudioEncoder>> ReclaimContainedEncoders()
+      override;
 
  protected:
   EncodedInfo EncodeImpl(uint32_t rtp_timestamp,