[Chromecast] Refactor playout channel selection

Move playout channel selection and mono mixing to StreamMixer to
simplify the logic.

Bug: internal b/118685514
Change-Id: I6c2d871d23958d615c4bf828b5b6013929e3bea0
Reviewed-on: https://chromium-review.googlesource.com/c/1347207Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610991}

chromecast/media/cma/backend/filter_group.cc

@@ -19,15 +19,11 @@ namespace chromecast {
 namespace media {
 
 FilterGroup::FilterGroup(int num_channels,
-                         GroupType type,
                          const std::string& name,
                          std::unique_ptr<PostProcessingPipeline> pipeline,
                          const base::flat_set<std::string>& device_ids,
                          const std::vector<FilterGroup*>& mixed_inputs)
     : num_channels_(num_channels),
-      type_(type),
-      mix_to_mono_(false),
-      playout_channel_(kChannelAll),
       name_(name),
       device_ids_(device_ids),
       mixed_inputs_(mixed_inputs),
@@ -145,19 +141,6 @@ float FilterGroup::MixAndFilter(
     }
   }
 
-  // Copy the active channel to all channels. Only used in the "linearize"
-  // instance.
-  if (playout_channel_ != kChannelAll && type_ == GroupType::kLinearize) {
-    DCHECK_GE(playout_channel_, 0);
-    DCHECK_LT(playout_channel_, num_channels_);
-
-    for (int frame = 0; frame < num_frames; ++frame) {
-      float s = interleaved_.get()[frame * num_channels_ + playout_channel_];
-      for (int c = 0; c < num_channels_; ++c)
-        interleaved_.get()[frame * num_channels_ + c] = s;
-    }
-  }
-
   // Allow paused streams to "ring out" at the last valid volume.
   // If the stream volume is actually 0, this doesn't matter, since the
   // data is 0's anyway.
@@ -174,18 +157,6 @@ float FilterGroup::MixAndFilter(
 
   delay_frames_ = post_processing_pipeline_->ProcessFrames(
       interleaved_.get(), num_frames, last_volume_, is_silence);
-
-  // Mono mixing if needed. Only used in the "Mix" instance.
-  if (mix_to_mono_ && type_ == GroupType::kFinalMix) {
-    for (int frame = 0; frame < num_frames; ++frame) {
-      float sum = 0;
-      for (int c = 0; c < num_channels_; ++c)
-        sum += interleaved_.get()[frame * num_channels_ + c];
-      for (int c = 0; c < num_channels_; ++c)
-        interleaved_.get()[frame * num_channels_ + c] = sum / num_channels_;
-    }
-  }
-
   return last_volume_;
 }
 
@@ -240,18 +211,13 @@ void FilterGroup::SetPostProcessorConfig(const std::string& name,
   post_processing_pipeline_->SetPostProcessorConfig(name, config);
 }
 
-void FilterGroup::SetMixToMono(bool mix_to_mono) {
-  mix_to_mono_ = (num_channels_ != 1 && mix_to_mono);
-}
-
 void FilterGroup::UpdatePlayoutChannel(int playout_channel) {
   if (playout_channel >= num_channels_) {
     LOG(ERROR) << "only " << num_channels_ << " present, wanted channel #"
                << playout_channel;
     return;
   }
-  playout_channel_ = playout_channel;
-  post_processing_pipeline_->UpdatePlayoutChannel(playout_channel_);
+  post_processing_pipeline_->UpdatePlayoutChannel(playout_channel);
 }
 
 }  // namespace media

chromecast/media/cma/backend/filter_group.h

@@ -36,12 +36,8 @@ class PostProcessingPipeline;
 // MixAndFilter() is called (they must be added each time data is queried).
 class FilterGroup {
  public:
-  enum class GroupType { kStream, kFinalMix, kLinearize };
   // |num_channels| indicates number of input audio channels.
   // |type| indicates where in the pipeline this FilterGroup sits.
-  //    some features are specific to certain locations:
-  //     - mono mixer takes place at the end of kFinalMix.
-  //     - channel selection occurs before post-processing in kLinearize.
   // |name| is used for debug printing
   // |pipeline| - processing pipeline.
   // |device_ids| is a set of strings that is used as a filter to determine
@@ -53,7 +49,6 @@ class FilterGroup {
   //   but there is no technical limitation preventing mixing input classes.
 
   FilterGroup(int num_channels,
-              GroupType type,
               const std::string& name,
               std::unique_ptr<PostProcessingPipeline> pipeline,
               const base::flat_set<std::string>& device_ids,
@@ -107,10 +102,7 @@ class FilterGroup {
   void SetPostProcessorConfig(const std::string& name,
                               const std::string& config);
 
-  // Toggles the mono mixer.
-  void SetMixToMono(bool mix_to_mono);
-
-  // Sets the active channel.
+  // Sets the active channel for post processors.
   void UpdatePlayoutChannel(int playout_channel);
 
   // Get content type
@@ -123,9 +115,6 @@ class FilterGroup {
   void AddTempBuffer(int num_channels, int num_frames);
 
   const int num_channels_;
-  const GroupType type_;
-  bool mix_to_mono_;
-  int playout_channel_;
   const std::string name_;
   const base::flat_set<std::string> device_ids_;
   std::vector<FilterGroup*> mixed_inputs_;

chromecast/media/cma/backend/filter_group_unittest.cc

@@ -164,17 +164,14 @@ class FilterGroupTest : public testing::Test {
   ~FilterGroupTest() override {}
 
   void MakeFilterGroup(
-      FilterGroup::GroupType type,
-      bool mix_to_mono,
       std::unique_ptr<MockPostProcessingPipeline> post_processor) {
     post_processor_ = post_processor.get();
     EXPECT_CALL(*post_processor_, SetContentType(kDefaultContentType));
     EXPECT_CALL(*post_processor_, UpdatePlayoutChannel(kDefaultPlayoutChannel));
     filter_group_ = std::make_unique<FilterGroup>(
-        kNumInputChannels, type, "test_filter", std::move(post_processor),
+        kNumInputChannels, "test_filter", std::move(post_processor),
         base::flat_set<std::string>() /* device_ids */,
         std::vector<FilterGroup*>());
-    filter_group_->SetMixToMono(mix_to_mono);
     filter_group_->Initialize(kInputSampleRate);
     filter_group_->AddInput(&input_);
     filter_group_->UpdatePlayoutChannel(kChannelAll);
@@ -210,120 +207,26 @@ class FilterGroupTest : public testing::Test {
 };
 
 TEST_F(FilterGroupTest, Passthrough) {
-  MakeFilterGroup(FilterGroup::GroupType::kFinalMix, false /* mix to mono */,
-                  std::make_unique<NiceMock<MockPostProcessingPipeline>>());
+  MakeFilterGroup(std::make_unique<NiceMock<MockPostProcessingPipeline>>());
   EXPECT_CALL(*post_processor_, ProcessFrames(_, kInputFrames, _, false));
 
   filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
   AssertPassthrough();
 }
 
-TEST_F(FilterGroupTest, StreamGroupsDoNotMonoMix) {
-  MakeFilterGroup(FilterGroup::GroupType::kStream, true /* mix to mono */,
-                  std::make_unique<NiceMock<MockPostProcessingPipeline>>());
-  EXPECT_CALL(*post_processor_, ProcessFrames(_, kInputFrames, _, false));
-
-  filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-  AssertPassthrough();
-}
-
-TEST_F(FilterGroupTest, LinearizeGroupsDoNotMonoMix) {
-  MakeFilterGroup(FilterGroup::GroupType::kLinearize, true /* mix to mono */,
-                  std::make_unique<NiceMock<MockPostProcessingPipeline>>());
-  EXPECT_CALL(*post_processor_, ProcessFrames(_, kInputFrames, _, false));
-
-  filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-  AssertPassthrough();
-}
-
-TEST_F(FilterGroupTest, MonoMixer) {
-  MakeFilterGroup(FilterGroup::GroupType::kFinalMix, true /* mix to mono */,
-                  std::make_unique<NiceMock<MockPostProcessingPipeline>>());
-  filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-
-  // Verify if the fiter group output matches the source after down mixing.
-  float* interleaved_data = filter_group_->GetOutputBuffer();
-  for (int i = 0; i < kInputFrames; ++i) {
-    ASSERT_EQ((LeftInput(i) + RightInput(i)) / 2, interleaved_data[i * 2]);
-    ASSERT_EQ(interleaved_data[i * 2], interleaved_data[i * 2 + 1]);
-  }
-}
-
-TEST_F(FilterGroupTest, MonoMixesAfterPostProcessors) {
-  MakeFilterGroup(FilterGroup::GroupType::kFinalMix, true /* mix to mono */,
-                  std::make_unique<NiceMock<InvertChannelPostProcessor>>(
-                      kNumInputChannels, 0));
-  filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-
-  // Verify both output channels = (-1 * ch0 + ch1) / 2 after mixing.
-  // If order of mixing, filtering is incorrect, the channels won't match.
-  float* interleaved_data = filter_group_->GetOutputBuffer();
-  for (int i = 0; i < kInputFrames; ++i) {
-    ASSERT_EQ((-LeftInput(i) + RightInput(i)) / 2, interleaved_data[i * 2]);
-    ASSERT_EQ(interleaved_data[i * 2], interleaved_data[i * 2 + 1]);
-  }
-}
-
-TEST_F(FilterGroupTest, StreamGroupDoesNotSelectChannels) {
-  MakeFilterGroup(FilterGroup::GroupType::kStream, false /* mix to mono */,
-                  std::make_unique<NiceMock<MockPostProcessingPipeline>>());
-
-  EXPECT_CALL(*post_processor_, UpdatePlayoutChannel(0));
-  filter_group_->UpdatePlayoutChannel(0);
-  filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-  AssertPassthrough();
-
-  source_.SetData(GetTestData());
-  EXPECT_CALL(*post_processor_, UpdatePlayoutChannel(1));
-  filter_group_->UpdatePlayoutChannel(1);
-  filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-  AssertPassthrough();
-}
-
-TEST_F(FilterGroupTest, MixGroupDoesNotSelectChannels) {
-  MakeFilterGroup(FilterGroup::GroupType::kFinalMix, false /* mix to mono */,
-                  std::make_unique<NiceMock<MockPostProcessingPipeline>>());
-
-  EXPECT_CALL(*post_processor_, UpdatePlayoutChannel(0));
-  filter_group_->UpdatePlayoutChannel(0);
-  filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-  AssertPassthrough();
-
-  source_.SetData(GetTestData());
-  EXPECT_CALL(*post_processor_, UpdatePlayoutChannel(1));
-  filter_group_->UpdatePlayoutChannel(1);
-  filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-  AssertPassthrough();
-}
-
 TEST_F(FilterGroupTest, SelectsOutputChannel) {
-  MakeFilterGroup(FilterGroup::GroupType::kLinearize, false /* mix to mono */,
-                  std::make_unique<NiceMock<MockPostProcessingPipeline>>());
+  MakeFilterGroup(std::make_unique<NiceMock<MockPostProcessingPipeline>>());
 
   EXPECT_CALL(*post_processor_, UpdatePlayoutChannel(0));
   filter_group_->UpdatePlayoutChannel(0);
   filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
 
-  float* interleaved_data = filter_group_->GetOutputBuffer();
-  for (int f = 0; f < kInputFrames; ++f) {
-    for (int ch = 0; ch < kNumInputChannels; ++ch) {
-      // Both output channels should be equal to left channel.
-      ASSERT_EQ(interleaved_data[f * kNumInputChannels + ch], LeftInput(f));
-    }
-  }
-
   testing::Mock::VerifyAndClearExpectations(post_processor_);
   source_.SetData(GetTestData());
 
   EXPECT_CALL(*post_processor_, UpdatePlayoutChannel(1));
   filter_group_->UpdatePlayoutChannel(1);
   filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-  for (int f = 0; f < kInputFrames; ++f) {
-    for (int ch = 0; ch < kNumInputChannels; ++ch) {
-      // Both output channels should be equal to right channel.
-      ASSERT_EQ(interleaved_data[f * kNumInputChannels + ch], RightInput(f));
-    }
-  }
 
   testing::Mock::VerifyAndClearExpectations(post_processor_);
   source_.SetData(GetTestData());
@@ -331,35 +234,10 @@ TEST_F(FilterGroupTest, SelectsOutputChannel) {
   EXPECT_CALL(*post_processor_, UpdatePlayoutChannel(-1));
   filter_group_->UpdatePlayoutChannel(-1);
   filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-  for (int f = 0; f < kInputFrames; ++f) {
-    for (int ch = 0; ch < kNumInputChannels; ++ch) {
-      // Back to normal (passthrough).
-      ASSERT_EQ(interleaved_data[f * kNumInputChannels + ch], Input(ch, f));
-    }
-  }
-}
-
-TEST_F(FilterGroupTest, SelectsOutputChannelBeforePostProcessors) {
-  MakeFilterGroup(FilterGroup::GroupType::kLinearize, false /* mix to mono */,
-                  std::make_unique<NiceMock<InvertChannelPostProcessor>>(
-                      kNumInputChannels, 0));
-  EXPECT_CALL(*post_processor_, UpdatePlayoutChannel(0));
-  filter_group_->UpdatePlayoutChannel(0);
-  filter_group_->MixAndFilter(kInputFrames, RenderingDelay());
-
-  float* interleaved_data = filter_group_->GetOutputBuffer();
-  for (int f = 0; f < kInputFrames; ++f) {
-    // channel 0 out = channel 0 in * -1
-    // channel 1 out = channel 0 in
-    // (If order is wrong, both channels will be channel_0_in * -1).
-    ASSERT_EQ(interleaved_data[f * kNumInputChannels], LeftInput(f) * -1);
-    ASSERT_EQ(interleaved_data[f * kNumInputChannels + 1], LeftInput(f));
-  }
 }
 
 TEST_F(FilterGroupTest, ChecksContentType) {
-  MakeFilterGroup(FilterGroup::GroupType::kStream, false,
-                  std::make_unique<NiceMock<MockPostProcessingPipeline>>());
+  MakeFilterGroup(std::make_unique<NiceMock<MockPostProcessingPipeline>>());
 
   NiceMock<MockMixerSource> tts_source(kInputSampleRate);
   tts_source.set_content_type(AudioContentType::kCommunication);
@@ -404,8 +282,7 @@ TEST_F(FilterGroupTest, ChecksContentType) {
 
 TEST_F(FilterGroupTest, ReportsOutputChannels) {
   const int num_output_channels = 4;
-  MakeFilterGroup(FilterGroup::GroupType::kStream, false,
-                  std::make_unique<NiceMock<MockPostProcessingPipeline>>(
+  MakeFilterGroup(std::make_unique<NiceMock<MockPostProcessingPipeline>>(
       num_output_channels));
 
   EXPECT_EQ(num_output_channels, filter_group_->GetOutputChannelCount());

chromecast/media/cma/backend/mixer_pipeline.cc

@@ -30,7 +30,6 @@ bool IsOutputDeviceId(const std::string& device) {
 }
 
 std::unique_ptr<FilterGroup> CreateFilterGroup(
-    FilterGroup::GroupType type,
     int input_channels,
     const std::string& name,
     const base::ListValue* filter_list,
@@ -40,9 +39,8 @@ std::unique_ptr<FilterGroup> CreateFilterGroup(
   DCHECK(ppp_factory);
   auto pipeline =
       ppp_factory->CreatePipeline(name, filter_list, input_channels);
-  return std::make_unique<FilterGroup>(input_channels, type, name,
-                                       std::move(pipeline), device_ids,
-                                       mixed_inputs);
+  return std::make_unique<FilterGroup>(
+      input_channels, name, std::move(pipeline), device_ids, mixed_inputs);
 }
 
 }  // namespace
@@ -83,8 +81,8 @@ bool MixerPipeline::BuildPipeline(PostProcessingPipelineParser* config,
         return false;
       }
       filter_groups_.push_back(CreateFilterGroup(
-          FilterGroup::GroupType::kStream, kNumInputChannels,
-          *device_ids.begin() /* name */, stream_pipeline.pipeline, device_ids,
+          kNumInputChannels, *device_ids.begin() /* name */,
+          stream_pipeline.pipeline, device_ids,
           std::vector<FilterGroup*>() /* mixed_inputs */, factory));
       if (device_ids.find(::media::AudioDeviceDescription::kDefaultDeviceId) !=
           device_ids.end()) {
@@ -110,8 +108,7 @@ bool MixerPipeline::BuildPipeline(PostProcessingPipelineParser* config,
     }
 
     filter_groups_.push_back(CreateFilterGroup(
-        FilterGroup::GroupType::kFinalMix, mix_group_input_channels, "mix",
-        config->GetMixPipeline(),
+        mix_group_input_channels, "mix", config->GetMixPipeline(),
         base::flat_set<std::string>() /* device_ids */, filter_group_ptrs,
         factory));
   } else {
@@ -119,8 +116,7 @@ bool MixerPipeline::BuildPipeline(PostProcessingPipelineParser* config,
     std::string kDefaultDeviceId =
         ::media::AudioDeviceDescription::kDefaultDeviceId;
     filter_groups_.push_back(CreateFilterGroup(
-        FilterGroup::GroupType::kFinalMix, kNumInputChannels, "mix",
-        config->GetMixPipeline(),
+        kNumInputChannels, "mix", config->GetMixPipeline(),
         base::flat_set<std::string>({kDefaultDeviceId}),
         std::vector<FilterGroup*>() /* mixed_inputs */, factory));
     default_stream_group_ = filter_groups_.back().get();
@@ -129,7 +125,6 @@ bool MixerPipeline::BuildPipeline(PostProcessingPipelineParser* config,
   loopback_output_group_ = filter_groups_.back().get();
 
   filter_groups_.push_back(CreateFilterGroup(
-      FilterGroup::GroupType::kLinearize,
       loopback_output_group_->GetOutputChannelCount(), "linearize",
       config->GetLinearizePipeline(),
       base::flat_set<std::string>() /* device_ids */,
@@ -206,10 +201,6 @@ void MixerPipeline::SetPostProcessorConfig(const std::string& name,
   }
 }
 
-void MixerPipeline::SetMixToMono(bool mix_to_mono) {
-  loopback_output_group_->SetMixToMono(mix_to_mono);
-}
-
 void MixerPipeline::SetPlayoutChannel(int playout_channel) {
   for (auto& filter_group : filter_groups_) {
     filter_group->UpdatePlayoutChannel(playout_channel);

chromecast/media/cma/backend/mixer_pipeline.h

@@ -70,9 +70,6 @@ class MixerPipeline {
   // and GetOutput(), i.e. the group delay of PostProcessors in "linearize"
   int64_t GetPostLoopbackRenderingDelayMicroseconds() const;
 
-  // Informs FilterGroups that the output should be mixed to mono.
-  void SetMixToMono(bool mix_to_mono);
-
   // Informs FilterGroups and PostProcessors which channel will be played out.
   // |playout_channel| may be |-1| to signal all channels will be played out.
   void SetPlayoutChannel(int playout_channel);

chromecast/media/cma/backend/stream_mixer.cc

@@ -230,6 +230,7 @@ StreamMixer::StreamMixer(
 
   CreatePostProcessors([](bool, const std::string&) {},
                        "" /* override_config */);
+  mixer_pipeline_->SetPlayoutChannel(playout_channel_);
 
   // TODO(jyw): command line flag for filter frame alignment.
   DCHECK_EQ(filter_frame_alignment_ & (filter_frame_alignment_ - 1), 0)
@@ -580,14 +581,15 @@ void StreamMixer::UpdatePlayoutChannel() {
           std::min(it.second->source()->playout_channel(), playout_channel);
     }
   }
+  if (playout_channel == playout_channel_) {
+    return;
+  }
 
   DCHECK(playout_channel == kChannelAll ||
          playout_channel >= 0 && playout_channel < kNumInputChannels);
   LOG(INFO) << "Update playout channel: " << playout_channel;
-
-  mixer_pipeline_->SetMixToMono(num_output_channels_ == 1 &&
-                                playout_channel == kChannelAll);
-  mixer_pipeline_->SetPlayoutChannel(playout_channel);
+  playout_channel_ = playout_channel;
+  mixer_pipeline_->SetPlayoutChannel(playout_channel_);
 }
 
 MediaPipelineBackend::AudioDecoder::RenderingDelay
@@ -655,13 +657,7 @@ void StreamMixer::WriteMixedPcm(int frames, int64_t expected_playback_time) {
 
   float* mixed_data = mixer_pipeline_->GetLoopbackOutput();
   if (num_output_channels_ == 1 && mix_channel_count != 1) {
-    for (int i = 0; i < frames; ++i) {
-      float sum = 0;
-      for (int c = 0; c < mix_channel_count; ++c) {
-        sum += mixed_data[i * mix_channel_count + c];
-      }
-      mixed_data[i] = sum / mix_channel_count;
-    }
+    MixToMono(mixed_data, frames, mix_channel_count);
     loopback_channel_count = 1;
   }
 
@@ -685,8 +681,14 @@ void StreamMixer::WriteMixedPcm(int frames, int64_t expected_playback_time) {
   float* linearized_data = mixer_pipeline_->GetOutput();
   int linearize_channel_count = mixer_pipeline_->GetOutputChannelCount();
   if (num_output_channels_ == 1 && linearize_channel_count != 1) {
-    for (int i = 0; i < frames; ++i) {
-      linearized_data[i] = linearized_data[i * linearize_channel_count];
+    MixToMono(linearized_data, frames, linearize_channel_count);
+  } else if (num_output_channels_ > 1 && playout_channel_ != kChannelAll) {
+    // Duplicate selected channel to all channels.
+    for (int f = 0; f < frames; ++f) {
+      float selected =
+          linearized_data[f * num_output_channels_ + playout_channel_];
+      for (int c = 0; c < num_output_channels_; ++c)
+        linearized_data[f * num_output_channels_ + c] = selected;
     }
   }
 
@@ -704,6 +706,23 @@ void StreamMixer::WriteMixedPcm(int frames, int64_t expected_playback_time) {
   }
 }
 
+void StreamMixer::MixToMono(float* data, int frames, int channels) {
+  DCHECK_EQ(num_output_channels_, 1);
+  if (playout_channel_ == kChannelAll) {
+    for (int i = 0; i < frames; ++i) {
+      float sum = 0;
+      for (int c = 0; c < channels; ++c) {
+        sum += data[i * channels + c];
+      }
+      data[i] = sum / channels;
+    }
+  } else {
+    for (int i = 0; i < frames; ++i) {
+      data[i] = data[i * channels + playout_channel_];
+    }
+  }
+}
+
 void StreamMixer::AddLoopbackAudioObserver(
     CastMediaShlib::LoopbackAudioObserver* observer) {
   VLOG(1) << __func__;

chromecast/media/cma/backend/stream_mixer.h

@@ -176,6 +176,7 @@ class StreamMixer {
   void PlaybackLoop();
   void WriteOneBuffer();
   void WriteMixedPcm(int frames, int64_t expected_playback_time);
+  void MixToMono(float* data, int frames, int channels);
 
   void SetVolumeOnThread(AudioContentType type, float level);
   void SetMutedOnThread(AudioContentType type, bool muted);
@@ -235,6 +236,7 @@ class StreamMixer {
   // AudioPostProcessors require stricter alignment conditions.
   const int filter_frame_alignment_;
 
+  int playout_channel_ = kChannelAll;
   int requested_output_samples_per_second_ = 0;
   int output_samples_per_second_ = 0;
   int frames_per_write_ = 0;

chromecast/media/cma/backend/stream_mixer_unittest.cc

@@ -955,7 +955,7 @@ TEST_F(StreamMixerTest, PicksPlayoutChannel) {
   VerifyAndClearPostProcessors(factory_ptr);
 
   // Requests: all = 0 ch0 = 0 ch1 = 2.
-  EXPECT_CALL_ALL_POSTPROCESSORS(factory_ptr, UpdatePlayoutChannel(1));
+  // Playout channel is still 1.
   mixer_->AddInput(&input4);
   WaitForMixer();
   VerifyAndClearPostProcessors(factory_ptr);
@@ -969,8 +969,7 @@ TEST_F(StreamMixerTest, PicksPlayoutChannel) {
   VerifyAndClearPostProcessors(factory_ptr);
 
   // Requests: all = 1 ch0 = 0 ch1 = 1.
-  EXPECT_CALL_ALL_POSTPROCESSORS(factory_ptr,
-                                 UpdatePlayoutChannel(kChannelAll));
+  // Playout channel is still 'all'.
   mixer_->RemoveInput(&input3);
   WaitForMixer();
   VerifyAndClearPostProcessors(factory_ptr);