diff --git a/src/engine/audio/audio_mixer.cc b/src/engine/audio/audio_mixer.cc
index f9a7ff3..ac8c27b 100644
--- a/src/engine/audio/audio_mixer.cc
+++ b/src/engine/audio/audio_mixer.cc
@@ -4,7 +4,6 @@
 
 #include "base/log.h"
 #include "base/task_runner.h"
-#include "base/thread_pool.h"
 #include "engine/audio/audio_bus.h"
 #include "engine/audio/mixer_input.h"
 
@@ -33,11 +32,11 @@ AudioMixer::~AudioMixer() {
   audio_sink_.reset();
 }
 
-void AudioMixer::AddInput(std::shared_ptr<MixerInput> input) {
+void AudioMixer::AddInput(std::shared_ptr<MixerInput> mixer_input) {
   DCHECK(audio_enabled_);
 
   std::lock_guard<std::mutex> scoped_lock(lock_);
-  inputs_[0].push_back(input);
+  inputs_[0].push_back(mixer_input);
 }
 
 void AudioMixer::Suspend() {
@@ -62,8 +61,8 @@ void AudioMixer::RenderAudio(float* output_buffer, size_t num_frames) {
   memset(output_buffer, 0, sizeof(float) * num_frames * kChannelCount);
 
   for (auto it = inputs_[1].begin(); it != inputs_[1].end();) {
-    auto audio_bus = (*it)->audio_bus.get();
-    unsigned flags = (*it)->flags.load(std::memory_order_relaxed);
+    auto* audio_bus = (*it)->GetAudioBus().get();
+    unsigned flags = (*it)->GetFlags();
     bool marked_for_removal = false;
 
     if (flags & MixerInput::kStopped) {
@@ -75,14 +74,12 @@ void AudioMixer::RenderAudio(float* output_buffer, size_t num_frames) {
         src[1] = src[0];  // mono.
 
       size_t num_samples = audio_bus->samples_per_channel();
-      size_t src_index = (*it)->src_index;
-      size_t step = (*it)->step.load(std::memory_order_relaxed);
-      size_t accumulator = (*it)->accumulator;
-      float amplitude = (*it)->amplitude;
-      float amplitude_inc =
-          (*it)->amplitude_inc.load(std::memory_order_relaxed);
-      float max_amplitude =
-          (*it)->max_amplitude.load(std::memory_order_relaxed);
+      size_t src_index = (*it)->GetSrcIndex();
+      size_t step = (*it)->GetStep();
+      size_t accumulator = (*it)->GetAccumulator();
+      float amplitude = (*it)->GetAmplitude();
+      float amplitude_inc = (*it)->GetAmplitudeInc();
+      float max_amplitude = (*it)->GetMaxAmplitude();
       size_t channel_offset = (flags & MixerInput::kSimulateStereo)
                                   ? audio_bus->sample_rate() / 10
                                   : 0;
@@ -118,37 +115,29 @@ void AudioMixer::RenderAudio(float* output_buffer, size_t num_frames) {
           accumulator %= 100;
         } else {
           if (audio_bus->EndOfStream()) {
-            src_index %= num_samples;
-            marked_for_removal = !(flags & MixerInput::kLoop);
+            if (!(flags & MixerInput::kLoop))
+              marked_for_removal = true;
+            else
+              src_index %= num_samples;
             break;
           }
 
-          if (!(*it)->streaming_in_progress.load(std::memory_order_acquire)) {
+          if ((*it)->OnMoreData(!!(flags & MixerInput::kLoop))) {
             src_index %= num_samples;
-            (*it)->streaming_in_progress.store(true, std::memory_order_relaxed);
-
-            // Swap buffers and start streaming in background.
-            audio_bus->SwapBuffers();
             src[0] = audio_bus->GetChannelData(0);
             src[1] = audio_bus->GetChannelData(1);
             if (!src[1])
               src[1] = src[0];  // mono.
             num_samples = audio_bus->samples_per_channel();
-
-            ThreadPool::Get().PostTask(
-                HERE,
-                std::bind(&AudioMixer::DoStream, this, *it,
-                          flags & MixerInput::kLoop),
-                true);
           } else {
             DLOG(0) << "Mixer buffer underrun!";
           }
         }
       }
 
-      (*it)->src_index = src_index;
-      (*it)->accumulator = accumulator;
-      (*it)->amplitude = amplitude;
+      // Remember last sample position and volume.
+      (*it)->SetPosition(src_index, accumulator);
+      (*it)->SetAmplitude(amplitude);
     }
 
     if (marked_for_removal) {
@@ -160,9 +149,9 @@ void AudioMixer::RenderAudio(float* output_buffer, size_t num_frames) {
   }
 
   for (auto it = removed_inputs_.begin(); it != removed_inputs_.end();) {
-    if (!(*it)->streaming_in_progress.load(std::memory_order_relaxed)) {
+    if (!(*it)->IsStreamingInProgress()) {
       main_thread_task_runner_->PostTask(
-          HERE, std::bind(&AudioMixer::EndCallback, this, *it));
+          HERE, std::bind(&MixerInput::OnRemovedFromMixer, *it));
       it = removed_inputs_.erase(it);
     } else {
       ++it;
@@ -170,25 +159,4 @@ void AudioMixer::RenderAudio(float* output_buffer, size_t num_frames) {
   }
 }
 
-void AudioMixer::DoStream(std::shared_ptr<MixerInput> input, bool loop) {
-  input->audio_bus->Stream(loop);
-  input->streaming_in_progress.store(false, std::memory_order_release);
-}
-
-void AudioMixer::EndCallback(std::shared_ptr<MixerInput> input) {
-  input->streaming = false;
-
-  if (input->pending_audio_bus) {
-    input->audio_bus = input->pending_audio_bus;
-    input->pending_audio_bus.reset();
-  }
-
-  if (input->end_cb)
-    input->end_cb();
-  if (input->restart_cb) {
-    input->restart_cb();
-    input->restart_cb = nullptr;
-  }
-}
-
 }  // namespace eng
diff --git a/src/engine/audio/audio_mixer.h b/src/engine/audio/audio_mixer.h
index f86a721..a2f424a 100644
--- a/src/engine/audio/audio_mixer.h
+++ b/src/engine/audio/audio_mixer.h
@@ -14,8 +14,7 @@ class TaskRunner;
 
 namespace eng {
 
-class AudioBus;
-struct MixerInput;
+class MixerInput;
 
 // Mix and render audio with low overhead. The mixer has zero or more inputs
 // which can be added at any time. The mixer will pull from each input source
@@ -29,7 +28,7 @@ class AudioMixer : public AudioSink::Delegate {
   AudioMixer();
   ~AudioMixer();
 
-  void AddInput(std::shared_ptr<MixerInput> input);
+  void AddInput(std::shared_ptr<MixerInput> mixer_input);
 
   void SetEnableAudio(bool enable) { audio_enabled_ = enable; }
   bool IsAudioEnabled() const { return audio_enabled_; }
@@ -57,10 +56,6 @@ class AudioMixer : public AudioSink::Delegate {
   int GetChannelCount() final { return kChannelCount; }
   void RenderAudio(float* output_buffer, size_t num_frames) final;
 
-  void DoStream(std::shared_ptr<MixerInput> sample, bool loop);
-
-  void EndCallback(std::shared_ptr<MixerInput> sample);
-
   AudioMixer(const AudioMixer&) = delete;
   AudioMixer& operator=(const AudioMixer&) = delete;
 };
diff --git a/src/engine/audio/mixer_input.cc b/src/engine/audio/mixer_input.cc
index 98c940c..7873bad 100644
--- a/src/engine/audio/mixer_input.cc
+++ b/src/engine/audio/mixer_input.cc
@@ -1,6 +1,7 @@
 #include "engine/audio/mixer_input.h"
 
 #include "base/log.h"
+#include "base/thread_pool.h"
 #include "engine/audio/audio_bus.h"
 #include "engine/audio/audio_mixer.h"
 
@@ -21,78 +22,124 @@ std::shared_ptr<MixerInput> MixerInput::Create() {
   return std::shared_ptr<MixerInput>(new MixerInput());
 }
 
-void MixerInput::SetAudioBus(std::shared_ptr<AudioBus> bus) {
-  if (streaming)
-    pending_audio_bus = bus;
+void MixerInput::SetAudioBus(std::shared_ptr<AudioBus> audio_bus) {
+  if (playing_)
+    pending_audio_bus_ = audio_bus;
   else
-    audio_bus = bus;
+    audio_bus_ = audio_bus;
 }
 
 void MixerInput::Play(AudioMixer* mixer, bool restart) {
-  if (!mixer->IsAudioEnabled())
+  if (!mixer->IsAudioEnabled()) {
+    if (!playing_ && end_cb_)
+      end_cb_();
     return;
+  }
 
-  // If already streaming check if stream position needs to be reset.
-  if (streaming) {
+  // If already playing check if stream position needs to be reset.
+  if (playing_) {
     if (restart)
-      flags.fetch_or(kStopped, std::memory_order_relaxed);
+      flags_.fetch_or(kStopped, std::memory_order_relaxed);
 
-    if (flags.load(std::memory_order_relaxed) & kStopped)
-      restart_cb = [&, mixer, restart]() -> void { Play(mixer, restart); };
+    if (flags_.load(std::memory_order_relaxed) & kStopped)
+      restart_cb_ = [&, mixer, restart]() -> void { Play(mixer, restart); };
 
     return;
   }
 
-  if (restart || audio_bus->EndOfStream()) {
-    src_index = 0;
-    accumulator = 0;
-    audio_bus->ResetStream();
+  if (restart || audio_bus_->EndOfStream()) {
+    src_index_ = 0;
+    accumulator_ = 0;
+    audio_bus_->ResetStream();
   }
 
-  streaming = true;
-  flags.fetch_and(~kStopped, std::memory_order_relaxed);
+  playing_ = true;
+  flags_.fetch_and(~kStopped, std::memory_order_relaxed);
   mixer->AddInput(shared_from_this());
 }
 
 void MixerInput::Stop() {
-  if (streaming) {
-    restart_cb = nullptr;
-    flags.fetch_or(kStopped, std::memory_order_relaxed);
+  if (playing_) {
+    restart_cb_ = nullptr;
+    flags_.fetch_or(kStopped, std::memory_order_relaxed);
   }
 }
 
 void MixerInput::SetLoop(bool loop) {
   if (loop)
-    flags.fetch_or(kLoop, std::memory_order_relaxed);
+    flags_.fetch_or(kLoop, std::memory_order_relaxed);
   else
-    flags.fetch_and(~kLoop, std::memory_order_relaxed);
+    flags_.fetch_and(~kLoop, std::memory_order_relaxed);
 }
 
 void MixerInput::SetSimulateStereo(bool simulate) {
   if (simulate)
-    flags.fetch_or(kSimulateStereo, std::memory_order_relaxed);
+    flags_.fetch_or(kSimulateStereo, std::memory_order_relaxed);
   else
-    flags.fetch_and(~kSimulateStereo, std::memory_order_relaxed);
+    flags_.fetch_and(~kSimulateStereo, std::memory_order_relaxed);
 }
 
 void MixerInput::SetResampleStep(size_t value) {
-  step.store(value + 100, std::memory_order_relaxed);
+  step_.store(value + 100, std::memory_order_relaxed);
 }
 
 void MixerInput::SetAmplitude(float value) {
-  amplitude.store(value, std::memory_order_relaxed);
+  amplitude_.store(value, std::memory_order_relaxed);
 }
 
 void MixerInput::SetMaxAmplitude(float value) {
-  max_amplitude.store(value, std::memory_order_relaxed);
+  max_amplitude_.store(value, std::memory_order_relaxed);
 }
 
 void MixerInput::SetAmplitudeInc(float value) {
-  amplitude_inc.store(value, std::memory_order_relaxed);
+  amplitude_inc_.store(value, std::memory_order_relaxed);
 }
 
 void MixerInput::SetEndCallback(base::Closure cb) {
-  end_cb = std::move(cb);
+  end_cb_ = std::move(cb);
+}
+
+bool MixerInput::IsStreamingInProgress() const {
+  return streaming_in_progress_.load(std::memory_order_relaxed);
+}
+
+void MixerInput::SetPosition(size_t index, int accumulator) {
+  src_index_ = index;
+  accumulator_ = accumulator;
+}
+
+bool MixerInput::OnMoreData(bool loop) {
+  if (streaming_in_progress_.load(std::memory_order_acquire))
+    return false;
+
+  streaming_in_progress_.store(true, std::memory_order_relaxed);
+  audio_bus_->SwapBuffers();
+  ThreadPool::Get().PostTask(
+      HERE,
+      [&, loop]() {
+        audio_bus_->Stream(loop);
+        streaming_in_progress_.store(false, std::memory_order_release);
+      },
+      true);
+  return true;
+}
+
+void MixerInput::OnRemovedFromMixer() {
+  DCHECK(!streaming_in_progress_.load(std::memory_order_relaxed));
+  DCHECK(playing_);
+  playing_ = false;
+
+  if (pending_audio_bus_) {
+    audio_bus_ = pending_audio_bus_;
+    pending_audio_bus_.reset();
+  }
+
+  if (end_cb_)
+    end_cb_();
+  if (restart_cb_) {
+    restart_cb_();
+    restart_cb_ = nullptr;
+  }
 }
 
 }  // namespace eng
diff --git a/src/engine/audio/mixer_input.h b/src/engine/audio/mixer_input.h
index 8920fde..22b7a6a 100644
--- a/src/engine/audio/mixer_input.h
+++ b/src/engine/audio/mixer_input.h
@@ -13,16 +13,19 @@ class AudioMixer;
 
 // An audio input stream that gets mixed and rendered to the audio sink. Handles
 // playback and volume control.
-struct MixerInput : public std::enable_shared_from_this<MixerInput> {
+class MixerInput : public std::enable_shared_from_this<MixerInput> {
+ public:
   enum Flags { kLoop = 1, kStopped = 2, kSimulateStereo = 4 };
 
   ~MixerInput();
 
   static std::shared_ptr<MixerInput> Create();
 
-  // Set AudioBus for playback. If this MixerInput is already streaming, keeps
-  // it as pending and sets once playback ends.
-  void SetAudioBus(std::shared_ptr<AudioBus> bus);
+  bool IsValid() const { return !!audio_bus_; }
+
+  // Set AudioBus for playback. If this MixerInput is already playing, keeps it
+  // as pending and sets once playback ends.
+  void SetAudioBus(std::shared_ptr<AudioBus> audio_bus);
 
   // Starts playback. Remembers last stream position. Resets the stream position
   // if restart is true.
@@ -31,6 +34,7 @@ struct MixerInput : public std::enable_shared_from_this<MixerInput> {
   // Stops playback. Does not reset stream position.
   void Stop();
 
+  // Set whether the playback should loop or not.
   void SetLoop(bool loop);
 
   // Simulate stereo effect slightly delays one channel.
@@ -47,30 +51,57 @@ struct MixerInput : public std::enable_shared_from_this<MixerInput> {
   // Set a callback to be called once playback ends.
   void SetEndCallback(base::Closure cb);
 
-  // Active AudioBus.
-  std::shared_ptr<AudioBus> audio_bus;
-  // AudioBus to be set as active once playback ends.
-  std::shared_ptr<AudioBus> pending_audio_bus;
-  // Stream position.
-  size_t src_index = 0;
-  size_t accumulator = 0;
+  // Getters
+  std::shared_ptr<AudioBus> GetAudioBus() const { return audio_bus_; }
+  unsigned GetFlags() const { return flags_.load(std::memory_order_relaxed); }
+  size_t GetStep() const { return step_.load(std::memory_order_relaxed); }
+  float GetAmplitude() const {
+    return amplitude_.load(std::memory_order_relaxed);
+  }
+  float GetAmplitudeInc() const {
+    return amplitude_inc_.load(std::memory_order_relaxed);
+  }
+  float GetMaxAmplitude() const {
+    return max_amplitude_.load(std::memory_order_relaxed);
+  }
+  size_t GetSrcIndex() const { return src_index_; }
+  size_t GetAccumulator() const { return accumulator_; }
 
-  // Accessed by main thread only.
-  bool streaming = false;
-  base::Closure end_cb;
-  base::Closure restart_cb;
+  bool IsStreamingInProgress() const;
 
-  // Accessed by main thread and audio thread.
-  std::atomic<unsigned> flags{0};
-  std::atomic<size_t> step{100};
-  std::atomic<float> amplitude{1.0f};
-  std::atomic<float> amplitude_inc{0};
-  std::atomic<float> max_amplitude{1.0f};
+  // Called by the mixer to save the last sample position.
+  void SetPosition(size_t index, int accumulator);
 
-  // Accessed by audio thread and decoding worker thread.
-  std::atomic<bool> streaming_in_progress{false};
+  // Called by the mixer when more data is needed.
+  bool OnMoreData(bool loop);
+
+  // Called by the mixer when playback ends.
+  void OnRemovedFromMixer();
 
  private:
+  // Active AudioBus.
+  std::shared_ptr<AudioBus> audio_bus_;
+  // AudioBus to be set as active once playback ends.
+  std::shared_ptr<AudioBus> pending_audio_bus_;
+  // Stream position.
+  size_t src_index_ = 0;
+  size_t accumulator_ = 0;
+
+  // Accessed by main thread only.
+  bool playing_ = false;
+  base::Closure end_cb_;
+  base::Closure restart_cb_;
+
+  // Accessed by main thread and audio thread.
+  std::atomic<unsigned> flags_{0};
+  std::atomic<size_t> step_{100};
+  std::atomic<float> amplitude_{1.0f};
+  std::atomic<float> amplitude_inc_{0};
+  std::atomic<float> max_amplitude_{1.0f};
+
+  // Accessed by audio thread and decoding worker thread.
+  std::atomic<bool> streaming_in_progress_{false};
+
   MixerInput();
 };
 
diff --git a/src/engine/sound_player.cc b/src/engine/sound_player.cc
index 51b536b..ad6a18b 100644
--- a/src/engine/sound_player.cc
+++ b/src/engine/sound_player.cc
@@ -26,7 +26,7 @@ void SoundPlayer::SetSound(std::shared_ptr<AudioBus> sound) {
 }
 
 void SoundPlayer::Play(bool loop, float fade_in_duration) {
-  if (!input_->audio_bus)
+  if (!input_->IsValid())
     return;
 
   int step = variate_ ? Engine::Get().GetRandomGenerator().Roll(3) - 2 : 0;
@@ -35,7 +35,7 @@ void SoundPlayer::Play(bool loop, float fade_in_duration) {
   if (fade_in_duration > 0) {
     input_->SetAmplitude(0);
     input_->SetAmplitudeInc(
-        1.0f / (input_->audio_bus->sample_rate() * fade_in_duration));
+        1.0f / (input_->GetAudioBus()->sample_rate() * fade_in_duration));
   } else {
     input_->SetAmplitude(max_amplitude_);
     input_->SetAmplitudeInc(0);
@@ -44,24 +44,24 @@ void SoundPlayer::Play(bool loop, float fade_in_duration) {
 }
 
 void SoundPlayer::Resume(float fade_in_duration) {
-  if (!input_->audio_bus)
+  if (!input_->IsValid())
     return;
 
   if (fade_in_duration > 0) {
     input_->SetAmplitude(0);
     input_->SetAmplitudeInc(
-        1.0f / (input_->audio_bus->sample_rate() * fade_in_duration));
+        1.0f / (input_->GetAudioBus()->sample_rate() * fade_in_duration));
   }
   input_->Play(Engine::Get().GetAudioMixer(), false);
 }
 
 void SoundPlayer::Stop(float fade_out_duration) {
-  if (!input_->audio_bus)
+  if (!input_->IsValid())
     return;
 
   if (fade_out_duration > 0)
     input_->SetAmplitudeInc(
-        -1.0f / (input_->audio_bus->sample_rate() * fade_out_duration));
+        -1.0f / (input_->GetAudioBus()->sample_rate() * fade_out_duration));
   else
     input_->Stop();
 }
diff --git a/src/engine/sound_player.h b/src/engine/sound_player.h
index 9b692b2..7b0cb6b 100644
--- a/src/engine/sound_player.h
+++ b/src/engine/sound_player.h
@@ -9,7 +9,7 @@
 namespace eng {
 
 class AudioBus;
-struct MixerInput;
+class MixerInput;
 
 class SoundPlayer {
  public: