WIP audio play and pause

9 files changed, 559 insertions, 314 deletions

diff --git a/src/drivers/CMakeLists.txt b/src/drivers/CMakeLists.txt
index 3b3c4a65..899fcf79 100644
--- a/src/drivers/CMakeLists.txt
+++ b/src/drivers/CMakeLists.txt
@@ -1,6 +1,6 @@
 idf_component_register(
   SRCS "dac.cpp" "gpio-expander.cpp" "battery.cpp" "storage.cpp" "i2c.cpp"
-  "playback.cpp" "display.cpp" "display-init.cpp" "spi.cpp" 
+  "audio_playback.cpp" "i2s_audio_output.cpp" "display.cpp" "display-init.cpp" "spi.cpp" 
   INCLUDE_DIRS "include"
   REQUIRES "esp_adc_cal" "fatfs" "audio_pipeline" "audio_stream" "result" "lvgl")
 target_compile_options(${COMPONENT_LIB} PRIVATE ${EXTRA_WARNINGS})
diff --git a/src/drivers/audio_playback.cpp b/src/drivers/audio_playback.cpp
new file mode 100644
index 00000000..b38d0bd3
--- /dev/null
+++ b/src/drivers/audio_playback.cpp
@@ -0,0 +1,295 @@
+#include "audio_playback.hpp"
+
+#include "audio_output.hpp"
+#include "dac.hpp"
+
+#include <algorithm>
+#include <cstdint>
+#include <exception>
+#include <memory>
+#include <string_view>
+
+#include "audio_element.h"
+#include "audio_event_iface.h"
+#include "audio_pipeline.h"
+#include "driver/i2s.h"
+#include "esp_err.h"
+#include "freertos/portmacro.h"
+#include "mp3_decoder.h"
+
+static const char* kTag = "PLAYBACK";
+static const char* kSource = "src";
+static const char* kEncoder = "enc";
+static const char* kSink = "sink";
+
+static bool endsWith(std::string_view str, std::string_view suffix) {
+    return str.size() >= suffix.size() && 0 == str.compare(str.size()-suffix.size(), suffix.size(), suffix);
+}
+
+static void toLower(std::string &str) {
+  std::transform(str.begin(), str.end(), str.begin(),
+                 [](unsigned char c) { return std::tolower(c); });
+}
+
+namespace drivers {
+
+static audio_element_status_t status_from_the_void(void* status) {
+  uintptr_t as_pointer_int = reinterpret_cast<uintptr_t>(status);
+  return static_cast<audio_element_status_t>(as_pointer_int);
+}
+
+auto AudioPlayback::create(std::unique_ptr<IAudioOutput> output)
+    -> cpp::result<std::unique_ptr<AudioPlayback>, Error> {
+  audio_pipeline_handle_t pipeline;
+  audio_element_handle_t fatfs_stream_reader;
+  audio_event_iface_handle_t event_interface;
+
+  audio_pipeline_cfg_t pipeline_config =
+      audio_pipeline_cfg_t(DEFAULT_AUDIO_PIPELINE_CONFIG());
+  pipeline = audio_pipeline_init(&pipeline_config);
+  if (pipeline == NULL) {
+    return cpp::fail(Error::PIPELINE_INIT);
+  }
+
+  fatfs_stream_cfg_t fatfs_stream_config =
+      fatfs_stream_cfg_t(FATFS_STREAM_CFG_DEFAULT());
+  fatfs_stream_config.type = AUDIO_STREAM_READER;
+  fatfs_stream_reader = fatfs_stream_init(&fatfs_stream_config);
+  if (fatfs_stream_reader == NULL) {
+    return cpp::fail(Error::FATFS_INIT);
+  }
+
+  audio_event_iface_cfg_t event_config = AUDIO_EVENT_IFACE_DEFAULT_CFG();
+  event_interface = audio_event_iface_init(&event_config);
+
+  audio_pipeline_set_listener(pipeline, event_interface);
+  audio_element_msg_set_listener(fatfs_stream_reader, event_interface);
+  audio_element_msg_set_listener(output->GetAudioElement(), event_interface);
+
+  audio_pipeline_register(pipeline, fatfs_stream_reader, kSource);
+  audio_pipeline_register(pipeline, outut->GetAudioElement(), kSink);
+
+
+  return std::make_unique<AudioPlayback>(output, pipeline, fatfs_stream_reader, event_interface
+}
+
+AudioPlayback::AudioPlayback(std::unique_ptr<IAudioOutput> output,
+                                   audio_pipeline_handle_t pipeline,
+                                   audio_element_handle_t source_element,
+                                   audio_event_iface_handle_t event_interface,
+                                   audio_element_handle_t mp3_decoder)
+    : output_(std::move(outout)),
+      pipeline_(pipeline),
+      source_element_(source_element),
+      event_interface_(event_interface) {}
+
+AudioPlayback::~AudioPlayback() {
+  audio_pipeline_remove_listener(pipeline_);
+  audio_element_msg_remove_listener(source_element_, event_interface_);
+  audio_element_msg_remove_listener(output_->GetAudioElement(), event_interface_);
+
+  audio_pipeline_stop(pipeline_);
+  audio_pipeline_wait_for_stop(pipeline_);
+  audio_pipeline_terminate(pipeline_);
+
+  ReconfigurePipeline(NONE);
+
+  audio_pipeline_unregister(pipeline_, source_element_);
+  audio_pipeline_unregister(pipeline_, output_->GetAudioElement());
+
+  audio_event_iface_destroy(event_interface_);
+
+  audio_pipeline_deinit(pipeline_);
+  audio_element_deinit(source_element_);
+}
+
+void AudioPlayback::Play(const std::string& filename) {
+  if (GetPlaybackState() != STOPPED) {
+    audio_pipeline_stop(pipeline_);
+    audio_pipeline_wait_for_stop(pipeline_);
+    audio_pipeline_terminate(pipeline_);
+  }
+
+  current_state_ = PLAYING;
+  Decoder decoder = GetDecoderForFilename(filename);
+  ReconfigurePipeline(decoder);
+  audio_element_set_uri(source_element_, filename.c_str());
+  audio_pipeline_reset_ringbuffer(pipeline_);
+  audio_pipeline_reset_elements(pipeline_);
+  audio_pipeline_run(pipeline_);
+  dac_->WriteVolume(volume_);
+}
+
+void AudioPlayback::Resume() {
+  if (GetPlaybackState() == PAUSED) {
+    current_state_ = PLAYING;
+    audio_pipeline_resume(pipeline_);
+  }
+}
+void AudioPlayback::Pause() {
+  if (GetPlaybackState() == PLAYING) {
+    current_state_ = PAUSED;
+    audio_pipeline_pause(pipeline_);
+  }
+}
+
+auto AudioPlayback::GetPlaybackState() -> PlaybackState {
+  return current_state_;
+}
+
+void AudioPlayback::ProcessEvents(uint16_t max_time_ms) {
+  if (current_state_ == STOPPED) {
+    return;
+  }
+  while (1) {
+    audio_event_iface_msg_t event;
+    esp_err_t err =
+        audio_event_iface_listen(event_interface_, &event, pdMS_TO_TICKS(max_time_ms));
+    if (err != ESP_OK) {
+      ESP_LOGE(kTag, "error listening for event:%x", err);
+      continue;
+    }
+
+    if (event.source_type == AUDIO_ELEMENT_TYPE_ELEMENT &&
+        event.source == (void*)decoder_ &&
+        event.cmd == AEL_MSG_CMD_REPORT_MUSIC_INFO) {
+      audio_element_info_t music_info;
+      audio_element_getinfo(decoder_, &music_info);
+      ESP_LOGI(kTag, "sample_rate=%d, bits=%d, ch=%d", music_info.sample_rates,
+               music_info.bits, music_info.channels);
+    }
+
+    if (event.source_type == AUDIO_ELEMENT_TYPE_ELEMENT &&
+        event.source == (void*)source_element_ &&
+        event.cmd == AEL_MSG_CMD_REPORT_STATUS) {
+      audio_element_status_t status = status_from_the_void(event.data);
+      if (status == AEL_STATUS_STATE_FINISHED) {
+        // TODO: Could we change the uri here? hmm.
+      }
+    }
+
+    if (event.source_type == AUDIO_ELEMENT_TYPE_ELEMENT &&
+        event.source == (void*)output_->GetAudioElement() &&
+        event.cmd == AEL_MSG_CMD_REPORT_STATUS) {
+      audio_element_status_t status = status_from_the_void(event.data);
+      if (status == AEL_STATUS_STATE_FINISHED) {
+        if (next_filename_ != "") {
+          Decoder decoder = GetDecoderForFilename(next_filename_);
+          if (decoder == decoder_type_) {
+            audio_element_set_uri(source_element_, next_filename_);
+            audio_pipeline_reset_ringbuffer(pipeline_);
+            audio_pipeline_reset_elements(pipeline_);
+            audio_pipeline_change_state(pipeline_, AEL_STATE_INIT);
+            audio_pipeline_run(pipeline_);
+          } else {
+            Play(next_filename_);
+          }
+          next_filename_ = "";
+        } else {
+          audio_pipeline_stop(pipeline_);
+          audio_pipeline_wait_for_stop(pipeline_);
+          audio_pipeline_terminate(pipeline_);
+          current_state_ = STOPPED;
+        }
+        return;
+      }
+    }
+
+    if (event.need_free_data) {
+      ESP_LOGI(kTag, "freeing event data");
+      free(event.data);
+    }
+  }
+}
+
+void AudioPlayback::set_next_file(const std::string& filename) {
+  next_filename_ = filename;
+}
+
+void AudioPlayback::set_volume(uint8_t volume) {
+  volume_ = volume;
+  // TODO: don't write immediately if we're muted to change track or similar.
+  output_->SetVolume(volume);
+}
+
+auto AudioPlayback::volume() -> uint8_t {
+  return volume_;
+}
+
+auto AudioPlayback::GetDecoderForFilename(std::string filename) -> Decoder {
+  toLower(filename);
+  if (endsWith(filename, "mp3")) {
+    return MP3;
+  }
+  if (endsWith(filename, "amr") || endsWith(filename, "wamr") {
+    return AMR;
+  }
+  if (endsWith(filename, "opus")) {
+    return OPUS;
+  }
+  if (endsWith(filename, "ogg")) {
+    return OGG;
+  }
+  if (endsWith(filename, "flac")) {
+    return FLAC;
+  }
+  if (endsWith(filename, "wav")) {
+    return WAV;
+  }
+  if (endsWith(filename, "aac") || endsWith(filename, "m4a") || endsWith(filename, "ts") || endsWith(filename, "mp4")) {
+    return AAC;
+  }
+  return NONE;
+}
+
+auto AudioPlayback::CreateDecoder(Decoder decoder) -> audio_element_handle_t {
+  switch (decoder) {
+    case MP3:
+      mp3_decoder_cfg_t config = DEFAULT_MP3_DECODER_CONFIG();
+      return mp3_decoder_init(&config);
+    case AMR:
+      amr_decoder_cfg_t  config  = DEFAULT_AMR_DECODER_CONFIG();
+      return amr_decoder_init(&config);
+    case OPUS:
+      opus_decoder_cfg_t config = DEFAULT_OPUS_DECODER_CONFIG();
+      return decoder_opus_init(&config);
+    case OGG:
+      ogg_decoder_cfg_t  config  = DEFAULT_OGG_DECODER_CONFIG();
+      return ogg_decoder_init(&config);
+    case FLAC:
+      flac_decoder_cfg_t config = DEFAULT_FLAC_DECODER_CONFIG();
+      return flac_decoder_init(&config);
+    case WAV:
+      wav_decoder_cfg_t  config  = DEFAULT_WAV_DECODER_CONFIG();
+      return wav_decoder_init(&config);
+    case AAC:
+      aac_decoder_cfg_t  aac_dec_cfg  = DEFAULT_AAC_DECODER_CONFIG();
+      return aac_decoder_init(&aac_dec_cfg);
+    default:
+      return nullptr;
+  }
+}
+
+void AudioPlayback::ReconfigurePipeline(Decoder decoder) {
+  if (decoder_type_ == decoder) {
+    return;
+  }
+
+  if (decoder_type_ != NONE) {
+    audio_pipeline_unlink(pipeline);
+    audio_element_msg_remove_listener(decoder_, event_interface_);
+    audio_pipeline_unregister(pipeline_, decoder_);
+    audio_element_deinit(decoder_);
+  }
+
+  if (decoder != NONE) {
+    decoder_ = CreateDecoder(decoder);
+    decoder_type_ = decoder;
+    audio_pipeline_register(pipeline_, decoder_, kDecoder);
+    audio_element_msg_set_listener(decoder_, event_interface_);
+    static const char* link_tag[3] = {kSource, kDecoder, kSink};
+    audio_pipeline_link(pipeline, &link_tag[0], 3);
+  }
+}
+
+}  // namespace drivers
diff --git a/src/drivers/i2s_audio_output.cpp b/src/drivers/i2s_audio_output.cpp
new file mode 100644
index 00000000..6b231f0e
--- /dev/null
+++ b/src/drivers/i2s_audio_output.cpp
@@ -0,0 +1,92 @@
+#include "i2s_audio_output.hpp"
+#include <algorithm>
+#include "audio_output.hpp"
+#include "gpio-expander.hpp"
+
+static const i2s_port_t kI2SPort = I2S_NUM_0;
+
+namespace drivers {
+
+auto I2SAudioOutput::create(GpioExpander *expander)
+    -> cpp::result<std::unique_ptr<I2SAudioOutput>, Error> {
+
+  // First, we need to perform initial configuration of the DAC chip.
+  auto dac_result = drivers::AudioDac::create(expander);
+  if (dac_result.has_error()) {
+    ESP_LOGE(TAG, "failed to init dac: %d", dac_result.error());
+    return cpp::fail(DAC_CONFIG);
+  }
+  std::unique_ptr<AudioDac> dac = std::move(dac_result.value());
+
+  // Soft mute immediately, in order to minimise any clicks and pops caused by
+  // the initial output element and pipeline configuration.
+  dac->WriteVolume(255);
+
+  i2s_stream_cfg_t i2s_stream_config = i2s_stream_cfg_t{
+      .type = AUDIO_STREAM_WRITER,
+      .i2s_config =
+          {
+              // static_cast bc esp-adf uses enums incorrectly
+              .mode = static_cast<i2s_mode_t>(I2S_MODE_MASTER | I2S_MODE_TX),
+              .sample_rate = 44100,
+              .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,
+              .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
+              .communication_format = I2S_COMM_FORMAT_STAND_I2S,
+              .intr_alloc_flags = ESP_INTR_FLAG_LOWMED,
+              .dma_buf_count = 8,
+              .dma_buf_len = 64,
+              .use_apll = false,
+              .tx_desc_auto_clear = false,
+              .fixed_mclk = 0,
+              .mclk_multiple = I2S_MCLK_MULTIPLE_DEFAULT,
+              .bits_per_chan = I2S_BITS_PER_CHAN_DEFAULT,
+          },
+      .i2s_port = kI2SPort,
+      .use_alc = false,
+      .volume = 0,  // Does nothing; use AudioDac to change this.
+      .out_rb_size = I2S_STREAM_RINGBUFFER_SIZE,
+      .task_stack = I2S_STREAM_TASK_STACK,
+      .task_core = I2S_STREAM_TASK_CORE,
+      .task_prio = I2S_STREAM_TASK_PRIO,
+      .stack_in_ext = false,
+      .multi_out_num = 0,
+      .uninstall_drv = true,
+      .need_expand = false,
+      .expand_src_bits = I2S_BITS_PER_SAMPLE_16BIT,
+  };
+  i2s_stream_writer = i2s_stream_init(&i2s_stream_config);
+  if (i2s_stream_writer == NULL) {
+    return cpp::fail(Error::STREAM_INIT);
+  }
+
+  // NOTE: i2s_stream_init does some additional setup that hardcodes MCK as
+  // GPIO0. This happens to work fine for us, but be careful if changing.
+  i2s_pin_config_t pin_config = {.mck_io_num = GPIO_NUM_0,
+                                 .bck_io_num = GPIO_NUM_26,
+                                 .ws_io_num = GPIO_NUM_27,
+                                 .data_out_num = GPIO_NUM_5,
+                                 .data_in_num = I2S_PIN_NO_CHANGE};
+  if (esp_err_t err = i2s_set_pin(kI2SPort, &pin_config) != ESP_OK) {
+    ESP_LOGE(kTag, "failed to configure i2s pins %x", err);
+    return cpp::fail(Error::I2S_CONFIG);
+  }
+
+  return std::make_unique<I2SAudioOutput>(dac, i2s_stream_writer);
+}
+
+I2SAudioOutput(std::unique<AudioDac> dac, audio_element_handle_t element) : IAudioOutput(element), dac_(dac) {}
+~I2SAudioOutput() {
+  // TODO: power down the DAC.
+}
+
+auto I2SAudioOutput::SetVolume(uint8_t volume) -> void {
+  dac_->WriteVolume(255);
+}
+
+auto I2SAudioOutput::Configure(audio_element_info_t info) -> void {
+      audio_element_setinfo(element_, &music_info);
+      i2s_stream_set_clk(element_, music_info.sample_rates,
+                         music_info.bits, music_info.channels);
+}
+
+}
diff --git a/src/drivers/include/a2dp_audio_output.hpp b/src/drivers/include/a2dp_audio_output.hpp
new file mode 100644
index 00000000..43b55956
--- /dev/null
+++ b/src/drivers/include/a2dp_audio_output.hpp
@@ -0,0 +1,15 @@
+#pragma once
+
+#include "audio_common.h"
+#include "audio_element.h"
+#include "audio_output.hpp"
+#include <cstdint>
+
+namespace drivers {
+
+class A2DPAudioOutput : IAudioOutput {
+  public:
+    virtual auto SetVolume(uint8_t volume) -> void;
+};
+
+} // namespace drivers
diff --git a/src/drivers/include/audio_output.hpp b/src/drivers/include/audio_output.hpp
new file mode 100644
index 00000000..63cba465
--- /dev/null
+++ b/src/drivers/include/audio_output.hpp
@@ -0,0 +1,27 @@
+#pragma once
+
+#include "audio_common.h"
+#include "audio_element.h"
+#include <cstdint>
+
+namespace drivers {
+
+class IAudioOutput {
+  public:
+    IAudioOutput(audio_element_handle_t element) : element_(element) {}
+    virtual ~IAudioOutput() {
+      audio_element_deinit(element_);
+    }
+
+    auto GetAudioElement() -> audio_element_handle_t {
+      return element_;
+    }
+
+    virtual auto SetVolume(uint8_t volume) -> void = 0;
+    virtual auto Configure(audio_element_info_t info) -> void = 0;
+
+  protected:
+    audio_element_handle_t element_;
+};
+
+} // namespace drivers
diff --git a/src/drivers/include/audio_playback.hpp b/src/drivers/include/audio_playback.hpp
new file mode 100644
index 00000000..dd0f7f7a
--- /dev/null
+++ b/src/drivers/include/audio_playback.hpp
@@ -0,0 +1,99 @@
+#pragma once
+
+#include "audio_output.hpp"
+#include "dac.hpp"
+#include "storage.hpp"
+
+#include <cstdint>
+#include <memory>
+#include <string>
+
+#include "audio_common.h"
+#include "audio_element.h"
+#include "audio_event_iface.h"
+#include "audio_pipeline.h"
+#include "esp_err.h"
+#include "fatfs_stream.h"
+#include "i2s_stream.h"
+#include "mp3_decoder.h"
+#include "result.hpp"
+
+namespace drivers {
+
+/*
+ * Sends an I2S audio stream to the DAC. Includes basic controls for pausing
+ * and resuming the stream, as well as support for gapless playback of the next
+ * queued song, but does not implement any kind of sophisticated queing or
+ * playback control; these should be handled at a higher level.
+ */
+class AudioPlayback {
+ public:
+  enum Error { FATFS_INIT, I2S_INIT, PIPELINE_INIT };
+  static auto create(std::unique_ptr<IAudioOutput> output)
+      -> cpp::result<std::unique_ptr<AudioPlayback>, Error>;
+
+  AudioPlayback(std::unqiue_ptr<IAudioOutput> output,
+                   audio_pipeline_handle_t pipeline,
+                   audio_element_handle_t source_element,
+                   audio_event_iface_handle_t event_interface);
+  ~AudioPlayback();
+
+  /*
+   * Replaces any currently playing file with the one given, and begins
+   * playback.
+   *
+   * Any value set in `set_next_file` is cleared by this method.
+   */
+  void Play(const std::string& filename);
+  /* Toogle between resumed and paused. */
+  void Toggle();
+  void Resume();
+  void Pause();
+
+  enum PlaybackState { PLAYING, PAUSED, STOPPED };
+  auto GetPlaybackState() -> PlaybackState;
+
+  /*
+   * Handles any pending events from the underlying audio pipeline. This must
+   * be called regularly in order to handle configuring the I2S stream for
+   * different audio types (e.g. sample rate, bit depth), and for gapless
+   * playback.
+   */
+  void ProcessEvents(uint16_t max_time_ms);
+
+  /*
+   * Sets the file that should be played immediately after the current file
+   * finishes. This is used for gapless playback
+   */
+  void set_next_file(const std::string& filename);
+
+  void set_volume(uint8_t volume);
+  auto volume() -> uint8_t;
+
+  // Not copyable or movable.
+  AudioPlayback(const AudioPlayback&) = delete;
+  AudioPlayback& operator=(const AudioPlayback&) = delete;
+
+ private:
+  PlaybackState current_state_;
+
+  enum Decoder {NONE, MP3, AMR, OPUS, OGG, FLAC, WAV, AAC};
+  auto GetDecoderForFilename(std::string filename) -> Decoder;
+  auto CreateDecoder(Decoder decoder) -> audio_element_handle_t;
+  void ReconfigurePipeline();
+
+  std::unique_ptr<IAudioOutput> output_;
+  std::mutex playback_lock_;
+
+  std::string next_filename_ = "";
+  uint8_t volume_;
+
+  audio_pipeline_handle_t pipeline_;
+  audio_element_handle_t source_element_;
+  audio_event_iface_handle_t event_interface_;
+
+  audio_element_handle_t decoder_ = nullptr;
+  Decoder decoder_type_ = NONE;
+};
+
+}  // namespace drivers
diff --git a/src/drivers/include/i2s_audio_output.hpp b/src/drivers/include/i2s_audio_output.hpp
new file mode 100644
index 00000000..531bddbc
--- /dev/null
+++ b/src/drivers/include/i2s_audio_output.hpp
@@ -0,0 +1,30 @@
+#pragma once
+
+#include "audio_common.h"
+#include "audio_element.h"
+#include "audio_output.hpp"
+#include "gpio-expander.hpp"
+#include <cstdint>
+#include <memory>
+#include "result.hpp"
+#include "dac.hpp"
+
+namespace drivers {
+
+class I2SAudioOutput : public IAudioOutput {
+  public:
+  enum Error { DAC_CONFIG, I2S_CONFIG, STREAM_INIT };
+    static auto create(GpioExpander* expander)
+        -> cpp::result<std::unique_ptr<I2SAudioOutput>, Error>;
+
+  I2SAudioOutput(AudioDac* dac, audio_element_handle_t element);
+  ~I2SAudioOutput();
+
+  virtual auto SetVolume(uint8_t volume) -> void;
+  virtual auto Configure(audio_element_info_t info) -> void;
+
+  private:
+    std::unique_ptr<AudioDac> dac_;
+};
+
+} // namespace drivers
diff --git a/src/drivers/include/playback.hpp b/src/drivers/include/playback.hpp
deleted file mode 100644
index 5fa7ab38..00000000
--- a/src/drivers/include/playback.hpp
+++ /dev/null
@@ -1,67 +0,0 @@
-#pragma once
-
-#include "dac.hpp"
-#include "storage.hpp"
-
-#include <cstdint>
-#include <memory>
-#include <string>
-
-#include "audio_common.h"
-#include "audio_element.h"
-#include "audio_event_iface.h"
-#include "audio_pipeline.h"
-#include "esp_err.h"
-#include "fatfs_stream.h"
-#include "i2s_stream.h"
-#include "mp3_decoder.h"
-#include "result.hpp"
-
-namespace drivers {
-
-class DacAudioPlayback {
- public:
-  enum Error { PIPELINE_INIT };
-  static auto create(AudioDac* dac)
-      -> cpp::result<std::unique_ptr<DacAudioPlayback>, Error>;
-
-  DacAudioPlayback(AudioDac* dac,
-                   audio_pipeline_handle_t pipeline,
-                   audio_element_handle_t fatfs_stream_reader,
-                   audio_element_handle_t i2s_stream_writer,
-                   audio_event_iface_handle_t event_interface,
-                   audio_element_handle_t mp3_decoder);
-  ~DacAudioPlayback();
-
-  void Play(const std::string& filename);
-  void Resume();
-  void Pause();
-
-  void ProcessEvents();
-
-  /* for gapless */
-  void set_next_file(const std::string& filename);
-
-  void set_volume(uint8_t volume);
-  auto volume() -> uint8_t;
-
-  // Not copyable or movable.
-  DacAudioPlayback(const DacAudioPlayback&) = delete;
-  DacAudioPlayback& operator=(const DacAudioPlayback&) = delete;
-
- private:
-  AudioDac* dac_;
-  std::mutex playback_lock_;
-
-  std::string next_filename_;
-  uint8_t volume_;
-
-  audio_pipeline_handle_t pipeline_;
-  audio_element_handle_t fatfs_stream_reader_;
-  audio_element_handle_t i2s_stream_writer_;
-  audio_event_iface_handle_t event_interface_;
-
-  audio_element_handle_t mp3_decoder_;
-};
-
-}  // namespace drivers
diff --git a/src/drivers/playback.cpp b/src/drivers/playback.cpp
deleted file mode 100644
index a9290613..00000000
--- a/src/drivers/playback.cpp
+++ /dev/null
@@ -1,246 +0,0 @@
-#include "playback.hpp"
-
-#include "dac.hpp"
-
-#include <cstdint>
-
-#include "audio_element.h"
-#include "audio_event_iface.h"
-#include "audio_pipeline.h"
-#include "driver/i2s.h"
-#include "esp_err.h"
-#include "freertos/portmacro.h"
-#include "mp3_decoder.h"
-
-static const char* kTag = "PLAYBACK";
-static const i2s_port_t kI2SPort = I2S_NUM_0;
-
-namespace drivers {
-
-static audio_element_status_t status_from_the_void(void* status) {
-  uintptr_t as_pointer_int = reinterpret_cast<uintptr_t>(status);
-  return static_cast<audio_element_status_t>(as_pointer_int);
-}
-
-auto DacAudioPlayback::create(AudioDac* dac)
-    -> cpp::result<std::unique_ptr<DacAudioPlayback>, Error> {
-  // Ensure we're soft-muted before initialising, in order to reduce protential
-  // clicks and pops.
-  dac->WriteVolume(255);
-
-  audio_pipeline_handle_t pipeline;
-  audio_element_handle_t fatfs_stream_reader;
-  audio_element_handle_t i2s_stream_writer;
-  audio_event_iface_handle_t event_interface;
-
-  audio_pipeline_cfg_t pipeline_config =
-      audio_pipeline_cfg_t(DEFAULT_AUDIO_PIPELINE_CONFIG());
-  pipeline = audio_pipeline_init(&pipeline_config);
-  if (pipeline == NULL) {
-    return cpp::fail(Error::PIPELINE_INIT);
-  }
-
-  fatfs_stream_cfg_t fatfs_stream_config =
-      fatfs_stream_cfg_t(FATFS_STREAM_CFG_DEFAULT());
-  fatfs_stream_config.type = AUDIO_STREAM_READER;
-  fatfs_stream_reader = fatfs_stream_init(&fatfs_stream_config);
-  if (fatfs_stream_reader == NULL) {
-    return cpp::fail(Error::PIPELINE_INIT);
-  }
-
-  i2s_stream_cfg_t i2s_stream_config = i2s_stream_cfg_t{
-      .type = AUDIO_STREAM_WRITER,
-      .i2s_config =
-          {
-              // static_cast bc esp-adf uses enums incorrectly
-              .mode = static_cast<i2s_mode_t>(I2S_MODE_MASTER | I2S_MODE_TX),
-              .sample_rate = 44100,
-              .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,
-              .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
-              .communication_format = I2S_COMM_FORMAT_STAND_I2S,
-              .intr_alloc_flags = ESP_INTR_FLAG_LOWMED,
-              .dma_buf_count = 8,
-              .dma_buf_len = 64,
-              .use_apll = false,
-              .tx_desc_auto_clear = false,
-              .fixed_mclk = 0,
-              .mclk_multiple = I2S_MCLK_MULTIPLE_DEFAULT,
-              .bits_per_chan = I2S_BITS_PER_CHAN_DEFAULT,
-          },
-      .i2s_port = kI2SPort,
-      .use_alc = false,
-      .volume = 0,  // Does nothing; use AudioDac to change this.
-      .out_rb_size = I2S_STREAM_RINGBUFFER_SIZE,
-      .task_stack = I2S_STREAM_TASK_STACK,
-      .task_core = I2S_STREAM_TASK_CORE,
-      .task_prio = I2S_STREAM_TASK_PRIO,
-      .stack_in_ext = false,
-      .multi_out_num = 0,
-      .uninstall_drv = true,
-      .need_expand = false,
-      .expand_src_bits = I2S_BITS_PER_SAMPLE_16BIT,
-  };
-  i2s_stream_writer = i2s_stream_init(&i2s_stream_config);
-  if (i2s_stream_writer == NULL) {
-    return cpp::fail(Error::PIPELINE_INIT);
-  }
-
-  // NOTE: i2s_stream_init does some additional setup that hardcodes MCK as
-  // GPIO0. This happens to work fine for us, but be careful if changing.
-  i2s_pin_config_t pin_config = {.mck_io_num = GPIO_NUM_0,
-                                 .bck_io_num = GPIO_NUM_26,
-                                 .ws_io_num = GPIO_NUM_27,
-                                 .data_out_num = GPIO_NUM_5,
-                                 .data_in_num = I2S_PIN_NO_CHANGE};
-  if (esp_err_t err = i2s_set_pin(kI2SPort, &pin_config) != ESP_OK) {
-    ESP_LOGE(kTag, "failed to configure i2s pins %x", err);
-    return cpp::fail(Error::PIPELINE_INIT);
-  }
-
-  // TODO: Create encoders dynamically when we need them.
-  audio_element_handle_t mp3_decoder;
-  mp3_decoder_cfg_t mp3_config =
-      mp3_decoder_cfg_t(DEFAULT_MP3_DECODER_CONFIG());
-  mp3_decoder = mp3_decoder_init(&mp3_config);
-  assert(mp3_decoder != NULL);
-
-  audio_event_iface_cfg_t event_config = AUDIO_EVENT_IFACE_DEFAULT_CFG();
-  event_interface = audio_event_iface_init(&event_config);
-
-  audio_pipeline_set_listener(pipeline, event_interface);
-  audio_element_msg_set_listener(fatfs_stream_reader, event_interface);
-  audio_element_msg_set_listener(mp3_decoder, event_interface);
-  audio_element_msg_set_listener(i2s_stream_writer, event_interface);
-
-  // TODO: most of this is likely post-init, since it involves a decoder.
-  // All the elements of our pipeline have been initialised. Now switch them
-  // together.
-  audio_pipeline_register(pipeline, fatfs_stream_reader, "file");
-  audio_pipeline_register(pipeline, mp3_decoder, "dec");
-  audio_pipeline_register(pipeline, i2s_stream_writer, "i2s");
-
-  const char* link_tag[3] = {"file", "dec", "i2s"};
-  audio_pipeline_link(pipeline, &link_tag[0], 3);
-
-  return std::make_unique<DacAudioPlayback>(dac, pipeline, fatfs_stream_reader,
-                                            i2s_stream_writer, event_interface,
-                                            mp3_decoder);
-}
-
-DacAudioPlayback::DacAudioPlayback(AudioDac* dac,
-                                   audio_pipeline_handle_t pipeline,
-                                   audio_element_handle_t fatfs_stream_reader,
-                                   audio_element_handle_t i2s_stream_writer,
-                                   audio_event_iface_handle_t event_interface,
-                                   audio_element_handle_t mp3_decoder)
-    : dac_(dac),
-      pipeline_(pipeline),
-      fatfs_stream_reader_(fatfs_stream_reader),
-      i2s_stream_writer_(i2s_stream_writer),
-      event_interface_(event_interface),
-      mp3_decoder_(mp3_decoder) {}
-
-DacAudioPlayback::~DacAudioPlayback() {
-  dac_->WriteVolume(255);
-
-  audio_pipeline_remove_listener(pipeline_);
-  audio_element_msg_remove_listener(fatfs_stream_reader_, event_interface_);
-  audio_element_msg_remove_listener(mp3_decoder_, event_interface_);
-  audio_element_msg_remove_listener(i2s_stream_writer_, event_interface_);
-
-  audio_pipeline_stop(pipeline_);
-  audio_pipeline_wait_for_stop(pipeline_);
-  audio_pipeline_terminate(pipeline_);
-
-  audio_pipeline_unregister(pipeline_, fatfs_stream_reader_);
-  audio_pipeline_unregister(pipeline_, mp3_decoder_);
-  audio_pipeline_unregister(pipeline_, i2s_stream_writer_);
-
-  audio_event_iface_destroy(event_interface_);
-
-  audio_pipeline_deinit(pipeline_);
-  audio_element_deinit(fatfs_stream_reader_);
-  audio_element_deinit(i2s_stream_writer_);
-  audio_element_deinit(mp3_decoder_);
-}
-
-void DacAudioPlayback::Play(const std::string& filename) {
-  dac_->WriteVolume(255);
-  // TODO: handle reconfiguring the pipeline if needed.
-  audio_element_set_uri(fatfs_stream_reader_, filename.c_str());
-  audio_pipeline_run(pipeline_);
-  dac_->WriteVolume(volume_);
-}
-
-void DacAudioPlayback::Resume() {
-  // TODO.
-}
-void DacAudioPlayback::Pause() {
-  // TODO.
-}
-
-void DacAudioPlayback::ProcessEvents() {
-  while (1) {
-    audio_event_iface_msg_t event;
-    esp_err_t err =
-        audio_event_iface_listen(event_interface_, &event, portMAX_DELAY);
-    if (err != ESP_OK) {
-      ESP_LOGI(kTag, "error listening for event:%x", err);
-      continue;
-    }
-    ESP_LOGI(kTag, "received event, cmd %i", event.cmd);
-
-    if (event.source_type == AUDIO_ELEMENT_TYPE_ELEMENT &&
-        event.source == (void*)mp3_decoder_ &&
-        event.cmd == AEL_MSG_CMD_REPORT_MUSIC_INFO) {
-      audio_element_info_t music_info;
-      audio_element_getinfo(mp3_decoder_, &music_info);
-      ESP_LOGI(kTag, "sample_rate=%d, bits=%d, ch=%d", music_info.sample_rates,
-               music_info.bits, music_info.channels);
-      audio_element_setinfo(i2s_stream_writer_, &music_info);
-      i2s_stream_set_clk(i2s_stream_writer_, music_info.sample_rates,
-                         music_info.bits, music_info.channels);
-    }
-
-    if (event.source_type == AUDIO_ELEMENT_TYPE_ELEMENT &&
-        event.source == (void*)fatfs_stream_reader_ &&
-        event.cmd == AEL_MSG_CMD_REPORT_STATUS) {
-      audio_element_status_t status = status_from_the_void(event.data);
-      if (status == AEL_STATUS_STATE_FINISHED) {
-        // TODO: enqueue next track?
-      }
-    }
-
-    if (event.source_type == AUDIO_ELEMENT_TYPE_ELEMENT &&
-        event.source == (void*)i2s_stream_writer_ &&
-        event.cmd == AEL_MSG_CMD_REPORT_STATUS) {
-      audio_element_status_t status = status_from_the_void(event.data);
-      if (status == AEL_STATUS_STATE_FINISHED) {
-        // TODO.
-        return;
-      }
-    }
-
-    if (event.need_free_data) {
-      ESP_LOGI(kTag, "freeing event data");
-      free(event.data);
-    }
-  }
-}
-
-/* for gapless */
-void DacAudioPlayback::set_next_file(const std::string& filename) {
-  next_filename_ = filename;
-}
-
-void DacAudioPlayback::set_volume(uint8_t volume) {
-  volume_ = volume;
-  // TODO: don't write immediately if we're muting to change track or similar.
-  dac_->WriteVolume(volume);
-}
-
-auto DacAudioPlayback::volume() -> uint8_t {
-  return volume_;
-}
-
-}  // namespace drivers