WIP on our own pipeline

src/audio/README.md

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+
+FatfsAudioReader
+ - input if a queue of filenames.
+ - output is a cbor stream
+    - 1 header, like "this is a new file! this is the file type!
+    - followed by length-prefixed chunks of bytes
+ - runs in a task, which prompts it to read/write one chunk, then returns.
+ - task watches for kill signal, owns storage, etc.
+
+AudioDecoder
+ - input is the chunked bytes above.
+ - output is also a cbor stream
+    - 1 header, which is like a reconfiguration packet thing.
+    - "data that follows is this depth, this sample rate"
+    - also indicates whether the configuration is 'sudden' for soft muting?
+    - then length-prefixed chunks of bytes
+
+AudioOutput
+  - input is the output of the decoder
+  - outputs via writing to i2s_write, which copies data to a dma buffer
+  - therefore, safe for us to consume any kind of reconfiguration here.
+    - only issue is that we will need to wait for the dma buffers to drain before
+      we can reconfigure the driver. (i2s_zero_dma_buffer)
+ - this is important for i2s speed; we should avoid extra copy steps for the raw
+ - pcm stream
+ - input therefore needs to be two channels: one configuration channel, one bytes
+   channel
+
+
+How do things like seeking, and progress work?
+ - Reader knows where we are in terms of file size and position
+ - Decoder knows sample rate, frames, etc. for knowing how that maps into
+ - the time progress
+ - Output knows where we are as well in a sense, but only in terms of the PCM
+  output. this doesn't correspond to anything very well.
+
+  So, to seek:
+   - come up with your position. this is likely "where we are plus 10", or a
+   specific timecode. the decoder has what we need for the byte position of this
+   - tell the reader "hey we need to be in this file at this byte position
+   - reader clears its own output buffer (since it's been doing readahead) and
+    starts again at the given location
+  For current position, the decoder will need to track where in the file it's up
+  to.
+
+HEADERS + DATA:
+ - cbor seems sensible for headers. allocate a little working buffer, encode the
+  data, then send it out on the ringbuffer.
+ - the data itself is harder, since tinycbor doesn't support writing chunked indefinite
+  length stuff. this is a problem bc we need to give cbor the buffer up front, but
+  we don't know exactly how long things will be, so it ends up being slightly awkward 
+  and inefficient.
+  - we could also just like... write the struct i guess? that might be okay.
+  - gives us a format like <TYPE ENUM> <LENGTH> <DATA>
+  - could be smart with the type, use like a 32 bit int, and encode the length
+  - in there?
+  - then from the reader's perspective, it's:
+    - read 4 bytes, work out what's next
+    - read the next X bytes

src/audio/audio_task.cpp

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+#include "audio_task.hpp"
+
+#include <stdlib.h>
+
+#include <cstdint>
+
+#include "esp_heap_caps.h"
+#include "freertos/portmacro.h"
+#include "freertos/queue.h"
+#include "freertos/stream_buffer.h"
+
+#include "audio_element.hpp"
+
+namespace audio {
+
+static const TickType_t kCommandWaitTicks = 1;
+
+void audio_task(void* args) {
+  AudioTaskArgs* real_args = reinterpret_cast<AudioTaskArgs*>(args);
+  std::shared_ptr<IAudioElement> element = real_args->element;
+  delete real_args;
+
+  QueueHandle_t commands = element->InputCommandQueue();
+  StreamBufferHandle_t stream = element->InputBuffer();
+
+  // TODO: think about overflow.
+  uint8_t current_sequence_number;
+  uint8_t* frame_buffer =
+      (uint8_t*)heap_caps_malloc(kFrameSize, MALLOC_CAP_SPIRAM);
+
+  while (1) {
+    IAudioElement::Command command;
+    if (!xQueueReceive(commands, &command, kCommandWaitTicks)) {
+      element->ProcessIdle();
+      continue;
+    };
+
+    if (command.type == IAudioElement::SEQUENCE_NUMBER) {
+      if (command.sequence_number > current_sequence_number) {
+        current_sequence_number = command.sequence_number;
+      }
+
+      continue;
+    }
+
+    if (command.type == IAudioElement::READ) {
+      assert(command.read_size <= kFrameSize);
+      assert(stream != NULL);
+      xStreamBufferReceive(stream, &frame_buffer, command.read_size, 0);
+
+      if (command.sequence_number == current_sequence_number) {
+        element->ProcessData(frame_buffer, command.read_size);
+      }
+
+      continue;
+    }
+
+    if (command.type == IAudioElement::ELEMENT) {
+      assert(command.data != NULL);
+      if (command.sequence_number == current_sequence_number) {
+        element->ProcessElementCommand(command.data);
+      } else {
+        element->SkipElementCommand(command.data);
+      }
+    }
+
+    if (command.type == IAudioElement::QUIT) {
+      break;
+    }
+  }
+
+  element = nullptr;
+  free(frame_buffer);
+
+  xTaskDelete(NULL);
+}
+
+}  // namespace audio

src/audio/fatfs_audio_input.cpp

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+#include "fatfs_audio_input.hpp"
+#include <memory>
+
+#include "esp-adf/components/input_key_service/include/input_key_service.h"
+#include "esp_heap_caps.h"
+
+#include "audio_element.hpp"
+
+namespace audio {
+
+static const size_t kQueueItems = 0;
+static constexpr size_t kQueueItemSize = sizeof(IAudioElement::Command);
+static constexpr size_t kQueueSize = kQueueItems * kQueueItemSize;
+
+static const size_t kOutputBufferSize = 1024;
+
+FatfsAudioInput::FatfsAudioInput(std::shared_ptr<drivers::SdStorage> storage)
+    : IAudioElement(), storage_(storage) {
+  input_queue_memory_ = heap_caps_malloc(kQueueSize, MALLOC_CAP_SPIRAM);
+  input_queue_ = xQueueCreateStatic(
+      kQueueItems, kQueueItemSize, input_queue_memory_, &input_queue_metadata_);
+
+  output_queue_memory_ = heap_caps_malloc(kQueueSize, MALLOC_CAP_SPIRAM);
+  output_queue_ =
+      xQueueCreateStatic(kQueueItems, kQueueItemSize, output_queue_memory_,
+                         &output_queue_metadata_);
+
+  output_buffer_memory_ =
+      heap_caps_malloc(kOutputBufferSize, MALLOC_CAP_SPIRAM);
+  output_buffer_ =
+      xStreamBufferCreateStatic(kOutputBufferSize - 1, 1, output_buffer_memory_,
+                                &output_buffer_metadata_);
+}
+
+FatfsAudioInput::~FatfsAudioInput() {
+  vStreamBufferDelete(output_buffer_);
+  free(output_buffer_memory_);
+  vQueueDelete(output_queue_);
+  free(output_queue_memory_);
+  vQueueDelete(input_queue_);
+  free(input_queue_memory_);
+}
+
+auto FatfsAudioInput::InputCommandQueue() -> QueueHandle_t {
+  return input_queue_;
+}
+
+auto FatfsAudioInput::OutputCommandQueue() -> QueueHandle_t {
+  return output_queue_;
+}
+
+auto FatfsAudioInput::InputBuffer() -> StreamBufferHandle_t {
+  return nullptr;
+}
+
+auto FatfsAudioInput::OutputBuffer() -> StreamBufferHandle_t {
+  return output_buffer_;
+}
+
+auto FatfsAudioInput::ProcessElementCommand(void* command) -> void {
+  InputCommand *real = std::reinterpret_pointer_cast<input_key_service_add_key*>(command);
+
+  // TODO.
+}
+
+auto FatfsAudioInput::SkipElementCommand(void* command) -> void {
+  InputCommand *real = std::reinterpret_pointer_cast<input_key_service_add_key*>(command);
+  delete real;
+}
+
+auto FatfsAudioInput::ProcessData(uint8_t* data, uint16_t length) -> void {
+  // Not implemented.
+}
+
+auto FatfsAudioInput::ProcessIdle() -> void {
+  // TODO.
+}
+
+}  // namespace audio

src/audio/include/audio_backend.hpp

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+#pragma once
+
+#include <cstdint>
+namespace drivers {
+
+class IAudioBackend {
+ public:
+  virtual ~IAudioBackend() {}
+
+  enum SampleRate {};
+  enum BitDepth {};
+
+  virtual auto Configure(SampleRate sample_rate, BitDepth bit_depth)
+      -> bool = 0;
+  virtual auto WritePcmData(uint8_t* data, size_t length) -> bool = 0;
+
+  virtual auto SetVolume(uint8_t percent) -> void = 0;
+};
+
+}  // namespace drivers

src/audio/include/audio_decoder.hpp

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+#pragma once
+
+#include <cstddef>
+#include "ff.h"
+
+namespace audio {
+
+enum SampleRate {};
+enum BitDepth {};
+
+struct PcmStreamHeader {
+  SampleRate sample_rate;
+  BitDepth bit_depth;
+  bool configure_now;
+};
+
+class AudioDecoder {
+ public:
+  AudioDecoder();
+  ~AudioDecoder();
+
+  auto SetSource(RingbufHandle_t& source) -> void;
+
+  enum Status {};
+  auto ProcessChunk() -> Status;
+
+  auto GetOutputStream() const -> RingbufHandle_t;
+
+ private:
+  RingbufHandle_t input_;
+  RingbufHandle_t output_;
+};
+
+}  // namespace audio

src/audio/include/audio_element.hpp

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+#pragma once
+
+#include <cstdint>
+
+namespace audio {
+
+extern const std::size_t kMaxFrameSize;
+
+class IAudioElement {
+ public:
+  virtual ~IAudioElement();
+
+  enum CommandType {
+    /*
+     * Sets the sequence number of the most recent byte stream. Any commands
+     * received that have a lower sequence number than this will be discarded.
+     */
+    SEQUENCE_NUMBER,
+    /*
+     * Instructs this element to read a specific number of bytes from its
+     * input buffer.
+     */
+    READ_FRAME,
+    /*
+     * Represents an element-specific command. This handling of this is
+     * delegated to element implementations.
+     */
+    ELEMENT,
+    /* Instructs this element to shut down. */
+    QUIT,
+  };
+
+  struct Command {
+    CommandType type;
+    uint8_t sequence_number;
+    union {
+      void* data;
+      std::size_t frame_size;
+    };
+  };
+
+  /*
+   * Returns a queue that should be used for all communication with this
+   * element.
+   */
+  virtual auto InputCommandQueue() -> QueueHandle_t = 0;
+
+  /*
+   * Returns a buffer that will be used to stream input bytes to this element.
+   * This may be NULL, if this element represents a source, e.g. a FATFS
+   * reader.
+   */
+  virtual auto InputBuffer() -> StreamBufferHandle_t = 0;
+
+  /*
+   * Called when an element-specific command has been received.
+   */
+  virtual auto ProcessElementCommand(void* command) -> void = 0;
+
+  virtual auto SkipElementCommand(void* command) -> void = 0;
+
+  /*
+   * Called with the result of a read bytes command.
+   */
+  virtual auto ProcessData(uint8_t* data, uint16_t length) -> void = 0;
+
+  /*
+   * Called periodically when there are no pending commands.
+   */
+  virtual auto ProcessIdle() -> void = 0;
+};
+
+}  // namespace audio

src/audio/include/audio_task.hpp

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+#pragma once
+
+#include <memory>
+
+#include "audio_element.hpp"
+
+namespace audio {
+
+struct AudioTaskArgs {
+  std::shared_ptr<IAudioElement>& element;
+};
+
+void audio_task(void* args);
+
+}  // namespace audio

src/audio/include/fatfs_audio_input.hpp

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+#pragma once
+
+#include <cstdint>
+#include <memory>
+
+#include "freertos/FreeRTOS.h"
+#include "freertos/queue.h"
+#include "freertos/stream_buffer.h"
+
+#include "audio_element.hpp"
+#include "storage.hpp"
+
+namespace audio {
+
+class FatfsAudioInput : public IAudioElement {
+ public:
+  struct InputCommand {
+    std::string filename;
+  };
+
+  struct OutputCommand {
+    // TODO: does this actually need any special output?
+  };
+
+  FatfsAudioInput(std::shared_ptr<drivers::SdStorage> storage);
+  ~FatfsAudioInput();
+
+  auto OutputCommandQueue() -> QueueHandle_t;
+  auto OutputBuffer() -> StreamBufferHandle_t;
+
+ private:
+  std::shared_ptr<drivers::SdStorage> storage_;
+
+  uint8_t current_sequence = 0;
+
+  uint8_t* input_queue_memory_;
+  StaticQueue_t input_queue_metadata_;
+  QueueHandle_t input_queue_;
+
+  uint8_t* output_queue_memory_;
+  StaticQueue_t output_queue_metadata_;
+  QueueHandle_t output_queue_;
+
+  uint8_t* output_buffer_memory_;
+  StaticStreamBuffer_t output_buffer_metadata_;
+  StreamBufferHandle_t output_buffer_;
+};
+
+}  // namespace audio

src/codecs/README.md

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+# Software Codecs
+
+This component contains a collection of software decoders for various 

src/codecs/codec.hpp

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+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+namespace codecs {
+
+  class IAudioDecoder {
+    public:
+      virtual ~IAudioDecoder() {}
+
+      virtual auto ProcessData(
+          uint8_t *input,
+          size_t input_len,
+          uint8_t *output) -> size_t = 0;
+  };
+
+} // namespace codecs

src/drivers/include/fatfs_audio_input.hpp

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+#pragma once
+
+namespace drivers {
+
+  class FatfsAudioInput {
+    public:
+      FatfsAudioInput(std::shared_ptr<SdStorage> storage);
+      ~FatfsAudioInput();
+
+      enum Status {
+        /*
+         * Successfully read data into the output buffer, and there is still
+         * data remaining in the file.
+         */
+        OKAY,
+
+        /*
+         * The ringbuffer was full. No data was read.
+         */
+        RINGBUF_FULL,
+
+        /*
+         * Some data may have been read into the output buffer, but the file is
+         * now empty.
+         */
+        FILE_EMPTY,
+      };
+      auto Process() -> Status;
+
+      auto GetOutputBuffer() -> RingbufHandle_t;
+
+    private:
+      std::shared_ptr<SdStorage> storage_;
+      RingbufHandle_t output_;
+
+      std::string path_;
+
+  };
+ 
+} // namespace drivers