[audio] Add support for sinking via an arbitrary callback (#14035)

esphome/components/audio/audio_transfer_buffer.cpp

@@ -165,6 +165,8 @@ size_t AudioSinkTransferBuffer::transfer_data_to_sink(TickType_t ticks_to_wait,
         if (this->ring_buffer_.use_count() > 0) {
       bytes_written =
           this->ring_buffer_->write_without_replacement((void *) this->data_start_, this->available(), ticks_to_wait);
+    } else if (this->sink_callback_ != nullptr) {
+      bytes_written = this->sink_callback_->audio_sink_write(this->data_start_, this->available(), ticks_to_wait);
     }
 
     this->decrease_buffer_length(bytes_written);

esphome/components/audio/audio_transfer_buffer.h

@@ -15,6 +15,12 @@
 namespace esphome {
 namespace audio {
 
+/// @brief Abstract interface for writing decoded audio data to a sink.
+class AudioSinkCallback {
+ public:
+  virtual size_t audio_sink_write(uint8_t *data, size_t length, TickType_t ticks_to_wait) = 0;
+};
+
 class AudioTransferBuffer {
   /*
    * @brief Class that facilitates tranferring data between a buffer and an audio source or sink.
@@ -108,6 +114,10 @@ class AudioSinkTransferBuffer : public AudioTransferBuffer {
   void set_sink(speaker::Speaker *speaker) { this->speaker_ = speaker; }
 #endif
 
+  /// @brief Adds a callback as the transfer buffer's sink.
+  /// @param callback Pointer to the AudioSinkCallback implementation
+  void set_sink(AudioSinkCallback *callback) { this->sink_callback_ = callback; }
+
   void clear_buffered_data() override;
 
   bool has_buffered_data() const override;
@@ -116,6 +126,7 @@ class AudioSinkTransferBuffer : public AudioTransferBuffer {
 #ifdef USE_SPEAKER
   speaker::Speaker *speaker_{nullptr};
 #endif
+  AudioSinkCallback *sink_callback_{nullptr};
 };
 
 class AudioSourceTransferBuffer : public AudioTransferBuffer {