add mp3 player code

Code/MP3Player/mp3_decoder_task.h

@@ -0,0 +1,39 @@
+#ifndef MP3_DECODER_TASK_H
+#define MP3_DECODER_TASK_H
+
+#include <cstdint>
+#include "config.h"
+#include "pcm_audio_interface.h"
+#include "sd_reader_task.h"
+#include "gpio_rp2040.h"
+#include "task.h"
+#include "mad.h"
+
+class mp3_decoder_task : public task
+{
+public:
+    mp3_decoder_task(pcm_audio_interface & pcm_if, sd_reader_task & sd);
+
+    void run() override;
+    void reset();
+    uint16_t  get_position(unsigned long fsize,int max_pos);
+    uint32_t get_total_seconds();
+private:
+    static enum mad_flow input (void *data, struct mad_stream *stream);
+    static enum mad_flow header(void *data, struct mad_header const *);
+    static enum mad_flow output(void *data, mad_header const *header, mad_pcm *pcm);
+    static enum mad_flow error (void *data, mad_stream *stream, mad_frame *frame);
+    static int16_t       scale (mad_fixed_t sample);
+
+    pcm_audio_interface &   _pcm_if;
+    sd_reader_task  &       _sd_reader;
+    mad_decoder             _decoder{};
+    gpio_rp2040_pin         _led;
+    uint8_t                 _mp3_buf[MP3_BUF_SIZE]{};
+    uint32_t                _pcm_rate;
+    mad_timer_t             _timer;
+    unsigned long           _bitrate;
+    unsigned long           _total_time;
+};
+
+#endif // MP3_DECODER_TASK_H