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libraries/audio-tools/examples/examples-stream/streams-memory_mp3-pwm/README.md

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+# Decoding a MP3 file
+
+In this example we decode a MP3 file into RAW output and write the output with the help of a PWM signal to the pins. 
+
+Currently we provide multiple mp3 decoders
+- libhelix 
+- tinymp3
+
+Unfortunatly non of those are currently stable in all environments....
+
+
+### Output Device: Earphone
+
+To test the output I am using an earphone from a mobile phone. 
+We get 2 signals one for the left and the other for the right channel.
+
+![DAC](https://pschatzmann.github.io/Resources/img/earphones.jpg)
+
+
+The pins depend on the Processor:
+
+
+| EarPhone   |  ESP32       | RPI Pico      | MBED         |
+| -----------| -------------|---------------|--------------|
+| Left       |  GPI2        | GPI2          | GPI2         |
+| Right      |  GPI3        | GPIO3         | GPI3         |
+| GND        |  GND         | GND           | GND          |
+
+To verify check the PIN_PWM_START in AudioConfig.h or you can set the pins by calling setPins() method on the PWMConfig object.

libraries/audio-tools/examples/examples-stream/streams-memory_mp3-pwm/streams-memory_mp3-pwm.ino

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+/**
+ * @file stream-memory_mp3-analog.ino
+ * @author Phil Schatzmann
+ * @brief decode MP3 stream and output as analog signal
+ * @version 0.1
+ * @date 2021-01-24
+ * 
+ * @copyright Copyright (c) 2021
+ 
+ */
+
+
+#include "AudioTools.h"
+#include "AudioTools/AudioCodecs/CodecMP3Helix.h"
+#include "BabyElephantWalk60_mp3.h"
+
+
+MemoryStream mp3(BabyElephantWalk60_mp3, BabyElephantWalk60_mp3_len);
+PWMAudioOutput out;  // PWM output 
+EncodedAudioStream decoded(&out, new MP3DecoderHelix()); // output to decoder
+StreamCopy copier(decoded, mp3);    // copy in to out
+
+void setup(){
+  Serial.begin(115200);
+  AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Info);  
+
+  // begin processing
+  auto cfg = out.defaultConfig();
+  out.begin(cfg);
+
+  decoded.begin();
+}
+
+void loop(){
+  if (mp3) {
+    copier.copy();
+  } else {
+    auto info = decoded.decoder().audioInfo();
+    LOGI("The audio rate from the mp3 file is %d", info.sample_rate);
+    LOGI("The channels from the mp3 file is %d", info.channels);
+    out.end();
+    stop();
+  }
+}