MAD from Underbit is a high-quality MPEG audio decoder. It currently supports MPEG-1 and the MPEG-2 extension to lower sampling frequencies, as well as the de facto MPEG 2.5 format. All three audio layers — Layer I, Layer II, and Layer III (i.e. MP3) — are fully implemented. MP3 is a compressed audio file formats based on PCM. A 2.6 MB wav file can be compressed down to 476 kB MP3.

I am providing the MAD MP3 decoder as a Arduino Library with a simple Arduino Style API.

This project can be used stand alone or together with the arduino-audio_tools library. It can also be used outside of Arduino with the help of cmake.

The API provides the decoded data to a Arduino Stream or alternatively to a callback function. Here is a MP3 example using the callback:

#include "MP3DecoderMAD.h"
#include "BabyElephantWalk60_mp3.h"

using namespace libmad;

void pcmDataCallback(MadAudioInfo &info, int16_t *pwm_buffer, size_t len) {
    for (size_t i=0; i<len; i+=info.channels){
        for (int j=0;j<info.channels;j++){
            Serial.print(pwm_buffer[i+j]);
            Serial.print(" ");
        }
        Serial.println();
    }
}

MP3DecoderMAD mp3(pcmDataCallback);

void setup() {
    Serial.begin(115200);
    mp3.begin();
}

void loop() {
    Serial.println("writing...");
    mp3.write(BabyElephantWalk60_mp3, BabyElephantWalk60_mp3_len);    

    // restart from the beginning
    delay(2000);
    mp3.begin();
}

In Arduino, you can download the library as zip and call include Library -> zip library. Or you can git clone this project into the Arduino libraries folder e.g. with

cd  ~/Documents/Arduino/libraries
git clone pschatzmann/arduino-libmad.git

This project can also be built and executed on your desktop with cmake:

cd arduino-libmad
mkdir build
cd build
cmake ..
make

• The Class Documentation can be found here.
• I also suggest that you have a look at my related Blog

I recommend to use this library together with my Arduino Audio Tools. This is just one of many codecs that I have collected so far: Further details can be found in the Encoding and Decoding Wiki of the Audio Tools.