The SparkFun MP3 Player Shield is an awesome MP3 decoder with the capabilities of storing music files onto a run-of-the-mill microSD card, thus giving you the ability toadd music or sound effects to any project. With this board you can pull MP3 files from an microSD card and play them using only one shield, effectively turning any Arduino into a fully functional stand-alone MP3 player! The MP3 Shield utilizes the VS1053B MP3 audio decoder IC to decode audio files. The VS1053 is also capable of decoding Ogg Vorbis/MP3/AAC/WMA/MIDI audio and encoding IMA ADPCM and user-loadable Ogg Vorbis.
The VS1053 receives its input bitstream through a serial input bus (SPI). After the stream has been decoded by the IC, the audio is sent out to both a 3.5mm stereo headphone jack, as well as a 2-pin 0.1" pitch header.