Repository files navigation

I am providing theHelix MP3 decoder from RealNetworks as a simple Arduino Library. The Helix decoders are based on 16bits integers, so they are a perfect fit to be used in Microcontrollers.

MP3 is a compressed audio file formats based on PCM. A 2.6 MB wav file can be compressed down to 476 kB MP3.

This project can be used stand alone or together with thearduino-audio_tools library. It can also be used from non Arduino based systems with the help of cmake.

The Helix MP3 decoder provides Layer 3 support for MPEG-1, MPEG-2, and MPEG-2.5. It supports variable bit rates, constant bit rates, and stereo and mono audio formats.

The API provides the decoded data to aArduino Stream or alternatively to a callback function. The platform dependent I2S implementations usually implement I2S as subclass of Stream, so you can just provide the corresponding I2S object to the constructor.

Here is a MP3 example using the callback:

#include "MP3DecoderHelix.h"#include "music_mp3.h"using namespace libhelix;void dataCallback(MP3FrameInfo &info, int16_t *pcm_buffer, size_t len, void*) {    for (int i=0; i<len; i+=info.nChans){        for (int j=0;j<info.nChans;j++){            Serial.print(pcm_buffer[i+j]);            Serial.print(" ");        }        Serial.println();    }}MP3DecoderHelix mp3(dataCallback);void setup() {    Serial.begin(115200);    mp3.begin();}void loop() {    Serial.println("writing...");    mp3.write(music_data, music_len);        // restart from the beginning    delay(2000);    mp3.begin();}

For 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/librariesgit clone https://github.com/pschatzmann/arduino-libhelix.git

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

cd arduino-libhelixmkdir buildcd buildcmake ..make

The decoder needs to allocate a buffer to store a frame and the decoded data. The following default values have been defined in ConfigHelix.h:

#define MP3_MAX_OUTPUT_SIZE 1024 * 5#define MP3_MAX_FRAME_SIZE 1024 * 2 #define AAC_MAX_OUTPUT_SIZE 1024 * 8 #define AAC_MAX_FRAME_SIZE 2100

These values are working with standard bitrates, but in some exceptional cases (with extreme (220kbs) or insane (320kbs) bitrates) you might need to increase these values e.g. to

#define MP3_MAX_OUTPUT_SIZE 1024 * 10#define MP3_MAX_FRAME_SIZE 3200

Alternatively you can set the values in your sketch by calling the following methods:

setMaxPCMSize(int size)setMaxFrameSize(int size)

On the ESP32 we support PSRAM: just activate it in the Arduino Tools menu and all the memory will be allocated in PSRAM.

You can define the log level as Debug, Info, Warning, Error

LOGLEVEL_HELIX = LogLevelHelix::Info;

Try to avoid to send metadata to the decoder: in most cases the decoder can automatically ignore invalid mp3 segements, but in some cases itmight not and crash. Use thefunctionality of the AudioTools to filterout the metadata

• TheClass Documentation can be found here
• aacreadme.txt
• mp3readme.txt
• I also suggest that you have a look atmy related blogs

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

This library is based on a adapted version of libhelix fromEarle Phil Hower's ESP8288Audio library
The decoder code is from the Helix project and licensed under RealNetwork'sRPSL license. For commercial use you might still going to need the usual AAC licensing.