Arduino AAC Encoding and Decoding Library

I was looking for a way to encode sound PCM data to the AAC or MPEG data format on some Arduino Devices. That's when I found the Fraunhofer FDK AAC library.

The Android-targeted implementation of the Fraunhofer AAC can be used for encoding and decoding, uses fixed-point math and is optimized for encoding on embedded devices/mobile phones. The library is currently limited to 16-bit PCM input. So this seems to be the perfect match to be used in Arduino based Microcontrollers.

I have forked the fdk-aac project, converted it to an Arduino library and provided a simple Arduino friendly API. The only caveat is, that I have removed all optimized processor specific assembler code (e.g. for ARM, 386 and mips), so that it will compile with the same code on all Arduino environements.

Decoding Example

#include "AACDecoderFDK.h"
#include "BabyElephantWalk60_aac.h"

SET_LOOP_TASK_STACK_SIZE(50 * 1024);  

using namespace aac_fdk;


void dataCallback(CStreamInfo &info, INT_PCM *pcm_data, size_t len) {
    int channels = info.numChannels;
    for (size_t i=0; i<len; i+=channels){
        for (int j=0;j<channels;j++){
            Serial.print(pcm_data[i+j]);
            Serial.print(" ");
        }
        Serial.println();
    }
}

AACDecoderFDK aac(dataCallback);

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

void loop() {
    Serial.println("writing...");
    aac.write(BabyElephantWalk60_aac, BabyElephantWalk60_aac_len);    

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

Encoding Example

#include "AACEncoderFDK.h"
#include <stdlib.h>     /* srand, rand */

using namespace aac_fdk;

void dataCallback(uint8_t *aac_data, size_t len) {
    Serial.print("AAC generated with ");
    Serial.print(len);
    Serial.println(" bytes");
}

AACEncoderFDK aac(dataCallback);
AudioInfo info;
int16_t buffer[512];

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

    info.channels = 1;
    info.sample_rate = 10000;
    aac.begin(info);
}

void loop() {
    Serial.println("writing 512 samples of random data");
    for (int j=0;j<512;j++){
        buffer[j] = (rand() % 100) - 50;         
    }
    aac.write(buffer, 512);
}

Logging

The log level can be defined with the help of the global LOGLEVEL_FDK variable. By default it is set to FDKWarning. You can change it by calling e.g.

LOGLEVEL_FDK = FDKInfo;

Installation

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/libraries
git clone https://github.com/pschatzmann/codec-fdk-aac.git

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

cd codec-fdk-aac
mkdir build
cd build
cmake ..
make

Documentation

• The generated 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.

Compile Issues / Supported Architectures

On some processors we get compile errors because the arrays are too big: Please uncomment the #define PIT_MAX_MAX line in the AACConstantsOverride.h file.

The encoder is working on an ESP32 w/o PSRAM. The Decoder however needs PSRAM and a 50kbytes stack size!

Copyright

Please read the included NOTICE.