Hello, first, I am not very familiar with C language...
I can't find a way to use the function loadUserCode. it is declared as protected, when I tried to call it from my sketch, of course, I have an error:
error: 'void VS1003::loadUserCode(const uint16_t*, size_t) const' is protected.
An exemple to use this function would be welcome...

here the code producing the error:
#include <VS1003.h>

extern const uint16_t pluginfft[];
extern const size_t PLUGIN_SIZE;

VS1003 player(9, 6, 7, 8); // cs_pin, dcs_pin, dreq_pin, reset_pin

void setup()
{
player.loadUserCode(pluginfft,PLUGIN_SIZE);
}
void loop()
{
}

error: 'void VS1003::loadUserCode(const uint16_t*, size_t) const' is protected
void loadUserCode(const uint16_t* buf, size_t len) const;
^
/Users/xxx/Dossiers/Arduino/VS1003FFT/VS1003FFT.ino:14:45: error: within this context
player.loadUserCode(pluginfft,PLUGIN_SIZE);