File* pFile = nullptr;
AudioSourceIdxSDMMC source("/","mp3",true);
...
pFile = (File*)source.selectStream("/test.mp3"); 
...
MP3DecoderHelix decoderMP3;
MetaDataFilterDecoder metadatafilter(decoderMP3);
MeasuringStream measureMP3(decoderMP3);
...
measureMP3.begin();
decoderMP3.begin();
player.setDecoder(metadatafilter);
player.begin();
...
while (playing)
{
 sMP3_begin = measureMP3.estimatedTotalTimeFor(pFile->size());
 Serial.println(sMP3_begin);
 player.copy();
}