PLAYBACK: Easy to check the recorded file with playback function. When playback, the indicator will be slowly flash to show that the cassette player is operating. You can also copy other MP3 files to USB flash and plug into our device to replay it. Headphone Jack: The cassette to MP3 converter can be used as a portable music player, just plug the 3.55mm/0.1in AUX jack into the converter and use standard headphones to enjoy sound memory.