The most reliable method is a 3.5mm auxiliary cable plugged into your head unit's AUX-in port, which gives you direct audio output from the MP3 player with no signal loss or pairing delays.

If your head unit lacks an AUX input — common on factory radios from the mid-2000s and earlier — an FM transmitter plugs into the MP3 player's headphone jack and broadcasts over a local FM frequency your radio tunes to, though audio quality is noticeably lower than a wired connection. METEESER Android head units include a USB input that can charge and play audio from an MP3 player simultaneously, and Bluetooth pairing is available on units running Android 13 if the MP3 player supports A2DP audio streaming.

  • AUX cable connection: standard 3.5mm TRS male-to-male, works on any head unit with a 3.5mm AUX-in port.
  • FM transmitter frequency range: 87.5–108.0 MHz; audio quality degrades proportionally to local station interference.
  • USB audio playback on METEESER Android 13 head units supports MP3, WMA, FLAC, and WAV file formats.
  • Bluetooth A2DP streaming requires the MP3 player to have built-in Bluetooth — most basic MP3 players do not.
  • METEESER double-DIN units include one front USB port and one rear USB port for media and device connections.

How to Choose

  • Use an AUX cable if: your head unit has a 3.5mm AUX-in port — best audio quality, no setup, zero latency.
  • Use USB playback on a METEESER Android 13 head unit if: your MP3 files are stored on a device or flash drive and you want simultaneous charging while playing FLAC or WAV losslessly.
  • Use an FM transmitter if: your factory radio has no AUX input and no USB port — expect noticeable audio quality drop, especially in dense urban areas with crowded FM bands.
  • Use Bluetooth A2DP if: your MP3 player has built-in Bluetooth and you want a cable-free connection — confirm A2DP support on the player before assuming it pairs.