Play MP3 files from SD card using Maker Pi Pico and CircuitPython

code.py

"""
  Play MP3 files from SD card using Maker Pi Pico and CircuitPython
  
  Maker Pi Pico
  - https://my.cytron.io/p-maker-pi-pico
  6W Stereo USB Powered 3.5mm Jack Speaker
  - https://my.cytron.io/p-6w-stereo-usb-powered-3-5mm-jack-speaker-black
  Dual 18650 Dual Output 3.3V and 5V USB Module (optional)
  - https://my.cytron.io/c-lithium-ion-rechargeable-battery-and-charger
  3.7V 2000mAh Li-Ion Battery
  - https://my.cytron.io/p-3.7v-2000mah-li-ion-battery
  
  References:
  - https://learn.adafruit.com/adafruit-microsd-spi-sdio
  
  Last Modified: 5 Dec 2021
"""

import os
import time
import board
import digitalio
import busio
import sdcardio
import storage

from audiomp3 import MP3Decoder # pylint: disable=wrong-import-position

try:
    from audioio import AudioOut
except ImportError:
    try:
        from audiopwmio import PWMAudioOut as AudioOut
    except ImportError:
        pass  # not always supported by every board!

led = digitalio.DigitalInOut(board.LED)
led.direction = digitalio.Direction.OUTPUT

button1 = digitalio.DigitalInOut(board.GP20)
button1.direction = digitalio.Direction.INPUT

button2 = digitalio.DigitalInOut(board.GP21)
button2.direction = digitalio.Direction.INPUT

spi = busio.SPI(board.GP10, board.GP11, board.GP12)
sd = sdcardio.SDCard(spi, board.GP15)
vfs = storage.VfsFat(sd)
storage.mount(vfs, '/sd')

mp3files = sorted("/sd/" + filename for filename in os.listdir("/sd")
    if filename.lower().endswith("mp3"))

# You have to specify some mp3 file when creating the decoder
mp3 = open(mp3files[0], "rb")
decoder = MP3Decoder(mp3)
audio = AudioOut(board.GP18, right_channel=board.GP19)

while True:
    if button1.value == False:
        filename = mp3files[0]
        print("Playing", filename)

        # Updating the .file property of the existing decoder
        # helps avoid running out of memory (MemoryError exception)
        decoder.file = open(filename, "rb")
        audio.play(decoder)

        while button1.value == False:
            continue

        while audio.playing:
            if button1.value == False:
                print("Stop", filename)
                audio.stop()

                while button1.value == False:
                    continue

                break

    if button2.value == False:
        filename = mp3files[1]
        print("Playing", filename)

        # Updating the .file property of the existing decoder
        # helps avoid running out of memory (MemoryError exception)
        decoder.file = open(filename, "rb")
        audio.play(decoder)

        while button2.value == False:
            continue

        while audio.playing:
            if button2.value == False:
                print("Stop", filename)
                audio.stop()

                while button2.value == False:
                    continue

                break

Do I have to replace the "rb" with the mp3 file name? It says:
Traceback (most recent call last):
File "", line 55, in
ValueError: Invalid mode

How do I fix this?

@zen375dragon Old question, but if you stopped on this project, rb stands for Read Binary. This just means that when you open the mp3 file, you're only reading it, not writing to the file, so you leave that alone.

Error on line 55 means you don't have any mp3 files found at that path. Path should be sd/whatever.mp3. This code looks for all files that end with .mp3 in the sd folder. Since none were found, that's why you got the error.