audiomp3 – Support for MP3-compressed audio files

For more information about working with MP3 files in CircuitPython, see this CircuitPython Essentials Learn guide page.

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class audiomp3.MP3Decoder(file: str | BinaryIO, buffer: circuitpython_typing.WriteableBuffer)

Load a mp3 file for audio playback


MP3Decoder uses a lot of contiguous memory, so care should be given to optimizing memory usage. More information and recommendations can be found here:

Load a .mp3 file for playback with audioio.AudioOut or audiobusio.I2SOut.

  • file (Union[str, BinaryIO]) – The name of a mp3 file (preferred) or an already opened mp3 file

  • buffer (WriteableBuffer) – Optional pre-allocated buffer, that will be split in half and used for double-buffering of the data. If not provided, two buffers are allocated internally. The specific buffer size required depends on the mp3 file.

Playback of mp3 audio is CPU intensive, and the exact limit depends on many factors such as the particular microcontroller, SD card or flash performance, and other code in use such as displayio. If playback is garbled, skips, or plays as static, first try using a “simpler” mp3:

  • Use constant bit rate (CBR) not VBR or ABR (variable or average bit rate) when encoding your mp3 file

  • Use a lower sample rate (e.g., 11.025kHz instead of 48kHz)

  • Use a lower bit rate (e.g., 32kbit/s instead of 256kbit/s)

Reduce activity taking place at the same time as mp3 playback. For instance, only update small portions of a displayio screen if audio is playing. Disable auto-refresh and explicitly call refresh.

Playing a mp3 file from flash:

import board
import audiomp3
import audioio
import digitalio

# Required for CircuitPlayground Express
speaker_enable = digitalio.DigitalInOut(board.SPEAKER_ENABLE)

mp3 = audiomp3.MP3Decoder("cplay-16bit-16khz-64kbps.mp3")
a = audioio.AudioOut(board.A0)

while a.playing:
file: BinaryIO

File to play back.

sample_rate: int

32 bit value that dictates how quickly samples are loaded into the DAC in Hertz (cycles per second). When the sample is looped, this can change the pitch output without changing the underlying sample.

bits_per_sample: int

Bits per sample. (read only)

channel_count: int

Number of audio channels. (read only)

rms_level: float

The RMS audio level of a recently played moment of audio. (read only)

samples_decoded: int

The number of audio samples decoded from the current file. (read only)

deinit() None

Deinitialises the MP3 and releases all memory resources for reuse.

__enter__() MP3Decoder

No-op used by Context Managers.

__exit__() None

Automatically deinitializes the hardware when exiting a context. See Lifetime and ContextManagers for more info.

open(filepath: str) None

Takes in the name of a mp3 file, opens it, and replaces the old playback file.