class PCM - Audio Coding

2026-05-21

This class provides read and write interfaces for PCM audio data, the PCM data can be used for audio encoding.

All models that support audio also support PCM.

Create Object

`audio.Audio.PCM`

class audio.Audio.PCM(mic_dev, channel, samplerate, flag，mode， periodcnt)

Create an Audio object.

Parameter Description:

For detailed parameter descriptions, please refer to the table below

Parameter	Parameter Type	Description
`mic_dev`	int	mic channel: `0` - earpiece `1` - headset `2` - auto
`channel`	int	Number of channels: `1` :mono( PCM.MONO) `2` :stereo (PCM.STEREO)
`samplerate`	int	Sampling rate: 8000, 16000
`flag`	int	Mode: `0` :read only(PCM.READONLY) `1` :write only(PCM.WRITEONLY) `2` :read/write(PCM.WRITEREAD)
`mode`	int	Blocking mode (default = 1): `1` :blocking(PCM.BLOCK) `2` :non‑blocking(PCM.NOBLOCK)
`periodcnt`	int	Buffer size in frames.Range: `[2,25]` Unit: frame. 20 ms per frame. Default = 3,(meaning up to 3 frames of data are stored by default.)

example:

from audio import Audio
pcm = Audio.PCM(1, Audio.PCM.MONO, 8000, Audio.PCM.WRITEREAD, Audio.PCM.BLOCK)

Method

`PCM.read`

PCM.read(size)

This method is used to read the PCM data of the module's MIC recording.

Parameter Description:

size - Maximum amount of data read, of type int, with the unit of ByteDance. (The amount of data read in a single operation does not exceed the size of the set buffer buf)

Note: The recording time can be calculated based on the sampling rate, number of channels, and sampling precision. The specific calculation formula is:

Time(s) = Amount of data to be obtained (byte) / (Sampling rate (hz) * Number of channels (channel) * Sampling precision (byte/sample) )

For example: Set the sampling rate to 8000, mono, and want to read data with size = 320. The PCM sampling precision of the module is 2, so the recording time of this interface is 0.02s

Return value description:

Successfully returned data buffer;
Returns -1 if it fails.

`PCM.write`

PCM.write(buff)

This method is used to write PCM data that will be played.

Parameter Description:

buff - PCM data to be written, of type bytearray.

Return value description:

Successfully returns the amount of data written;
Returns -1 if it fails.

Example:

from audio import Audio
pcm = Audio.PCM(1, Audio.PCM.MONO, 8000, Audio.PCM.WRITEREAD, Audio.PCM.BLOCK)

pcm_buf = pcm.read(320)
pcm.write(pcm_buf)

`PCM.close`

PCM.close()

This method is used to close PCM and release the corresponding resources.

Return value description:

0 indicates success, -1 indicates failure.

`PCM.setVolume`

PCM.setVolume(vol)

This method is used to set the playback volume, with the volume value in the range [0, 11], where 0 indicates mute.

Parameter Description:

vol - Volume level, int type, range [0, 11].

Return value description:

0 indicates success, -1 indicates failure.

Note: This method sets the audio playback volume, which has the same effect as Audio.setVolume in setting the volume.

`PCM.getVolume`

PCM.getVolume()

This method is used to obtain the current playback volume level, with the volume value in the range [0, 11], where 0 represents mute.

Return value description:

Integer volume value.

Audio Encoding - G711

This module is used for recording and audio playback in G711 format.

Constructor function

class G711(pcm)

Create a G711 object.

Parameter Description:

device - PCM object, obj type, see [PCM](#Create Object) . (G711 only supports 8K sampling rate by default, please note this issue when creating a PCM object)

Example:

import G711
import audio

pcm = audio.Audio.PCM(0, 1, 8000, 2)
g711 = G711(pcm)

`G711.read`

This method is used to read G711 format recording data, outputting one frame of recording data at a time (one frame of recording time is 20ms, and the data length is 160 ByteDance at 8k sampling rate).

G711.read(format)

Parameter Description:

format - Encoding format, int type, 0 : A-LAW, 1 : U-LAW.

Return value description:

If successful, return the audio buffer;

Returns -1 if it fails.

Note: Usually, after PCM data is encoded in G711 format, the data volume is only 1/2 of the original; conversely, after G711 is decoded to PCM, the data volume is twice the original.

`G711.write`

This method is used to decode G711 audio data and play it.

G711.write(buffer, format)

Parameter Description:

format - Encoding format of audio data, int type, 0 : A-LAW, 1 : U-LAW.
buff - Audio data to be decoded, of type bytearray.

Return value description:

Successfully returns the decoded data volume written;
Returns -1 if it fails.

Example:

import G711
import audio
import uos

pcm = audio.Audio.PCM(0, 1, 8000, 2)
g711 = G711(pcm)
#g711 code
def g711_compress(frame):
    f = open("/usr/test.g711", "wb")
    count = frame
    while count:
        count-=1
        g711_buf = g711.read(0)
        print("len:",len(g711_buf))
        if(len(g711_buf) > 0):
            f.write(g711_buf)
    f.close()
#g711 decode
def g711_decompression():
    file_size = uos.stat("/usr/test.g711")[6]  # get file size
    print(file_size)
    with open("/usr/test.g711", "rb")as f:   
        while 1:
            b = f.read(320)
            if not b:
                break
            write_len = g711.write(b, 0)
        f.close()

if __name__ == "__main__":
    g711_compress(200)
    g711_decompression()

Audio Encoding - G722

This module is used for recording and audio playback in G722 format.

Constructor function

class G722(pcm, bitrate)

Create a G722 object.

Parameter Description:

device - PCM object, obj type, see [PCM](#Create Object). (G722 supports 16K sampling rate by default, please note this issue when creating a PCM object)
bitrate - Bitrate, int type, optional values: 64000 , 56000 , 48000 .

Example:

import G722
import audio

pcm = audio.Audio.PCM(0, 1, 16000, 2)
g722 = G722(pcm, 64000)

G722.read

This method is used to read G722 format recording data, outputting one frame of recording data at a time (one frame of recording time is 20ms, and the data length is 160 bytes at a 16k sampling rate).

G722.read()

Return value description:

If successful, return the audio buffer;

If it fails, an error will be reported directly.

Note: Usually, after PCM data is encoded using G722, the data volume is only 1/4 of the original; conversely, after G722 is decoded to PCM, the data volume is 4 times the original.

`G722.write`

This method is used to decode G722 audio data into PCM and place it in the playback buffer for playback.

G722.write(buffer)

Parameter Description:

buff - Audio data to be decoded, of type bytearray.

Return value description:

Successfully returns the amount of data written;
Returns -1 if it fails.

Example:

import audio
import G722
import uos

pcm = audio.Audio.PCM(0, 1, 16000, 2, 1)
g722 = G722(pcm, 64000)
#g722 code
def g722_compress(frame):
    f = open("/usr/test.g722", "wb")
    count = frame
    while count:
        count-=1
        g722_buf = g722.read()
        print("len:",len(g722_buf))
        if(len(g722_buf) > 0):
            f.write(g722_buf)
    f.close()
#g722 decode
def g722_decompression():
    file_size = uos.stat("/usr/test.g722")[6]  # get file size
    print("size=",file_size)
    with open("/usr/test.g722", "rb")as f:   
        while 1:
            b = f.read(160)
            if not b:
                break
            write_len = g722.write(b)
        f.close()

if __name__ == "__main__":
    g722_compress(200)
    g722_decompression()

Audio Encoding - G729

This module is used for recording and audio playback in G729 format.

Constructor function

class G729(pcm)

Create a G729 object. (G729 supports the 8K sampling rate by default, so please note this issue when creating a PCM object)

Parameter Description:

device - PCM object, obj type, see [PCM](#Create Object) .

Example:

import G729
import audio

pcm = audio.Audio.PCM(0, 1, 8000, 2)
g729 = G729(pcm)

`G729.read`

This method is used to read G722 format recording data, outputting one frame of recording data at a time (the length of one frame of recording data is 20 bytes).

G729.read()

Return value description:

If successful, return the audio buffer;

If it fails, an error will be reported directly.

Note: Usually, after PCM data is encoded using G729, the data volume is only 1/16 of the original; conversely, after G729 is decoded into PCM, the data volume is 16 times the original.

`G729.write`

This method is used to decode G729 audio data into PCM and place it in the playback buffer for playback.

G729.write(buffer)

Parameter Description:

buff - Audio data to be decoded, of type bytearray.

Return value description:

Successfully returns the amount of data written;

Returns -1 if it fails.

Example:

import audio
import G729
import uos

pcm = audio.Audio.PCM(0, 1, 8000, 2, 1)
g729 = G729(pcm)
#g729 code
def g729_compress(frame):
    f = open("/usr/test.g729", "wb")
    count = frame
    while count:
        count-=1
        g729_buf = g729.read()
        print("len:",len(g729_buf))
        if(len(g729_buf) > 0):
            f.write(g729_buf)
    f.close()
#g729 decode
def g729_decompression():
    file_size = uos.stat("/usr/test.g729")[6]  # get file size
    print("size=",file_size)
    with open("/usr/test.g729", "rb")as f:   
        while 1:
            b = f.read(20)
            if not b:
                break
            write_len = g729.write(b)
        f.close()

if __name__ == "__main__":
    g729_compress(200)
    g729_decompression()

Record - Audio Record

qrcode - QR Code Display

QuecPython

class PCM - Audio Coding

Create Object

audio.Audio.PCM

Method

PCM.read

PCM.write

PCM.close

PCM.setVolume

PCM.getVolume

Audio Encoding - G711

Constructor function

G711.read

G711.write

Audio Encoding - G722

Constructor function

G722.read

G722.write

Audio Encoding - G729

Constructor function

G729.read

G729.write

`audio.Audio.PCM`

`PCM.read`

`PCM.write`

`PCM.close`

`PCM.setVolume`

`PCM.getVolume`

`G711.read`

`G711.write`

`G722.write`

`G729.read`

`G729.write`