How to record audio: Difference between revisions

Latest revision as of 14:47, 23 October 2024↑

Applicable for

STM32MP13x lines, STM32MP15x lines, Unknown MPU, STM32MP25x lines

1. Article purpose[edit | edit source]↑

This article explains how to record audio via the kernel ALSA audio framework in Linux® OS context. The examples below, show how to record audio from the different audio hardware interfaces of the STM32MPU boards.

2. Audio record overview[edit | edit source]↑

The ALSA framework exposes audio devices associated to the board audio hardware interfaces.

Warning

The support of audio input interfaces is board dependent. Please, check available inputs using the "arecord -l" command.

The application audio streams are routed by default through the Pipewire^[1] sound server. Pipewire exposes audio profiles, which are mapped on the ALSA sound card audio devices. The Pipewire server provides a command line interface to list audio profiles and to select one, in order to record from a specific audio interface.

Information

In this article, the PulseAudio 'pactl' command is used in the examples. This is possible because the PipeWire sound server maintains backward compatibility with the former PulseAudio sound server through the pipewire-pulse package.

Warning

The applications that interact with the Weston framework have to be launched as "Weston" user instead of "root" user. The Pulseaudio commands, for instance, can be launched as follows:

su -l "weston" -c "pactl info"

The audio record examples in following sections are based on ALSA utilities. Some input paths are configured through ALSA controls. These configurations are detailed in sound card configuration article. If an error is issued when running an example, please refer to Audio troubleshooting grid article for debug.

3. Examples[edit | edit source]↑

3.1. Audio record from headset microphone input[edit | edit source]↑

3.1.1. Record from ALSA device[edit | edit source]↑

Start audio record from 'record_codec' ALSA device:

Information

'record_codec' is an alias defined in /etc/asound.conf, for headset microphone input device.

arecord -D record_codec -f S16_LE -d 10 /tmp/rec.wav

3.1.2. Record via Pipewire[edit | edit source]↑

Configure Pipewire :

Change Pulseaudio default input source to 'analog_input':

Information

The Pulseaudio analog_input is defined in /etc/pipewire/pipewire-pulse.conf.d/system.pa.conf configuration file.

pactl set-default-source analog_input

Start audio record :

Information

The Pipewire device is the default one, so "-D pipewire" option can be omitted in the record command.

arecord -d 10 /tmp/rec.wav

3.2. Audio record from digital microphone input[edit | edit source]↑

3.2.1. Record from ALSA device[edit | edit source]↑

Start mono audio record from 'record_dmic0' ALSA device:

Information

'record_dmic0' is an alias defined in /etc/asound.conf, for digital microphone U1 input device.

arecord -D record_dmic0 --rate 16000 --format S32_LE --channels 1 -d 10 /tmp/rec.wav

3.2.2. Record multiple digital microphones from a virtual ALSA device[edit | edit source]↑

Start stereo audio record from 'multi' ALSA device:

Information

'multi' device, based on ALSA multi plugin^[2], has to be defined in /etc/asound.conf file.

arecord -D multi --rate 16000 --format S32_LE --channels 2 -d 10 /tmp/rec.wav

3.2.3. Record via Pipewire[edit | edit source]↑

Configure Pipewire

Change Pulseaudio default input source to 'dmic1_input':

Information

The Pulseaudio dmic1_input is defined in /etc/pipewire/pipewire-pulse.conf.d/system.pa.conf configuration file.

pactl set-default-source dmic1_input

Start audio record :

Information

The Pipewire device is the default one, so "-D pipewire" option can be omitted in the record command.

arecord -r 48000 -f S32_LE -c 2 -d 10 /tmp/rec.wav

3.3. Audio record from S/PDIF input[edit | edit source]↑

3.3.1. Get IEC958 status bits[edit | edit source]↑

Some restrictions may apply to IEC958 control, depending on the SPDIFRX device configuration as it is explained in SPDIFRX device tree configuration and SPDIFRX Linux driver articles.

Information

The example below is given for sound card index 0. Check sound card index using the "aplay -l" command.

amixer -c 0 cget iface=PCM,name='IEC958 Capture Default'

3.3.2. Record from ALSA device[edit | edit source]↑

Start audio record from 'record_spdif' ALSA device:

Information

'record_spdif' is an alias defined in /etc/asound.conf, for S/PDIF input device.

Information

A S/PDIF signal must be available on S/PDIF RCA input connector before starting the record command. The record rate must be set according to S/PDIF signal sampling rate.

arecord -D record_spdif --rate 48000 --format S32_LE --channels 2 -d 10 /tmp/rec.wav

3.3.3. Record via Pipewire[edit | edit source]↑

Configure Pipewire

Change Pulseaudio default input source to 'iec958_input':

Information

The Pulseaudio iec958_input is defined in /etc/pipewire/pipewire-pulse.conf.d/system.pa.conf configuration file.

pactl set-default-source iec958_input

Start audio record :

Information

The Pipewire device is the default one, so "-D pipewire" option can be omitted in the record command.

arecord --rate 48000 --format S32_LE --channels 2 -d 10 /tmp/rec.wav

4. References[edit | edit source]↑

[1] Pipewire documentation

[2] ALSA PCM plugins

[1]

[2]

@@ Line 1: / Line 1: @@
 {{ApplicableFor
-|MPUs list=STM32MP13x, STM32MP15x, STM32MP25x
+|MPUs list=STM32MP13x, STM32MP15x, STM32MP21x, STM32MP25x
-|MPUs checklist=STM32MP13x, STM32MP15x, STM32MP25x
+|MPUs checklist=STM32MP13x, STM32MP15x, STM32MP21x, STM32MP23x, STM32MP25x
 }}
 <noinclude></noinclude>
@@ Line 12: / Line 12: @@
 {{Warning|The support of audio input interfaces is board dependent. Please, check available inputs using the "''arecord -l''" command.}}
-The application audio streams are routed by default through the PulseAudio sound server. PulseAudio exposes audio profiles, which are mapped on the ALSA sound card audio devices. The PulseAudio server provides a command line interface to list audio profiles and to select one, in order to record from a specific audio interface.
+The application audio streams are routed by default through the Pipewire<ref>[https://docs.pipewire.org/ Pipewire documentation]</ref> sound server. Pipewire exposes audio profiles, which are mapped on the ALSA sound card audio devices. The Pipewire server provides a command line interface to list audio profiles and to select one, in order to record from a specific audio interface.
+{{info | In this article, the PulseAudio 'pactl' command is used in the examples. This is possible because the PipeWire sound server maintains backward compatibility with the former PulseAudio sound server through the pipewire-pulse package.}}
 {{Warning|The applications that interact with the Weston framework have to be launched as "Weston" user instead of "root" user. The Pulseaudio commands, for instance, can be launched as follows:
@@ Line 28: / Line 30: @@
 {{Info|'record_codec' is an alias defined in /etc/asound.conf, for headset microphone input device.}}
-  {{Board$}} arecord -D record_codec -f S16_LE -d 10 /tmp/rec.wav
+  {{Board$}}arecord -D record_codec -f S16_LE -d 10 /tmp/rec.wav
-==== Record via PulseAudio ====
+==== Record via Pipewire ====
-* '''Configure Pulseaudio :'''
+* '''Configure Pipewire :'''
 Change Pulseaudio default input source to 'analog_input':
-{{Info|The Pulseaudio analog_input is defined in /etc/pulse/system.pa configuration file.}}
+{{Info|The Pulseaudio analog_input is defined in /etc/pipewire/pipewire-pulse.conf.d/system.pa.conf configuration file.}}
-  {{Board$}} pactl set-default-source analog_input
+  {{Board$}}pactl set-default-source analog_input
 * '''Start audio record :'''
-{{Info|The Pulseaudio device is the default one, so "-D pulse" option can be omitted in the record command.}}
+{{Info|The Pipewire device is the default one, so "-D pipewire" option can be omitted in the record command.}}
-  {{Board$}} arecord -d 10 /tmp/rec.wav
+  {{Board$}}arecord -d 10 /tmp/rec.wav
 === Audio record from digital microphone input ===
@@ Line 46: / Line 48: @@
 Start mono audio record from 'record_dmic0' ALSA device:
 {{Info|'record_dmic0' is an alias defined in /etc/asound.conf, for digital microphone U1 input device.}}
-  {{Board$}} arecord -D record_dmic0 --rate 16000 --format S32_LE --channels 1 -d 10 /tmp/rec.wav
+  {{Board$}}arecord -D record_dmic0 --rate 16000 --format S32_LE --channels 1 -d 10 /tmp/rec.wav
 ==== Record multiple digital microphones from a virtual ALSA device ====
 Start stereo audio record from 'multi' ALSA device:
 {{Info|'multi' device, based on ALSA multi plugin<ref>[https://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html ALSA PCM plugins]</ref>, has to be defined in /etc/asound.conf file.}}
-  {{Board$}} arecord -D multi --rate 16000 --format S32_LE --channels 2 -d 10 /tmp/rec.wav
+  {{Board$}}arecord -D multi --rate 16000 --format S32_LE --channels 2 -d 10 /tmp/rec.wav
-==== Record via PulseAudio ====
+==== Record via Pipewire ====
-* '''Configure Pulseaudio'''
+* '''Configure Pipewire'''
 Change Pulseaudio default input source to 'dmic1_input':
-{{Info|The Pulseaudio dmic1_input is defined in /etc/pulse/system.pa configuration file.}}
+{{Info|The Pulseaudio dmic1_input is defined in /etc/pipewire/pipewire-pulse.conf.d/system.pa.conf configuration file.}}
-  {{Board$}} pactl set-default-source dmic1_input
+  {{Board$}}pactl set-default-source dmic1_input
 * '''Start audio record :'''
-{{Info|The Pulseaudio device is the default one, so "-D pulse" option can be omitted in the record command.}}
+{{Info|The Pipewire device is the default one, so "-D pipewire" option can be omitted in the record command.}}
-  {{Board$}} arecord -r 48000 -f S32_LE -c 2 -d 10 /tmp/rec.wav
+  {{Board$}}arecord -r 48000 -f S32_LE -c 2 -d 10 /tmp/rec.wav
 === Audio record from S/PDIF input ===
@@ Line 70: / Line 72: @@
 {{Info|The example below is given for {{highlight|sound card index 0}}. Check sound card index using the "''aplay -l''" command.}}
-  {{Board$}} amixer -c 0 cget iface=PCM,name='IEC958 Capture Default'
+  {{Board$}}amixer -c 0 cget iface=PCM,name='IEC958 Capture Default'
 ==== Record from ALSA device ====
@@ Line 76: / Line 78: @@
 {{Info|'record_spdif' is an alias defined in /etc/asound.conf, for S/PDIF input device.}}
 {{Info|A S/PDIF signal must be available on S/PDIF RCA input connector before starting the record command. The record rate must be set according to S/PDIF signal sampling rate.}}
-  {{Board$}} arecord -D record_spdif --rate 48000 --format S32_LE --channels 2 -d 10 /tmp/rec.wav
+  {{Board$}}arecord -D record_spdif --rate 48000 --format S32_LE --channels 2 -d 10 /tmp/rec.wav
-==== Record via PulseAudio ====
+==== Record via Pipewire ====
-* '''Configure Pulseaudio'''
+* '''Configure Pipewire'''
 Change Pulseaudio default input source to 'iec958_input':
-{{Info|The Pulseaudio iec958_input is defined in /etc/pulse/system.pa configuration file.}}
+{{Info|The Pulseaudio iec958_input is defined in /etc/pipewire/pipewire-pulse.conf.d/system.pa.conf configuration file.}}
-  {{Board$}} pactl set-default-source iec958_input
+  {{Board$}}pactl set-default-source iec958_input
 * '''Start audio record :'''
-{{Info|The Pulseaudio device is the default one, so "-D pulse" option can be omitted in the record command.}}
+{{Info|The Pipewire device is the default one, so "-D pipewire" option can be omitted in the record command.}}
-  {{Board$}} arecord --rate 48000 --format S32_LE --channels 2 -d 10 /tmp/rec.wav
+  {{Board$}}arecord --rate 48000 --format S32_LE --channels 2 -d 10 /tmp/rec.wav
 == References ==