How to play audio

Applicable for

STM32MP13x lines, STM32MP15x lines, STM32MP25x lines

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1. Article purpose

This article explains how to play audio through the ALSA audio framework in Linux^® OS context. The examples below, show how to play audio on the different audio hardware interfaces of the STM32MPU boards.

2. Audio playback overview

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

Warning

The support of audio output interfaces is board dependent. Please, check available outputs with "aplay -l" command.

The application audio streams are routed by default through the Pipewire sound server. Pipewire exposes audio profiles which are mapped on the ALSA sound card audio devices. The Pipewire server provides a command line interface which allows to list audio profiles and to select a profile, to play on a specific audio interface. The Pipewire sound server keeps a backward compatibility with the former PulseAudio sound server, through the pipewire-pulse package..

Warning

The applications interacting with Weston framework have to be launched as "Weston" user instead of "root" user. The Pulseaudio commands can, for instance, be launched as follows: su -l "weston" -c "pactl info"

The audio playback examples in following sections are given for ALSA utilities. However, the audio playbacks can be launched by other applications, such as gstreamer multimedia framework.

3. Examples

3.1. Audio playback on headset output

3.1.1. Playback on ALSA device

Run audio playback on 'playback_codec' ALSA device:

Information

'playback_codec' is an alias defined in /etc/asound.conf, for headset output device.

 aplay -D playback_codec /usr/share/sounds/alsa/Front_Left.wav

3.1.2. Playback via Pipewire

• Configure Pipewire

Change the Pipewire active profile of the sound card, to 'analog-stereo' profile:

Information

The Pulseaudio analog-stereo profile is the default profile. So next command is not required after boot.

Information

Example below is given for 'alsa_card.platform-sound' soundcard. Check available sound cards and associated output profiles with "pactl list cards" command.

 pactl set-card-profile alsa_card.platform-sound output:analog-stereo

• Run audio playback:

Information

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

 aplay /usr/share/sounds/alsa/Front_Left.wav

3.2. Audio playback on HDMI output

Warning

The support of HDMI output is board dependent. Please, check available outputs with "aplay -l" command.

3.2.1. Playback on ALSA device

Run audio playback on 'playback_hdmi' ALSA device:

Information

'playback_hdmi' is an alias defined in /etc/asound.conf, for hdmi output device.

 aplay -D playback_hdmi /usr/share/sounds/alsa/Front_Left.wav

3.2.2. Playback via PulseAudio

• Configure Pulseaudio

Change the Pulseaudio active profile of the sound card, to 'hdmi-stereo' profile:

Information

Example below is given for 'alsa_card.platform-sound' soundcard. Check available sound cards and associated output profiles with "pactl list cards" command.

 pactl set-card-profile alsa_card.platform-sound output:hdmi-stereo

• Run audio playback:

 aplay /usr/share/sounds/alsa/Front_Left.wav

3.3. Audio playback on S/PDIF output

Information

S/PDIF ALSA device supports only 32-bit audio streams. As 32-bit wave files are not provided in sample sound files, speaker-test is used instead of aplay, for convenience, here. Speaker-test generates a 440Hz sine wave in following examples.

3.3.1. Set IEC958 status bits

Information

Example below is given for sound card index 0. Check sound card index with "aplay -l" command.

Example: set IEC958 mode bit.

 iecset -c 0 -n device=0 pro on

3.3.2. Playback on ALSA device

Run audio playback on 'playback_spdif' ALSA device:

Information

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

 speaker-test -D playback_spdif --channels 2 --format S32_LE -f 440 -t sine -l 1

3.3.3. Playback via PulseAudio

• Configure Pulseaudio

Change the sound card active profile, to S/PDIF 'iec958-stereo' profile.

Information

Example below is given for 'alsa_card.platform-sound' soundcard. Check available sound cards and associated output profiles with "pactl list cards" command.

 pactl set-card-profile alsa_card.platform-sound output:iec958-stereo

• Run audio playback:

 speaker-test --channels 2 --format S32_LE -f 440 -t sine -l 1

Linux^® is a registered trademark of Linus Torvalds.

Operating system

Advanced Linux sound architecture

High-definition multimedia interface (HDMI standard)

Sony/Philips digital interface format (Protocol (IEC-60958))