Linux Multimedia

Linux
Audio
Video
Published

September 14, 2014

Modified

February 28, 2023

Audio

ALSA

ALSA (Advanced Linux Sound Architecture)…

  • …full audio and MIDI functionality for Linux
  • Kernel sound card drivers since Linux 2.6 (1998)
  • User space driven library for application developers
  • Optional OSS emulation mode for /dev/sound, /dev/dsp, etc
  • Device files in /dev/snd/ (use alsa-lib instead)
# kernel messages for sound devices
sudo dmesg | egrep -i "alsa|snd"  
# verify that sound modules are loaded
lsmod | grep '^snd' | column -t

Configuration

/proc/asound kernel interface

/proc/asound/version              # ALSA version
/proc/asound/cards                # list of registered cards
# PCM device-related information and status
tail -n+2 /proc/asound/card[0-9]/pcm*/info
# list of registered ALSA devices
>>> cat /proc/asound/devices
  2: [ 0- 0]: digital audio playback
  3: [ 0- 0]: digital audio capture
  4: [ 0- 3]: digital audio playback
  5: [ 0- 7]: digital audio playback
  6: [ 0- 8]: digital audio playback
  7: [ 0- 9]: digital audio playback
  8: [ 0-10]: digital audio playback
  9: [ 0- 0]: hardware dependent
 10: [ 0- 2]: hardware dependent
 11: [ 0]   : control
 33:        : timer
  |    |  |
  |    |  `- device number
  |    `---- card number
  `--------- minor number

ALSA library configuration:

/usr/share/alsa/alsa.conf
/etc/asound.conf
~/.asoundrc

Save settings (volume states) for device:

alsactl store      # store alsamixer confguration
alsactl restore    # restores the saved alsamixer state

alsamixer & aplay

Users have permission to play audio and change mixer levels:

amixer                            # configure audio settings
alsamixer                         # ..using a TUI
# list audio devices
aplay -l
aplay -L | grep :CARD
# produce noise on a device
speaker-test -D default:PCH -c 2

Keyboard volume control:

amixer set Master 5%+      # increase volume
amixer set Master 5%-      # decrease volume
amixer set Master toggle   # toggle mute

pulseaudio

pulseaudio -vvvvv                # start in foreground with debugging
pulseaudio -k                    # kill running server
pulseaudio -D                    # start as daemon
pacmd ls                         # show audio system state
pulsemixer                       # curses base volume control/mixer
pavucontrol                      # GTK based volume control/mixer
# input sources (* indicates current default)
pacmd list-sources | grep -e 'index:' -e device.string -e 'name:'
# output sources
pacmd list-sinks | grep -e 'name:' -e 'index:'

PulseAudio under the hood (2017)
https://gavv.github.io/articles/pulseaudio-under-the-hood

Music

SoX

SoX…

  • …Swiss Army knife of sound processing programs
  • …Fedora sox package
  • …documentation
  • …includes play command
# play a list of MP3 files...
play path/to/*.mp3

mpd

MPD (music player daemon)…

Configuration…

  • …$SCRIPTS/etc/mpdconf (in my case)
    • …$HOME/music stores all music files…
    • …$HOME/.mpd stores all run-time information
  • …configuration is stored a version control system
bind_to_address         "127.0.0.1"
port                    "12345"
music_directory         "~/music/"
auto_update             "yes"
playlist_directory      "~/.mpd/playlists"
db_file                 "~/.mpd/mpd.db"
log_file                "~/.mpd/mpd.log"
pid_file                "~/.mpd/mpd.pid"
volume_normalization    "yes"

#audio_output { 
#  type                  "alsa"
#  name                  "My ALSA Device"
#}

audio_output {
        type            "pulse"
        name            "pulse audio"
        mixer_type      "hardware"
}

Some shell-init …$SCRIPTS/var/aliases/mpd.sh (in my case)…

  • …starts mpd using custom configuration (above)
    • …unless running already
    • …requires exigences of $HOME/music
command -v mpd >/dev/null && {

        MPD_CONF=$SCRIPTS/etc/mpdconf
        # read the port from the configuration file
        MPD_PORT=$(grep ^port $MPD_CONF | cut -d'"' -f2)
        MPD_PLAYLISTS=$HOME/.mpd/playlists
        MUSIC_DIR=$HOME/music
        
        export MPD_PORT \
               MPD_CONF \
               MPD_PLAYLISTS \
               MUSIC_DIR

        if [ -d $MUSIC_DIR ]
        then
                # if MPD is not running
                if ! pgrep -u $USER mpd &>/dev/null
                then
                        [[ -d $MPD_PLAYLISTS ]] || mkdir -p $MPD_PLAYLISTS
                        # start MPD
                        mpd $MPD_CONF 2>&-
                        # update music index
                        mpc -w update
                        echo mpd started
                fi
        fi

}

mpc & ncmpc connecting to the MPD instance…

alias mpc="mpc --host 127.0.0.1 -p $MPD_PORT"
alias ncmpc="ncmpc --host 127.0.0.1 --port $MPD_PORT"

Pictures

Editor

gThumb 1 is a basic image browser with editing…

  • …thumbnail browser & image viewer for all common formats
  • …editor …coloring, scale, crop, etc.
  • …basic image conversion & slide-shows

Screenshot

Screenshots…

  • …capture entire screen
  • …a particular application window
  • …any user defined area

GNOME includes a simple screenshot tool…

  • …press print key for accecss …esc to exit
    • s …select area
    • c …capture screen
    • w …capture window
    • t …toggle mouse pointer
  • …annotation with GNOME Drawing

Alternatively …Flameshot screenshot application…

  • …command-line interface
  • …more options …more complex user GUI
  • …includes annotation tools
  • Install…