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BlitzLoop on a Raspberry Pi

BlitzLoop can be installed on a Raspberry Pi, for what might possibly be the world's smallest and cheapest full-featured karaoke box.

Normally, BlitzLoop runs on OpenGL on GLX on Xorg, and uses mpv with the opengl-cb backend. The Raspberry Pi does not work efficiently with this setup. However, BlitzLoop also supports a native Raspberry Pi backend, which uses EGL directly without Xorg, and takes advantage of the hardware compositor to display karaoke lyrics on a layer above the video playback layer, provided by mpv's rpi backend. This guide focuses on this specific Raspberry Pi support.

Prerequisites

  • Raspberry Pi 3
  • Arch Linux ARM

BlitzLoop has only been tested on a Raspberry Pi 3. Previous models may not be powerful enough to work properly. Feel free to try.

Installation

Base OS

Follow the Arch Linux ARM installation guide for Raspberry Pi 3 (32bit version).

It is assumed that you are using the default alarm user to run BlitzLoop. Additionally, you might want to change the password for alarm and/or root, set up SSH keys, etc.

Make sure your Ethernet network is properly configured and you have internet access (Arch Linux ARM uses DHCP by default), at least during installation. We will be using WiFi as an AP for the client remote control devices to connect to; it is possible to configure WiFi as a client to an existing network, but that is beyond the scope of this guide.

This guide assumes that you have sudo installed and configured. If you don't, run the commands prefixed with sudo as root (e.g. su).

Set boot options

cat <<EOF | sudo tee /boot/config.txt > /dev/null
gpu_mem=256
disable_overscan=1
dtparam=audio=on
EOF

Also set the CPU frequency scaling policy to performance (otherwise rendering FPS will randomly vary):

cat <<EOF | sudo tee /etc/tmpfiles.d/10-fast-cpu.conf
w /sys/devices/system/cpu/cpufreq/policy0/scaling_governor - - - - performance
EOF

Reboot.

Configure environment

Set the locale to something with UTF-8:

echo 'en_US.UTF-8 UTF-8' | sudo tee /etc/locale.gen
sudo locale-gen
echo 'LANG=en_US.UTF-8' | sudo tee /etc/locale.conf

Grant alarm audio access and real-time priority for JACK:

sudo usermod -aG audio alarm
echo 'alarm - rtprio 99' | sudo tee -a /etc/security/limits.conf

Log out and back in.

Update system

sudo pacman -Syu

Install dependencies and BlitzLoop

We need a bunch of dependencies from AUR, which will be a lot easier to do with yaourt:

# Manually pull in jack2 instead of jack, which works better here
sudo pacman -S --needed base-devel jack2 alsa-tools alsa-utils wget git

mkdir -p ~/pkg; cd ~/pkg
wget https://aur.archlinux.org/cgit/aur.git/snapshot/package-query.tar.gz
tar xvzf package-query.tar.gz
cd ~/pkg/package-query
MAKEFLAGS="-j4" makepkg --skippgpcheck --syncdeps
sudo pacman -U package-query-*.pkg.tar.xz

cd ~/pkg
wget https://aur.archlinux.org/cgit/aur.git/snapshot/yaourt.tar.gz
tar xvzf yaourt.tar.gz
cd ~/pkg/yaourt
MAKEFLAGS="-j4" makepkg --skippgpcheck --syncdeps
sudo pacman -U yaourt-*.pkg.tar.xz

cd ~/pkg
yaourt -S mpv-rpi
yaourt -S blitzloop-git

Configure BlitzLoop

mkdir -p ~/.config/blitzloop
cat <<EOF >~/.config/blitzloop/blitzloop.conf
display=rpi
mpv-vo=rpi
EOF

Get songs

Put your songs in /home/alarm/.local/share/blitzloop/songs/ (create it first).

Test out BlitzLoop

Run:

cd ~
blitzloop --mpv-ao=alsa --no-audioengine

Connect to TCP port 10111 and check to see if everything works properly. Note that you will not have any microphone support at this point, as the Raspberry Pi has no audio input.

If you have no audio, you may need to run amixer cset numid=3 2.

Systemd service

cat >~/startblitz.sh <<EOF
#!/bin/sh
cd "\$(dirname "\$0")"
amixer cset numid=3 2
python -u /usr/bin/blitzloop --port=80 --no-audioengine --mpv-ao=alsa
EOF
chmod +x ~/startblitz.sh

cat <<EOF | sudo tee /etc/systemd/system/blitzloop.service > /dev/null
[Unit]
Description=BlitzLoop

[Service]
Type=simple
User=alarm
Group=alarm
ExecStart=/home/alarm/startblitz.sh
KillMode=mixed
TimeoutStopSec=5
AmbientCapabilities=CAP_NET_BIND_SERVICE
LimitRTPRIO=99
LimitMEMLOCK=1024000000

[Install]
WantedBy=multi-user.target
EOF

sudo systemctl enable blitzloop
sudo systemctl start blitzloop

Mic setup

To get microphones supported, you will need to configure JACK. If you have a single USB sound card you want to use for input/output, do something like this in ~/startblitz.sh:

#!/bin/sh
cd "$(dirname "$0")"
export JACK_NO_AUDIO_RESERVATION=1
jackd -R --timeout 10000 -d alsa -D hw:AUDIO -r 48000 -p 240 -n 2 -o 2 &
jack_pid=$!
trap "kill $jack_pid" EXIT
sleep 1
python -u /usr/bin/blitzloop --port=80 --mpv-ao=jack --mics=system:capture_1,system:capture_2

Where hw:1 is your desired audio device (you can look in /proc/asound/cards for symbolic names you can use instead of index numbers which may change, and use them as e.g. hw:AUDIO).

If you have separate cards for input/output (e.g. you want to use built-in or HDMI audio for output, or have a separate USB microphone and sound card), try something like this:

#!/bin/sh
cd "$(dirname "$0")"
export JACK_NO_AUDIO_RESERVATION=1
jackd -R --timeout 10000 -d alsa -P hw:AUDIO -r 48000 -p 240 -n 2 -o 2 &
jack_pid=$!
alsa_in -j mic -d hw:Receiver -c 2 -p 240 -n 2 -q 0 &
alsa_pid=$!
trap "kill $jack_pid $alsa_pid" EXIT
sleep 2
python -u /usr/bin/blitzloop --port=80 --mpv-ao=jack --mics=mic:capture_1,mic:capture_2 "$@"

WiFi setup

Set up a WiFi hotspot for tablets to connect to:

sudo pacman -S --needed dnsmasq hostapd iptables

cat <<EOF | sudo tee /etc/hostapd/hostapd.conf >/dev/null
interface=wlan0
ssid=BlitzLoop
hw_mode=g
channel=6
wmm_enabled=1
EOF
sudo systemctl enable hostapd
sudo systemctl start hostapd

cat <<EOF | sudo tee /etc/dnsmasq.conf >/dev/null
no-resolv
server=8.8.8.8
address=/blitz/192.168.42.1
address=/bl/192.168.42.1
address=/b/192.168.42.1
interface=wlan0
dhcp-range=192.168.42.100,192.168.42.200,12h
EOF

sudo systemctl enable dnsmasq
sudo systemctl start dnsmasq

cat <<EOF | sudo tee /etc/systemd/network/hostap.network >/dev/null
[Match]
Name=wlan0

[Network]
Address=192.168.42.1/24
IPMasquerade=yes
EOF

sudo systemctl restart systemd-networkd.service

Now you can connect to the BlitzLoop SSID and browse to http://b/.

Limitations / known bugs

Audio processing already uses most of one core by default. Changing the speed or tempo in certain ways causes increased CPU usage and drop-outs.