This program consists of a client and a server component allowing synchronous audio playback over the network. This Software is heavily inspired by snapcast. The server obtains its input from a fifo which is fed by any audio player (or even converter) that supports playing to this fifo. The server can be controlled by the existing android app.
This Implementation focuses on a small maintainable single-threaded design while aiming for good audio quality. After all, music is meant to be enjoyed. The code currently relies on poll/epoll/timefd/alsa and thus is specific to Linux. Patches for other platforms are welcome.
- Latency is induced by snapcast to compensate short network outages.
- The design of snapcast (reading from an input pipe) induces significant latency. Pipes in Linux by default buffer up to 64KB of data. On my machine I can see that once in a while the input pipe will not be read for multiple seconds. To compensate I am running snapcast with a very large buffer.
- That being said, care has been taken to allow immediate playback and pausing when using elastic pipes.
While it is important for clients to run on small devices, audio quality is valued above CPU utilization. The smallest target platform is Raspberry PI B.
On this device which is clocked to 800Mhz, when using Opus, snapcastc-client utilizes 14% CPU. snapcastc-server utilizes 36% CPU during regular playback for a single stream. When starting a stream the buffers are filled and snapcastc-server will max out a single core.
This means there a single Pi can run snapcastc-server, snapcastc-client and there is barely enough room for mpd - but nothing more. Once the buffers are filled, the pi runs with 85-90%% CPU usage
Once available, stable packages will be pushed to the OSS packagecloud repository:
curl -s https://packagecloud.io/install/repositories/christf/OSS/script.deb.sh | sudo bash
Until that time, you are welcome to use the development packages for debian and raspbian from packagecloud.
curl -s https://packagecloud.io/install/repositories/christf/dev/script.deb.sh | sudo bash
See roadmap for implementation status.
MPD has two output plugins that can potentially be used: pipe and fifo. The fifo plugin will never block mpd at the expense of dropping audio data when the fifo is full. This is 64KB on a Linux > 2.6.11 When the server is under significant IO load, this will lead to dropped audio.
The pipe plugin makes the choice the other way around: It will not drop audio data but it will block playback in mpd when data cannot be processed. As long as blocking does not take longer than the configured buffer of snapcast, it will not be audible.
If you are using the fifo output plugin from mpd and playback stops on all clients simultaneously after they have been playing for more than 30 minutes, then consider switching to the following mpd configuration in mpd.conf. Also, make sure that the snapfifo is created using mkfifo and snapcastc as well as mpd have permission to access it.
audio_output {
type "pipe"
name "snapcast"
command "cat >/tmp/snapfifo"
format "48000:16:2"
auto_resample "no"
}
Allowed options:
-h, --help Produce help message
-V, --version Show version number
-v verbose output
-d debug output
-p <port> Server UDP port (default: 1704)
-P <port> Remote TCP control port (default: 1705)
-s <file> filename of the PCM input stream.
-c, --codec arg (=opus) Default transport codec *
(flac*|opus|pcm*)[:options]
-b, --buffer arg (=1000) Read ahead buffer before playing [ms]
Options marked with (*) are not implemented yet.
I am starting snapserver like this:
snapcast-server -b 25000 -s "pipe:///tmp/snapfifo?buffer_ms=120&codec=opus&name=default&sampleformat=48000:16:2" -p 1704
Allowed options:
-h --help produce help message
-V, --version show version number
-v verbose output
-d debug output
-l list pcm devices
-m <control> name of the mixer device
-c <card> sound device on which the mixer lives eg "hw:1"
-s <playback_device> index or name of the soundcard
-H, --host arg server hostname or ip address
-p (=1704) server port
-L arg (=0) latency of the client in ms
-i, --instance arg (=1) instance id
I am starting the client like this:
snapcast-client -H <hostname-of-server> -p <port of server - 1704> -s default
Alsa allows to create custom volume controls. This can be achieved by editing /etc/asound.conf
Pcm.snapclient {
Type softvol
Slave.pcm "asymed"
Control.name "snapclient"
Control.card 1
}
to use this control, use the parameters:
-m snapclient
-c hw:1
-s snapclient
The scripts directory contains a set of example api calls to mute/unmute clients, set their volume and move clients to different streams to illustrate API usage and provide scripts to be integrated into your home automation.
For testing, the following commands can be executed to generate some audio
mkfifo /tmp/snapfifo
sox input.ogg -r 48000 -t raw -b 16 -e signed -c 2 /tmp/snapfifo
In a different terminal, start
./src/snapcast-server -s "pipe:///tmp/snapfifo?name=default&codec=opus&sampleformat=48000:16:2&buffer_ms=120" -b 30000 -p 1704 -v
And yet in another terminal, start
./build/src/snapcast-client -H localhost
- Audio Playback [Working]
- Usage of UDP for transporting media data [Working]
- Support for Opus [Working]
- Synchronous playback by dropping / inserting single frames [Working]
- Synchronous playback by time stretching audio chunks using libsoxr [Working]
- Synchronous playback by time stretching audio chunks using librubberband while maintaining pitch [patches welcome]
- Support for Snapcast andoid app [patches welcome]
- implement missing command line options [patches welcome]
- The Audio player will have to resample to a fixed sample rate.
- exclusively Linux is supported (patches welcome)
The included Dockerfile provides a build environment, that is used for the travis-ci integration. See the script section of .travis.yml on how to run it. Of course, this can be used to build SnapCastC on your own infrastructure.
apt install libasound2 libopus libsoxr0 libjson-c3 librubberband2
apt install cmake libsoxr-dev librubberband-dev libasound2-dev libopus-dev build-essential git libjson-c-dev
in the root of this project, run:
mkdir build
cd build
cmake ..
make -j5
make install
to build and install the program.
- clients say hello to servers
- servers maintain a list of clients that have recently said hello
- when playing data, it is sent to each client using unicast UDP
- every data packet has a sequence number
- when a client receives a sequence number n+1 but has not received m it will REQUEST missing packets from the server
To integrate SnapCastC with fhem mute button and volume sliders can be defined: The two snapcast clients are started using -i 2 and -i 3 respectively to hard-code their ID.
define Musik_Wohnzimmer dummy
Attr Musik_Wohnzimmer devStateIcon on:audio_volume_high off:audio_volume_mute .on:audio_volume_high
Attr Musik_Wohnzimmer icon audio_volume
Attr Musik_Wohnzimmer room Musik
Attr Musik_Wohnzimmer setList on off
Define off_Musik_Wohnzimmer notify Musik_Wohnzimmer:off {system("snapclient_mute 3 true")}
Define on_Musik_Wohnzimmer notify Musik_Wohnzimmer:on {system("snapclient_mute 3 false")}
Define Musik_Kueche dummy
Attr Musik_Kueche devStateIcon on:audio_volume_high off:audio_volume_mute
Attr Musik_Kueche room Musik
Attr Musik_Kueche setList on off
Define off_Musik_Kueche notify Musik_Kueche:off {system("snapclient_mute 2 true")}
Define on_Musik_Kueche notify Musik_Kueche:on {system("snapclient_mute 2 false")}
Define Lautstaerke_Kueche dummy
Attr Lautstaerke_Kueche icon audio_audio
Attr Lautstaerke_Kueche readingList state
Attr Lautstaerke_Kueche room Musik
Attr Lautstaerke_Kueche setList state:slider,0,2,100
Attr Lautstaerke_Kueche webCmd state
Define n_Lautstaerke_Kueche notify Lautstaerke_Kueche {system("/usr/local/bin/snapclient_setvolume 2 $EVENT")}
Define Lautstaerke_Wohnzimmer dummy
Attr Lautstaerke_Wohnzimmer icon audio_audio
Attr Lautstaerke_Wohnzimmer readingList state
Attr Lautstaerke_Wohnzimmer room Musik
Attr Lautstaerke_Wohnzimmer setList state:slider,0,2,100
Attr Lautstaerke_Wohnzimmer webCmd state
Define n_Lautstaerke_Wohnzimmer notify Lautstaerke_Wohnzimmer {system("/usr/local/bin/snapclient_setvolume 3 $EVENT")}
Help is much appreciated. Be it testing and opening specific issues, or contributing code or ideas - every improvement is welcome. Sometimes there are different ideals for structuring changes. Please work with us to keep the project maintainable.
If you can improve this project (typos, better wording, restructering, ...) or even new important aspects, feel free to open a pull request. Please consider the Seven Rules when writing commit messages.
This approach makes reviewing and reasoning about changes a lot easier.
Some of us are in #snapcastc on freenode.
This project is inspired by snapcast. Its concept of playback from a pipe and the android App are re-used for snapcastc. Thank you, badaix for this inspiration and the proof that this can be achieved!