Audio Teleport

Simple client/server for sending audio from one (Linux) host to another.

Setup

Installation

1. Clone this repo
2. Run build.sh to create rpm and deb packages
3. Install package on client and server
4. Edit /etc/audio-teleport on the client and set the server details
5. Run audio-teleport on the client

Configuration

• /etc/audio-teleport is created by the package
• ~/.config/audio-teleport is created the first time you launch audio-teleport
• /etc/systemd/system/audio-teleport-listener@.service contains a User ID that you may need to change (if your UID!=1000)

How does it work?

Client side

Creates a dummy Pulseaudio playback device (sink) and sets it as default. It then records audio, compresses it and streams it to the server.

Server side

Uses systemd socket activation to detect incoming audio and start a service to buffer it and play it.

Why?

After trying various methods to stream audio to a Raspberry Pi connected to my home audio, I found a combination that worked consistently for me. My requirements, in order of importance, were:

1. Consistency: zero gaps, skips, pops, clicks
2. Quality: zero loss of fidelity
3. Latency: as close to zero latency as possible, without compromising #1 or #2

Results

• Consistency is 100% so far
• Quality is perfect (lossless compression)
• Latency is "OK" (ranges from 1-6 seconds)

TODO

1. Create a simple GUI to start/stop the client, configure it etc
2. Application shortcut (.desktop) to launch the GUI
3. Implement a kludgey 'watcher' that automatically stops the client after 5 minutes of silence
   • record 1s low-quality sample, test it for silence using ffmpeg
   • if it detects silence, increment counter, else reset to 0
   • if counter reaches X, stop the client
4. Figure out the best way to run the capture with higher priority (rt if possible)

Nitty gritty

Recording

If you're using PipeWire or Pulseaudio, this should work. You just need to make sure you have the Pulseaudio utils pactl (to create the null sink) and parec (to record audio)

Compression

This project uses lossless flac compression. Not only is is lossless, but it's the fastest compression I've found. I compared it against the excellent Opus codec, but it added a noticeable delay (several seconds!).

Send

Good old netcat!

Socket listener

On the server side, it uses Systemd socket activation to detect traffic on port 12345. Once audio arrives, Systemd launches a service to play it.

Buffering / playback

The service that plays audio first buffers it using mbuffer. This, in my experience, is the main factor in making the music reliable. Before I added it, I had major issues with reliablilty. There are several options that can be tuned, and I'll make these available through /etc/audio-teleport at some point. But right now, it works fine for me!