mtrx

Transmit and receive audio via UDP unicast or multicast, using the Opus codec.

Copyright (C) 2014-2017 Vittorio Gambaletta

mtx

Usage: mtx [<options>]

    -h <addr>   IP address (default: 239.48.48.1)
    -p <port>   UDP port (default: 1350)
    -d <dev>    ALSA device name, or '-' for stdin (default: 'default')
    -R <n>      RTP output (default: 0)
    -f <n>      Use float samples (1) or signed 16 bit integer samples (0) (default: 0)
    -r <rate>   Audio sample rate (default: 48000 Hz)
    -c <n>      Audio channel count (default: 2)
    -t <ms>     Audio packet duration (default: 20 ms)
    -k <kbps>   Network bitrate (default: 128 kbps)
    -b <n>      ALSA buffer multiplier (default: 3)
    -T <n>      Enable or disable time synchronization (default: 1)
    -v <n>      Be verbose (default: 0)

mrx

Usage: mrx [<options>]

    -h <addr>   IP address (default: 239.48.48.1)
    -p <port>   UDP port (default: 1350)
    -d <dev>    ALSA device name, or '-' for stdin/stdout (default: 'default')
    -f <n>      Use float samples (1) or signed 16 bit integer samples (0) (default: 0)
    -r <rate>   Audio sample rate (default: 48000 Hz)
    -c <n>      Channels count (default: 2)
    -t <ms>     Audio packet duration (default: 20 ms)
    -b <n>      ALSA buffer multiplier (default: 3)
    -e <ms>     Audio total delay (default: 80 ms)
    -T <n>      Enable or disable time synchronization (default: 1)
    -v <n>      Be verbose (default: 0)

Quick 'n' easy steps to transmit audio routed from PulseAudio

• First clone the repo and run make ;)

Transmitter

First time

• Append this to /etc/asound.conf:

pcm.pnm {
	type pulse
	device null.monitor
}

Every time

• Run pacmd load-module module-null-sink (once per session)
• Run sudo ./mtx -d pnm -f 1 (the root privs are needed to get realtime priority)
• Change network bandwidth with -k if needed
• Run pavucontrol and move streams that need to be streamed to the Null Output sink
• Run pacmd unload-module module-null-sink at the end if you want

Receiver(s)

• Run sudo ./mrx (the root privs are needed to get realtime priority)
• Change receiving latency with -e if needed
• If having problems try sudo ./mrx -d pulse
• On OpenWrt and/or with cheap USB audio cards without PulseAudio, if it doesn't work try mrx -d plughw:0,0
• It shouldn't be needed anymore, but it might still be useful, so this is a working /etc/asound.conf file for OpenWrt with cheap USB audio cards

RTP

RTP output is useful for transmitting to other applications, e.g. FFmpeg. You don't need any PulseAudio integration; just run mtx with -R 1 and -d etc. as usual. This will output an SDP file, which you can run in e.g. ffplay with

ffplay -protocol_whitelist rtp,file,udp -i mtx.sdp

Bugs

• Well, all the desync bugs seem to happen (and needed a resync hack in mtx) only when using alsa-pulse to capture from the null output sink monitor...
• If you find any bugs, please report them! :)

TODO

• Support IPv6
• Implement native PulseAudio interface (but only if it doesn't bloat the program! The target is embedded systems like OpenWrt routers...)
• OpenWrt/LEDE packaging
• On OpenWrt, libopus is compiled with floating point enabled by default, and since floating point is emulated on most routers' CPUs, it's SLOW as hell. Maybe send a patch to LEDE (if that was not already done in the meantime)?
• Any suggestion?

License

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.