Install McLaren Labs’ rtpmidi on Chromebook Linux Bookworm

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Our port of rtpmidi to Debian 12 (Bookworm) installs effortlessly in the Chromebook Linux subsystem. Why would you want to do this? The reason is to get MIDI events from external devices into the Linux subsystem of your Chromebook.

McLaren Lab’s rtpmidi installed in Chromebook LInux

Currently, when you plug a MIDI device into the USB of your Chromebook, it is not passed through to the Linux subsystem. By using rtpmidi you can send MIDI events from a device connected to another computer into the Linux subsystem of your Chromebook.

When used with a wired Ethernet connection (avoiding WiFi) the latency of such a set-up can rival a direct connection.

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LXD/rtpmidi – running McLaren Labs rtpmidi in a container

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Container technology can be used for many things. It can be used for isolation, security, portability or resource management. One popular use of containers is to run a binary for one operating system on another operating system. We wondered if Linux lxc/lxd container technology would allow us to run the binary of rtpmidi for Ubuntu 22.04 on a Debian 12 system. We succeeded eventually.

This post outlines how we reached success. It is not necessarily a recommendation to follow this path. There are a lot of steps, and they can be confusing. But we are going to write down what we learned anyway.

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Chromebook, Crostini Linux and MIDI

A few weeks ago I picked up an inexpensive Chromebook. I’m typing this on it now, in fact. This was my first experience with Chromebook, and my first experience thinking about porting McLaren Labs’ tools onto a Chromebook. At first, I was thinking about wiping ChromeOS and putting Debian11 directly on it. But then I learned about native Linux support on Chrome in a VM.

Chromebook Linux

Crostini is the name given to the Linux-on-Chromebook virtual machine support. To enable it on my chromebook, I needed to open chrome://flags and enable Linux. Then I rebooted, and in Settings>>Advanced there was a new section called “Linux”. Voila.

Applications that need the Linux environment cause the Linux VM to start. One application is “Terminal” in the main applications menu. Start it up, and there is a full Debian 11 environment there. You can use “apt-get” and install whatever you desire.

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Announcing McLaren MIDI Kit – RTP-MIDI library for your own projects

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The McLaren Synth Kit — https://github.com/mclarenlabs/McLarenSynthKit — now includes an RTP-MIDI engine that you can include in your own projects. The engine is the same one that is in our well-known rtpmidi product! We’re providing the library so that you can set up RTP-MIDI connections as you like.


We sometimes receive requests from users to add features to McLaren Labs’ rtpmidi product to handle connections in a certain way. Some users might want to automatically find a particular endpoint or address. Another user might want automatic re-connect in a certain situation. Others want to experiment by translating events from non-MIDI sources into note events sent to a synthesizer on their network.

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Arduino AppleMIDI and McLaren rtpmidi

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SparkFun ESP2866 “Thing Dev” board

One of our customers brought to our attention an implementation of RTP MIDI for Arduino. With this sketch, you can use an Arduino to send and receive MIDI over Ethernet and WiFi. It is compatible with McLaren Labs’ rtpmidi, so you can use it to send MIDI from an Arduino to your Raspberry Pi.

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Enabling memlock for rtpmidi on Ubuntu 20.10

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In version 0.5.2 of McLaren Labs’ rtpmidi, we made the use of locked memory the default. Locked memory dedicates fixed RAM to the rtpmidi process, and prevents it from being swapped to disk. The use of locked memory (through the mlockall() function call) can be a benefit to realtime applications like MIDI and Audio, but its use can be to the detriment of other processes. So it should be used carefully.

On Ubuntu 18.04 and 20.04 enabling memlock as the default option seemed benign enough. On Ubuntu 20.10, however, this default caused problems. With memlock enabled, the process printed strange errors and aborted. Example:

***MEMORY-ERROR***: rtpmidi[2023]: GSlice: failed to allocate 8176 bytes (alignment: 8192): Cannot allocate memory

Ubuntu 20.10 (Groovy Gorilla) accounts for locked memory pages differently, and even though the memory limit is higher, with all things accounted for, it is not enough.

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Use the ‘favorite’ Option to Automatically Initiate a MIDI Session

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When you use our rtpmidi tool to connect two devices you have created a “session.” The session has an “initiator” side that started the connection, and “listener” side that accepted the invitation. Some devices, however, do not make good “initiators” and iPhones are a great example. An iPhone cannot initiate a network MIDI session.

But sometimes you want an iPhone to join the MIDI network of a stationary computer … without going back to the computer screen. McLaren Labs’ “favorite” option was created to handle this case.

A “favorite” is the name of a device that that rtpmidi automatically initiates a session with whenever the favorite appears on the network. This new feature takes advantage of the properties of Bonjour (Avahi). A Listener advertises its availability using Bonjour. When rtpmidi detects a Bonjour name matching a favorite, it automatically initiates a session with that name.

Use the “favorite” option from the command line like this.

$ rtpmidi gui -F 'myiPhone' -t Organ-Synth:0

Now, whenever rtpmidi sees the iPhone named “myiPhone” it will automatically call it and route MIDI information to “Organ-Synth”.

A Demonstration

The video below shows how this works.

Using the ‘favorite’ option to automatically connect
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