libremidi

libremidi is a cross-platform C++20 library for real-time and MIDI file input and output.

This is a fork / rewrite based on two libraries:

• RtMidi
• ModernMIDI

Additionnally, for MIDI 2 parsing support we use cmidi2!

Read the documentation here.

Citation

If you use this work as part of academic research, please kindly cite the paper:

@inproceedings{celerier2024libremidi,
  title={libremidi: a cross-platform library for real-time MIDI 1 and 2},
  author={Celerier, Jean-Micha{\"e}l},
  booktitle={Proceedings of the Sound and Music Computing Conference (SMC)},
  year={2024},
  address={Porto, Portugal}
}

Changelog

Since v5

• Use stdx::error for error reporting until C++26 and std::error are widely available :-)
• Hunt exceptions down
• Basic I/O & observer with the Windows MIDI Services.
  • Using Developer Preview 5, currently the most recent: https://github.com/microsoft/MIDI/releases/tag/dev-preview-5
• C API for bindings to other languages (libremidi-c.h).
• Python binding.
• Support for getting raw, unfiltered MIDI data (e.g. no SYSEX recombination logic).
• Computer Keyboard backend to easily map scancodes to keyboard-like MIDI maps ⌨.
• Network backend to send MIDI 1 and UMP packets over OSC 🛜.
• libremidi finally supports MIDI 2 on all desktop platforms 🎉!

Since v4.5

• Input logic refactored across all backends.
  • e.g. previously not backends had the same rules wrt timestamping, sysexes, etc. Now there is a single MIDI state machine which processes this.
• PipeWire support.
• Many bugfixes across the stack.

Since v4.4

• iOS support restored (thanks @fwcd)
• CI work: added Debian Bullseye, Bookworm, Trixie and make sure UMP code is being built.
• Add compatibility with ni-midi2: the libremidi::ump type will convert automatically from / to midi::universal_packet and it is possible to send directly some ni-midi2 data types through libremidi::midi_out.
• Added an example of very basic MIDI-CI interoperation with MIDI2.0Workbench: https://github.com/jcelerier/libremidi/blob/master/examples/midi2_interop.cpp
• Observer: add a track_any flag to track MIDI ports that are not reported as being hardware or software.
• UMP: allow send_ump to handle UMP streams, not only single UMP packets.

Since v4.3

• Improvements to timing handling.
  • Added a Custom timestamping mechanism which allows the user to provide a custom callback to run timestamping as close as possible to the event's reception.
  • Added midi_in::absolute_timestamp() to get the origin timestamp for driver-provided ticks as accurately as possible.
  • e.g. in practice this is taking the time just near the ALSA queue creation or WinMM MIDI open.
  • Bugfixes in JACK
  • Many warning fixes - thanks @lilggamegenius for the extensive work!
  • Fix MIDI dump example - thanks @chdiesch!
  • Add SOVERSION to dynamic library

Since v4.2

• More robust MIDI 2.0 support.
  • On macOS through CoreMIDI (input / output, requires macOS 11+).
  • On Linux through ALSA sequencer API (input / output, requires kernel 6.5+ and latest libasound).
  • The API can be used through MIDI 1 or MIDI 2 affordances, e. g. one can send UMP packets to a MIDI 1 API, they will get converted automatically.
  • More backends to come, in particular with the new Windows MIDI Services started here!
  • Sysex handling on MIDI 2.0 is the responsibility of the user of the library, which simplifies the design immensely and allows the library to be used in stricter real-time contexts (as an UMP message has a fixed size, unlike MIDI 1 sysex which required potentially unbounded dynamic allocations with the previous design).
  • See midi_echo.cpp for a complete example.
• Linux: libasound and udev are now entirely loaded at run-time through dlopen. This is necessary for making apps that will run on older Linux versions which do not have the ALSA UMP APIs yet. Note that to make an app which supports MIDI 2 on recent Linuxes and still runs on older ones, you will need to use the latest ALSA library headers as part of your build on an older distribution, by building alsa-lib yourself (as the old distributions with an old glibc that you want to build against to make compatible software of course also ship an old libasound which won't have the UMP API...).

Since v4

• Experimental MIDI 2.0 support.
• A neat configuration system which enables to pass options to the underlying backends.
• Possibility to share the contexts across inputs and outputs to avoid creating multiple clients in e.g. JACK.
• Hotplug support for all the backends!
• Reworked port opening API which now uses handles instead of port indices to increase robustness in the face of disconnection / reconnection of MIDI devices.
• Integer timestamps everywhere, and in nanoseconds. Additionnally, it is now possible to choose different timestamping methods (e.g. relative, absolute monotonic clock...).
• Experimental API to allow to poll manually in ALSA (Sequencer and Raw), in order to give more control to the user and enable processing events on any kind of Linux event-loop.
• Increase the checks done by the MIDI parser.
• Internally it's pretty much a complete rewrite. Standard threading primitives are now used, as well as modern Linux facilities for polling control (eventfd, timerfd). Most of the code has been refactored.
• Ability to set a fixed message size for zero-allocation scenarios, with -DLIBREMIDI_SLIM_MESSAGE=<NBytes> (in CMake or directly to the compiler)

Since v3

• Allow to pass span when available (C++20) or (uint8_t* bytes, std::size_t size) pairs whenever possible to reduce copying.

Since v1

• The library can be used header-only, as explained in the docs
• Callbacks are passed by std::function and generally simplified.
• Ability to use boost::small_vector to pass midi bytes instead of std::vector to reduce allocations.
• Less indirections, virtuals and memory allocations.
• Simplify usage of some functions, use C++ return style everywhere.
• Use of standard C++ snake_case.
• Simplification of exceptions.
• Passes clean through clang-tidy, clang analyzer, GCC -Wall -Wextra, ASAN, UBSAN etc etc.
• Support chunking of output data (only supported on raw ALSA backend so far).

New & improved backends

• JACK support on Windows.
• JACK support through weakjack to allow runtime loading of JACK.
• UWP MIDI support on Windows
• Emscripten support to run on a web browser with WebMIDI.
• Raw ALSA support in addition to the existing ALSA sequencer support.

Roadmap

• Migrate to std::expected instead of exceptions for error handling.
• Finish MIDI 2 implementations, provide helpers, etc.
• ~More tests and compliance checks~
• ~Work even more towards this library being a zero-cost abstraction on top of native MIDI APIs~
• ~Rethink some design issues with the original RtMidi, for instance the way port numbers work is not reliable~
• ~Refactor duplicated code across backends~

They use this library

• BlastThruReborn
• BraneEngineDx
• chordcat
• EraeTouchLite
• MIDIVisualizer
• ossia.io
• obs-midi-mg
• SceneSwitcher
• Senos
• SynthMania
• zing