RTP-MIDI (also known as AppleMIDI) is a protocol to transport MIDI messages within Real-time Transport Protocol (RTP) packets over Ethernet and WiFi networks. It is completely open and free (no license is needed), and is compatible both with LAN and WAN application fields. Compared to MIDI 1.0, RTP-MIDI includes new features like session management, device synchronization and detection of lost packets, with automatic regeneration of lost data. RTP-MIDI is compatible with real-time applications, and supports sample-accurate synchronization for each MIDI message.
History of RTP-MIDI In 2004, John Lazzaro and John Wawrzynek, from UC Berkeley, made a presentation in front of AES named "An RTP payload for MIDI".An RTP Payload format for MIDI. The 117th Convention of the Audio Engineering Society, October 28-31, 2004, San Francisco, CA. In 2006, the document was submitted to IETF and received the number RFC 4695.RTP Payload format for MIDI - RFC 4695 In parallel, another document was released by Lazzaro and Wawrzynek to give details about practical implementation of the RTP-MIDI protocol, especially the journaling mechanism.Implementation Guide for RTP MIDI. RFC 4696
RFC 4695 has been obsoleted by RFC 6295 in 2011. The protocol has not changed between the two version of the RFC documents, the last one contains correction of errors found in RFC 4695)RTP Payload format for MIDI - RFC 6295
The MMA (MIDI Manufacturers Association) has created a page on its website in order to provide basic information related to RTP-MIDI protocol.https://www.midi.org/midi-articles/rtp-midi-or-midi-over-networks 'About RTP-MIDI' page on MMA website
AppleMIDI Apple Computer introduced RTP-MIDI as a part of their operating system, Mac OS X v10.4, in 2005. The RTP-MIDI driver is reached using the Network icon in the MIDI/Audio Configuration tool. Apple's implementation strictly follows the RFC 4695 for RTP payload and journalling system, but uses a dedicated session management protocol; they do not follow the RFC 4695 session management proposal. This protocol is displayed in Wireshark as "AppleMIDI" and was later documented by Apple.
Apple also created a dedicated class in their mDNS/Bonjour implementation. Devices which comply with this class appear automatically in Apple's RTP-MIDI configuration panel as the Participants directory, making the Apple MIDI system fully 'Plug & Play'. However, it is possible to manually enter IP addresses and ports in this directory to connect to devices which do not support Bonjour.
Apple also introduced RTP-MIDI support in iOS4, but such devices cannot be session initiators.
The RTP-MIDI driver from Apple creates virtual MIDI ports named "Sessions", which are available as MIDI ports in any software, such as sequencers or software instruments, using CoreMIDI, where they appear as a pair of MIDI IN / MIDI OUT ports like any other MIDI 1.0 port or USB MIDI port.
Implementations
Embedded devices In 2006, the Dutch company Kiss-Box presented a first embedded implementation of RTP-MIDI, in different products like MIDI or LTC interfaces.Kiss-Box website (hardware devices using RTP-MIDI protocol) These devices comply with AppleMIDI implementation, using the same session management protocol, in order to be compatible with the other devices and operating system using this protocol.
A proprietary driver was initially developed by the company for Windows XP, but it was restricted to communication with their devices; it was not possible to connect a PC with a Mac computer using this driver. The support of this driver was dropped in 2012 in favor of the standard approach when rtpMIDI driver for Windows became available.
Kiss-Box announced released in 2012 a new generation of CPU boards, named "V3", which support the session initiator functionalities. These models are able to establish sessions with other RTP-MIDI devices without requiring a computer as a control point.
During NAMM 2013, the Canadian company iConnectivity presented a new interface named iConnectivityMIDI4+ which supports RTP-MIDI and allows direct bridging between USB and RTP-MIDI devices. They have since followed up with several other RTP-MIDI capable interfaces, including the mio4 and mio10, and the PlayAUDIO 12.
Windows Tobias Erichsen in 2010 released a Windows implementation of Apple's RTP-MIDI driver.RTP-MIDI driver for Windows This driver works under XP, Vista, Windows 7, Windows 8, and Windows 10, 32 and 64 bit versions. The driver uses a configuration panel very similar to the Apple's one, and is fully compliant with Apple's implementation. It can then be used to connect a Windows machine with a Macintosh computer, but also embedded systems. As with Apple's driver, the Windows driver creates virtual MIDI ports, which become visible from any MIDI application running on the PC. Access is done through mmsystem layer, like all other MIDI ports.
Linux RTP-MIDI support for Linux has been reactivated in February 2013 after an idle period. Availability of drivers have been announced on some forums, based on the original work of Nicolas Falquet and Dominique Fober.
A specific (but incomplete) implementation for Raspberry PI computer is also available, called raveloxmidi.https://github.com/ravelox/pimidi RTP-MIDI implementation dedicated to Raspberry PI platform Check rtpmidid later below for a full implementation.
A full implementation of RTP-MIDI (including the journalling system) is available within the Ubuntu distribution, in the Scenic software package.http://manpages.ubuntu.com/manpages/oneiric/man1/midistream.1.html#contenttoc0 User's manual of RTP-MIDI object called "midistream" under Linux Ubuntu
There is a new implementation, rtpmidid,https://github.com/davidmoreno/rtpmidid rtpmidid at github that integrates seamlessly with the ALSA sequencer, allowing use of tools like QjackCtl to control the connections. This implementation is also available for ARM64, which means it works on Raspberry PI computer.
iOS Apple added full CoreMIDI support in their iOS devices in 2010, allowing the development of MIDI applications for iPhone, iPad and iPods. MIDI then became available from the docking port in the form of a USB controller, allowing connection of USB MIDI devices using the "Apple Camera Kit". It was also available in form of an RTP-MIDI session listener over WiFi.
iOS devices do not support session initiation functionalities, which requires the use of an external session initiator on the network to open an RTP-MIDI session with the iPad. This session initiator can be a Mac computer or a Windows computer with the RTP-MIDI driver activated, or an embedded RTP-MIDI device. The RTP-MIDI session appears under the name "Network MIDI" to all CoreMIDI applications on iOS, and no specific development is required to add RTP-MIDI support in the iOS application. The MIDI port is virtualized by CoreMIDI, so the programmer just needs to open a MIDI connection, regardless of whether the port is connected to USB or RTP-MIDI.
Some complaints arose about the use of the MIDI over USB with iOS devices, since the iPad/iPhone must provide power supply to the external device. Some USB MIDI adapters draw too much current for the iPad, which limits the current and blocks the startup of the device, which then does not appear as available to the application. This problem is avoided by the use of RTP-MIDI.
Javascript Since June 2013, a JavaScript implementation of RTP-MIDI, created by J.Dachtera, is available as an open-source project. The source code is based on Apple's session management protocol, and can act as a session initiator and session listener.
Java Cross-platform Java implementations of RTP-MIDI are possible, particularly 'nmj' library.
WinRT The WinRTP-MIDI project http://winrtpmidi.codeplex.com Website of open-source WinRTP-MIDI project is an open-source implementation of RTP-MIDI protocol stack under Windows RT. The code was initially designed to be portable between the various versions of Windows, but the last version has been optimized for WinRT, in order to simplify the design of applications for Windows Store.
Arduino RTP-MIDI was available for the Arduino platform in November 2013, under the name "AppleMIDI library".RTP-MIDI/AppleMIDI library for Arduino The software module can run either on Arduino modules with integrated Ethernet adapter, like the Intel Galileo, or run on the "Ethernet shield".
KissBox produces an RTP-MIDI OEM module, an external communication processor board, which connects over an SPI bus link.
MIDIbox In December 2013, two members of the MIDIbox DIY group started to work on an initial version of MIOS (MIDIbox Operating System) including RTP-MIDI support over a fast SPI link. In order to simplify integration, it was decided to use an external network processor board handling the whole protocol stack. A first beta version was released in the second week of January 2014.MIDIbox forum announcement of RTP-MIDI support in MIOS The first official software was released during first week of March 2014.
The protocol used on the SPI link between the MIOS processor and the network processor is based on the same format as USB, using 32-bit words containing a complete MIDI message, and has been proposed as an open standard for communication between network processor modules and MIDI application boards.
Axoloti The Axoloti is an open-source hardware synthesizer based on a STM32F427 ARM processor. This synthesizer is fully programmable using a virtual patch concept, similar to Max/MSP, and includes a full MIDI support. A node.js extension has been developed to allow RTP-MIDI connection of an Axoloti with any RTP-MIDI devices.https://gist.github.com/DatanoiseTV/6a59fc66517fbd923ed9 Node.js extension to provide RTP-MIDI connection to Axoloti The Axoloti hardware can also be equipped with a RTP-MIDI external coprocessor, connected via the SPI bus available on the expansion port of the Axoloti core. The approach is the same as the one described for Arduino and MIDIbox.
MIDIKit Cross-platform library MIDIKit is an open-source, cross-platform library which provides a unified MIDI API for the various MIDI API available on the market (Core MIDI, Windows MME, Linux ALSA, etc...). MIDIKit supports RTP-MIDI protocol, including the journalling system. RTP-MIDI ports are seen within MIDIKit as complementary ports (they do not rely on rtpMIDI driver), added to native system MIDI portshttps://github.com/jpommerening/midikit/blob/master/driver/common/rtpmidi.c Cross-platform unified MIDI library with integrated RTP-MIDI support
Driverless use Since RTP-MIDI is based on UDP/IP, any application can implement the protocol directly, without needing any driver. The drivers are needed only when users want to make the networked MIDI ports appear as a standard MIDI port. For example, some Max/MSP objects and VST plugins have been developed following this methodology.
RTP-MIDI over AVB AVB is a set of technical standards which define specifications for extremely low latency streaming services over Ethernet networks. AVB networks are able to provide latencies down to one audio sample across a complete network. RTP-MIDI is natively compatible with AVB networks, like any other IP protocol, since AVB switches (also known as "IEEE802.1 switches") automatically manage the priority between real-time audio/video streams and IP traffic. RTP-MIDI protocol can also use the real-time capabilities of AVB if the device implements the RTCP payload described in IEEE-1733 document.IEEE Standard for Layer 3 Transport Protocol for Time-Sensitive Applications in Local Area Networks RTP-MIDI applications can then correlate the "presentation" timestamp, provided by IEEE-802.1 Master Clock, with the RTP timestamp, ensuring a sample-accurate time distribution of the MIDI events.
Protocol