audio-processor-standalone-midi

Wraps midir to provide MIDI input handling. The host may be started with MidiHost.

When MIDI messages are received, they're pushed onto a lock-free atomic_queue::Queue. The messages are picked-up in the audio-thread by MidiAudioThreadHandler.

It provides easy stand-alone MIDI integration with:

• audio-processor-traits - MidiEventHandler trait
• rust-vst - PluginInstance

This crate provides conversion into the VST types, which is to allow a VST host to use it. This is provided by the MidiVSTConverter.

Currently, MIDI messages over 3 bytes are dropped by this host. In addition, the queue is bounded & a size must be provided. Default implementations will use a MIDI queue capacity of 100.

Memory Safety

In order to integrate with the VST C API, this crate does manual memory allocation and handling. This is due to VST event types being unrepresentable as safe Rust constructs (and due to real-time safety being required as well).

Real-time Safety

This crate provides the host side, which is the MIDI host. This host allocates when it receives messages from midir.

The events are forwarded onto a lock-free queue (atomic_queue).

On the audio_thread and vst modules, past construction methods that should be called on the audio-thread will not (de)-allocate. This is tested using the assert_no_alloc crate.

In addition, basedrop / audio_garbage_collector are used to prevent de-allocation from happening on the audio-thread.

Test coverage

The crate has unit-tests (though it should be considered experimental as all of this repository).

Test coverage is at 80%.

Actix & Actors

The MidiHost exposes an actix API, to be used with the actix actor system. This is to ease communicating with the midi handler from multiple threads.