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jacket

A Nim wrapper for the JACK client side C API aka libjack.

Project status

This software is in beta status.

The majority of JACK client APIs have been wrapped and are functional (see examples), but some APIs (e.g. threading) still need wrapping. Others, like the server control or the deprecated session API, will probably not be covered by these bindings. While this project is in beta stage, symbol names may still be changed and things moved around before the first stable release.

Installation

Clone this repository.
Change into the jacket directory.
Run nimble install (or nimble develop).
Run the examples with nim compile --run examples/<example>.nim.

(Some examples need --threads:on with Nim < 2.0).

Usage

Here is a very minimal JACK client application, which just passes audio through from its single input port to its output port.

Any error checking and handling has been omitted for brevity's sake. See the files in the examples directory for more robust example code.

import std/os
import system/ansi_c
import jacket

var
    jackClient: ClientP
    status: cint
    exitSignalled: bool = false
    inpPort, outPort: PortP
type JackBufferP = ptr UncheckedArray[DefaultAudioSample]

proc signalCb(sig: cint) {.noconv.} =
    exitSignalled = true

proc shutdownCb(arg: pointer = nil) {.cdecl.} =
    exitSignalled = true

proc processCb(nFrames: NFrames, arg: pointer): cint {.cdecl.} =
    var inpbuf = cast[JackBufferP](portGetBuffer(inpPort, nFrames))
    var outbuf = cast[JackBufferP](portGetBuffer(outPort, nFrames))
    # copy samples from input to output buffer
    for i in 0 ..< nFrames:
        outbuf[i] = inpbuf[i]

# Create JACK Client ptr
jackClient = clientOpen("passthru", NullOption, status.addr)
# Register audio input and output ports
inpPort = jackClient.portRegister("in_1", JACK_DEFAULT_AUDIO_TYPE, PortIsInput, 0)
outPort = jackClient.portRegister("out_1", JACK_DEFAULT_AUDIO_TYPE, PortIsOutput, 0)
# Set JACK callbacks
jackClient.onShutdown(shutdownCb)
discard jackClient.setProcessCallback(processCb, nil)
# Handle POSIX signals
c_signal(SIGINT, signalCb)
c_signal(SIGTERM, signalCb)
# Activate JACK client ...
discard jackClient.activate()

while not exitSignalled:
    sleep(50)

discard jackClient.clientClose()

License

This software is released under the MIT License. See the file LICENSE.md for more information.

Please note that the JACK client library (libjack), which this project wraps, is licensed under the LGPL-2.1. This wrapper does not statically or dynamically link to libjack, but only loads it via the dynamic linker at run-time.

Software using this wrapper is, in the opinion of its author, not considered a derivative work of libjack and not required to be released under the LGPL, but no guarantees are made in this regard and users are advised to employ professional legal counsel when in doubt.

Author

jacket is written by Christopher Arndt.