PortAudio wrapper for the Julia programming language, compatible with the JuliaAudio family of packages



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PortAudio.jl is a wrapper for libportaudio, which gives cross-platform access to audio devices. It is compatible with the types defined in SampledSignals.jl. It provides a PortAudioStream type, which can be read from and written to.

Opening a stream

The easiest way to open a source or sink is with the default PortAudioStream() constructor, which will open a 2-in, 2-out stream to your system's default device(s). The constructor can also take the input and output channel counts as positional arguments, or a variety of other keyword arguments.

PortAudioStream(inchans=2, outchans=2; eltype=Float32, samplerate=48000Hz, latency=0.1, synced=false)

You can open a specific device by adding it as the first argument, either as a PortAudioDevice instance or by name. You can also give separate names or devices if you want different input and output devices

PortAudioStream(device::PortAudioDevice, args...; kwargs...)
PortAudioStream(devname::AbstractString, args...; kwargs...)

You can get a list of your system's devices with the PortAudio.devices() function:

julia> PortAudio.devices()
6-element Array{PortAudio.PortAudioDevice,1}:
 PortAudio.PortAudioDevice("AirPlay","Core Audio",0,2,0)
 PortAudio.PortAudioDevice("Built-in Microph","Core Audio",2,0,1)
 PortAudio.PortAudioDevice("Built-in Output","Core Audio",0,2,2)
 PortAudio.PortAudioDevice("JackRouter","Core Audio",2,2,3)
 PortAudio.PortAudioDevice("After Effects 13.5","Core Audio",0,0,4)
 PortAudio.PortAudioDevice("Built-In Aggregate","Core Audio",2,2,5)

Input/Output Synchronization

The synced keyword argument to PortAudioStream controls whether the input and output ringbuffers are kept synchronized or not, which only effects duplex streams. It should be set to true if you need consistent input-to-output latency. In a synchronized stream, the underlying PortAudio callback will only read and write to the buffers an equal number of frames. In a synchronized stream, the user must also read and write an equal number of frames to the stream. If it is only written to or read from, it will eventually block. This is why it is false by default.

Reading and Writing

The PortAudioStream type has source and sink fields which are of type PortAudioSource <: SampleSource and PortAudioSink <: SampleSink, respectively. are subtypes of SampleSource and SampleSink, respectively (from SampledSignals.jl). This means they support all the stream and buffer features defined there. For example, if you load SampledSignals with using SampledSignals you can read 5 seconds to a buffer with buf = read(stream.source, 5s), regardless of the sample rate of the device.

PortAudio.jl also provides convenience wrappers around the PortAudioStream type so you can read and write to it directly, e.g. write(stream, stream) will set up a loopback that will read from the input and play it back on the output.


Set up an audio pass-through from microphone to speaker

stream = PortAudioStream(2, 2)
    # cancel with Ctrl-C
    write(stream, stream)

Use do syntax to auto-close the stream

PortAudioStream(2, 2) do stream
    write(stream, stream)

Open your built-in microphone and speaker by name

PortAudioStream("Built-in Microph", "Built-in Output") do stream
    write(stream, stream)

Record 10 seconds of audio and save to an ogg file

julia> using PortAudio, SampledSignals, LibSndFile

julia> stream = PortAudioStream("Built-in Microph", 2, 0)
  Samplerate: 48000 s⁻¹
  Buffer Size: 4096 frames
  2 channel source: "Built-in Microph"

julia> buf = read(stream, 10s)
480000-frame, 2-channel SampleBuf{Float32, 2, SIUnits.SIQuantity{Int64,0,0,-1,0,0,0,0,0,0}}
10.0 s at 48000 s⁻¹

julia> close(stream)

julia> save(joinpath(homedir(), "Desktop", "myvoice.ogg"), buf)

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