CPAL - Cross-Platform Audio Library
Low-level library for audio input and output in pure Rust.
This library currently supports the following:
- Enumerate supported audio hosts.
- Enumerate all available audio devices.
- Get the current default input and output devices.
- Enumerate known supported input and output stream formats for a device.
- Get the current default input and output stream formats for a device.
- Build and run input and output PCM streams on a chosen device with a given stream format.
Currently supported hosts include:
- Linux (via ALSA)
- Windows (via WASAPI by default, see ASIO instructions below)
- macOS (via CoreAudio)
- iOS (via CoreAudio)
- Emscripten
Note that on Linux, the ALSA development files are required. These are provided
as part of the libasound2-dev
package on Debian and Ubuntu distributions and
alsa-lib-devel
on Fedora.
ASIO on Windows
ASIO is an audio driver protocol by Steinberg. While it is available on multiple operating systems, it is most commonly used on Windows to work around limitations of WASAPI including access to large numbers of channels and lower-latency audio processing.
CPAL allows for using the ASIO SDK as the audio host on Windows instead of WASAPI. To do so, follow these steps:
-
Download the ASIO SDK
.zip
from this link. The version as of writing this is 2.3.1. -
Extract the files and place the directory somewhere you are happy for it to stay (e.g.
~/.asio
). -
Assign the full path of the directory (that contains the
readme
,changes
,ASIO SDK 2.3
pdf, etc) to theCPAL_ASIO_DIR
environment variable. This is necessary for theasio-sys
build script to build and bind to the SDK. -
bindgen
, the library used to generate bindings to the C++ SDK, requires clang. Download and install LLVM from here under the "Pre-Built Binaries" section. The version as of writing this is 7.0.0. -
Add the LLVM
bin
directory to aLIBCLANG_PATH
environment variable. If you installed LLVM to the default directory, this should work in the command prompt:setx LIBCLANG_PATH "C:\Program Files\LLVM\bin"
-
If you don't have any ASIO devices or drivers available, you can download and install ASIO4ALL. Be sure to enable the "offline" feature during installation despite what the installer says about it being useless.
-
Loading VCVARS.
rust-bindgen
uses the C++ tool-chain when generating bindings to the ASIO SDK. As a result, it is necessary to load some environment variables in the command prompt that we use to build our project. On 64-bit machines run:"C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" amd64
On 32-bit machines run:
"C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x86
Note that, depending on your version of Visual Studio, this script might be in a slightly different location.
-
Select the ASIO host at the start of our program with the following code:
let host; #[cfg(target_os = "windows")] { host = cpal::host_from_id(cpal::HostId::Asio).expect("failed to initialise ASIO host"); }
If you run into compilations errors produced by
asio-sys
orbindgen
, make sure thatCPAL_ASIO_DIR
is set correctly and trycargo clean
. -
Make sure to enable the
asio
feature when building CPAL:cargo build --features "asio"
or if you are using CPAL as a dependency in a downstream project, enable the feature like this:
cpal = { version = "*", features = ["asio"] }
In the future we would like to work on automating this process to make it easier, but we are not familiar enough with the ASIO license to do so yet.
Updated as of ASIO version 2.3.3.