yabridge

Yet Another way to use Windows VST2 plugins in Linux VST hosts.

TODOs

There are a few things that should be done before making this public, including:

Document and improve the installation and updating procedure.
Finish documenting the project setup and the way communication works. In particular we're missing the wait void pointers in the event dispatchers are handled and how the AEffect struct gets synchronized. I should probably also rewrite some parts of it to make it clearer.
Document what this has been tested on and what does or does not work.
Document wine32 support.
Forward updates from the Windows VST plugin's AEffect struct, if that's a thing.
Fix processReplacing forwarding.
Implement GUIs.
Chunks. For effSetChunk we can now just use the strings. For effGetChunk we need to find a clean way to 1. make the returned string exactly n bytes long, where n is the value returned by the VST plugin's dispatch() function (could be an option for WritableBuffer), and 2. store the returned data in a std::vector<uint8_t> on the HostBridge struct and write back a pointer to that instead. That might involve extending DefaultDataConverter to also handle writing back values.
Check if we need special handling for the effGetChunk and effSetChunk events.
Mention precompiled binaries and building from source in the installation section.
Add proper debugging support activated using an environment variable.
- Write all stdout and stderr output from the plugin to a temporary file so it can be inspected when using a host such as Bitwig that hides this by default.
- Catch exceptions during initialization and print them to stderr.

Usage

There are two ways to use yabridge.

Symlinking (recommended)

The recommended way to use yabridge is through symbolic links. This allows you to update yabridge for all of your plugins in one go, and it also avoids having to install it globally.

You can either use the precompiled binaries from the GitHub releases section, or you could build yabridge directly from source. If you use the precompiled binaries, then simply extract them to ~/.local/share/yabridge or any other place in your home directory. If you choose to build from source, then you can directly use the binaries from the build/ directory. For the section below I'm going to assume you've placed the files in ~/.local/share/yabridge.

To set up yabridge for a VST plugin called ~/.wine/drive_c/Program Files/Steinberg/VstPlugins/plugin.dll, simply create a symlink from ~/.local/share/yabridge/libyabridge.so to ~/.wine/drive_c/Program Files/Steinberg/VstPlugins/plugin.so like so:

ln -s ~/.local/share/yabridge/libyabridge.so "$HOME/.wine/drive_c/Program Files/Steinberg/VstPlugins/plugin.so"

For instance, if you wanted to set up yabridge for any of the VST plugins under ~/.wine/drive_c/Program Files/Steinberg/VstPlugins, you could do something like this:

find "$HOME/.wine/drive_c/Program Files/Steinberg/VstPlugins" -type f -iname '*.dll' -print0 \
  | sed -z 's/\.dll$/.so/' \
  | xargs -0 -n1 ln -sf ~/.local/share/yabridge/libyabridge.so

Copying

It's also possible to use yabridge by making copies of libyabridge.so instead of creating symlinks. This is not recommended as it makes updating a hassle. If you choose to do this, then you'll have to make sure yabridge-host.exe and yabridge-host.exe.so are somewhere in your search path as otherwise yabridge won't know where to find them. Either copy them to /usr/local/bin (not recommended) or to ~/.local/bin and make sure that the directory is in your PATH environment variable.

Building

To compile yabridge, you'll need Meson and the following dependencies:

gcc (tested using GCC 9.2)
A Wine installation with wiengcc and the development headers.
Boost

The following dependencies are included as a Meson wrap:

bitsery

The project can then be compiled as follows:

meson setup --buildtype=release --cross-file cross-wine64.conf build
ninja -C build

When developing or debugging yabridge you can change the build type to either debug or debugoptimized to enable debug symbols and optionally also disable optimizations.

Debugging

Wine's error messages and warning are typically very helpful whenever a plugin doesn't work right away. Sadly this information is not always available. For instance Bitwig hides a plugin's STDOUT and STDERR streams from you. To make it easier to debug malfunctioning plugins, yabridge offers two environment variables:

YABRIDGE_DEBUG_FILE=<path> allows you to write the Wine VST host's STDOUT and STDERR messages to a file. For example, you could launch your DAW with env YABRIDGE_DEBUG_FILE=/tmp/yabridge.log <daw>, and then use tail -F /tmp/yabridge.log to keep track of that file. If this option is not absent then yabridge will write its debug messages to STDERR instead.
YABRIDGE_DEBUG_LEVEL={0,1} allows you to set the verbosity of the debug information. Every level increases the verbosity of the debug information:
- A value of 0 (the default) means that yabridge will only output messages from the Wine process and some basic information such as the plugin being loaded and the wineprefix being used.
- A value of 1 will log information about all events and function calls being sent between the VST host and the plugin. This can be very verbose but it makes it easier to see if yabridge is handling things incorrectly.
More detailed information about these levels can be found in src/common/logging.h.

Rationale

I started this project because the alternatives were either unmaintained, not self-contained or very difficult to work with. With this implementation I'd like to prioritize maintainability and correctness, even if it would cause slightly more overhead than a more optimized solution would. Please let me know if you have any suggestions on how to improve this!

Architecture

The project consists of two components, a Linux native VST plugin (libyabridge.so) and a VST host that runs under Wine (yabridge-host.exe/yabridge-host.exe.so). I'll refer to a copy or symlink of libyabridge.so as the plugin, the native Linux VST host that's hosting the plugin as the native VST host, the Wine VST host that's hosting a Windows .dll file as the Wine VST host, and the Windows VST plugin that's loaded in the Wine VST host is simply the Windows VST plugin. The whole process works as follows:

Some copy of or a symlink to libyabridge.so gets loaded as a VST plugin in a Linux VST host. This file should have been renamed to match a Windows VST plugin .dll file in the same directory. For instance, if there's a Serum_x64.dll file you'd like to bridge, then libyabridge.so should be renamed to Serum_x64.so.
The plugin first attempts to locate:
- The location of yabridge-host.exe. For this it will first search for the file either alongside plugin. This is useful for development, as it allows you to use a symlink to libyabridge.so from the build directory causing yabridge to use the corresponding yabridge-host.exe from the same build directory. If this file can't be found, it will fall back to searching through the search path.
- The wine prefix plugin is located in
- The corresponding Windows VST plugin .dll file.
The plugin then sets up a Unix domain socket endpoint to communicate with the Wine VST host somewhere in a temporary directory. I chose to use Unix domain sockets rather than shared memory to avoid having to do manual synchronization and because they have very low overhead. Since the Wine VST host can't access the Linux VST host's memory we would have to copy audio buffers in either case.
The plugin launches the Wine VST host in the detected wine prefix, passing the name of the .dll file it should be loading and the path to the Unix domain socket that was just created.
Communication gets set up using multiple sockets over the same end point. This allows us to use blocking read operations while handling a certain event type to avoid receiving messages out of order. The following types of events get assigned a socket:
- Calls from the native VST host to the plugin's dispatch() function. These get forwarded to the Windows VST plugin through the Wine VST host.
- Host callback calls from the Windows VST plugin loaded into the Wine VST host through the audioMasterCallback function. These get forwarded to the native VST host through the plugin.
- Calls from the native VST host to the plugin's getParameter() and setParameter() functions. Both functions get forwarded to the Windows VST plugin through the Wine VST host using a single socket.
- Calls from the native VST host to the plugin's process() and processReplacing() functions. Both functions get forwarded to the Windows VST plugin through the Wine VST host using a single socket.
The first step when passing through any of these function calls over a socket is to serialize the function's parameters as binary data. Both request and the corresponding response objects for all of these function calls can be found in src/common/communication.h, along with functions to read and write these objects over streams and sockets. The actual binary serialization is handled using bitsery.
The Wine VST host loads the Windows VST plugin and starts forwarding messages over the sockets described above.
After the Windows VST plugin has started loading we will forward all values from the plugin's AEffect struct to the Linux native VST plugin. After this point the plugin will stop blocking and has finished loading.

TODO: Do plugins update their AEffect struct update itself after initialization? For instance to change the number of parameters. Is there any way to catch this other than checking for updates ourselves?

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