A command-line VST plugin host
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MrsWatson is a command-line audio plugin host. It takes an audio and/or MIDI file as input, and processes it through one or more VST plugins. MrsWatson was designed primarily for two purposes:

  • Audio plugin development and testing
  • Automated audio processing tasks

Say you have an audio file which you would like to process with an effect plugin.

mrswatson --input mysong.wav --output out.wav --plugin myplugin

This will run mysong.wav through the myplugin VST, placing the processed output in out.wav, as well as logging some output to the console:

- 00000000 000000 MrsWatson version 0.9.7 initialized, build 20150112
- 00000000 000000 Setting 2 channels
- 00000000 000000 Setting sample rate to 44100Hz
- 00000000 000000 Plugin 'myplugin.vst' is of type VST2.x
- 00000000 000000 Opening VST2.x plugin 'myplugin.vst'
- 00000000 000001 Starting processing input source
- 00010752 000002 Total processing time 1ms, approximate breakdown:
- 00010752 000002   MrsWatson Initialization: 1ms (69.4%)
- 00010752 000002   MrsWatson Input Source: 0ms (12.4%)
- 00010752 000002   MrsWatson Output Source: 0ms (11.6%)
- 00010752 000002   myplugin.vst Audio Processing: 0ms (3.9%)
- 00010752 000002   myplugin.vst MIDI Processing: 0ms (0.0%)
- 00010752 000002 Read 10595 frames from mysong.wav
- 00010752 000002 Wrote 10752 frames to out.wav
- 00010752 000002 Shutting down
- 00010752 000002 Closing plugin 'myplugin.vst'
- 00010752 000002 Goodbye!

To see more or less logging output, use the --verbose or --quiet options, respectively. MrsWatson generates colored output (if your terminal supports it) with two times per line, the first for the current sample and the second for the time in milliseconds since processing began. The sample time also changes colors after every 44100 samples to help visually break up processing times.

To process a MIDI file through an instrument using an FXP preset to be loaded into the VST, you'd do something like this:

mrswatson --midi-file mysong.mid --output out.wav --plugin piano,soft.fxp

Like the first example, a list of plugins separated with semi-colons can be given here so that the audio generated by the instrument can be processed through any number of effects. Note that you might have to escape characters like semi-colons from your shell.

Complete help for MrsWatson can be found by running the program with no arguments, or with --help. To see extended help for all options (which prints quite a lot of output) run mrswatson --help full.

Loading Plugins

Currently, MrsWatson loads plugins by their short name by searching in the standard installation locations for your platform, as well as the current working directory and by absolute path. Use the --list-plugins option to see the order of locations searched and the plugins found there.

MrsWatson supports setting plugin parameters with the --parameter switch. However, if you would like to set many parameters on a plugin, it may be more efficient to create an FXP preset and load it with the plugin. For information on presets, run mrswatson --help plugin.

64-Bit Support

MrsWatson supports both 32-bit and 64-bit plugins, but not from the same executable. Two executables are shipped in the distribution zipfile for each platform, mrswatson and mrswatson64, which are the 32-bit and 64-bit variants, respectively. Each one is only able to process with plugins of the same architecture. Running either executable with the --list-plugins switch will print out all supported plugins that the program is compatible with.

Although on Mac OS X, a single Universal Binary could theoretically be used to suport both architectures, Darwin prefers to launch the one which matches the system architecture, which thus makes it impossible to load 32-bit plugins on a 64-bit system. For this reason (and also to be consistent with other platforms) Universal Binaries are not used on Mac OS X.

Bug Reporting

If you believe you have found a bug in MrsWatson, please try first running it with the --verbose argument. This will generate extra logging output which may help to solve the problem.

The easiest way to report a bug is to send an email to Teragon Audio's support address: support (at) teragonaudio (dot) com. MrsWatson has a special command-line switch to aid in diagnosing runtime problems, --error-report. When enabled it will create a zipfile on the desktop containing the input, output, logs, and optionally the plugins themselves. Please include these reports for bugs resulting in incorrect behavior or crashes.

A test suite program, named mrswatsontest, can be found in the Mrswatson zipfile. If tests fail on your platform, please report this along with your bug. Please note that there is also a 64-bit version, mrswatsontest64.

MrsWatson uses GitHub issues for bug reporting, if you would like to submit an issue yourself.


Instructions for building MrsWatson can be found in the file BUILDING.md.


If you are using MrsWatson to do something cool, please send me a link to your project! If you appreciate MrsWatson and would like to donate money, please instead make a donation to a charity on our behalf, and let us know about it. The organizations which have helped us the most are:

  • EFF: Without the EFF, programs like MrsWatson would be significantly harder to create and distribute.
  • Wikipedia: Writing MrsWatson involves a lot of research as well as coding, and Wikipedia is an essential part of this.

Special Thanks

Big additional thanks to:

  • Andrew McCrea, (@thrusong)
  • Michael Pruett, (@mpruett)
  • Jarl Friis (@jarl-dk)


MrsWatson is made available under the BSD license. For more details, see the LICENSE.txt file distributed with the source code. MrsWatson also uses the following third-party libraries, which are licensed under the respective agreements:

  • VST: Licensed under Steinberg's VST SDK license agreement, version 2.4. For more information, see Steinberg's developer portal.
  • libaudiofile: Written by Michael Pruett, licensed under GNU Library General Public License.