How to Make a Plugin

Introduction

At this time, Shotcut only supports Filter plugins. However, in the mid-term future we hope to offer transitions and generators. There are two parts to a plugin: the backend that does the actual audio or video processing and the front-end that offers a user interface (UI). By design, there is no support to automatically generate a UI for the parameters of your plugin. Neither is it possible to launch an external, platform-native UI as many tools do.

Backend

You can make a new backend using a number of technologies including MLT, frei0r, LADSPA, or WebVfx. There are also many existing plugins for these that are already bundled with Shotcut builds that do not yet have a frontend! Thus, you might want to use an existing MLT filter and simply create a frontend for it. Continue reading for more information about creating a new backend.

Audio

You can make a MLT or LADSPA plugin. Both of these require C or C++ coding. MLT support the following sample formats:

  • signed 16-bit interleaved PCM
  • signed 32-bit non-interleaved PCM
  • signed 32-bit interleaved PCM
  • 32-bit non-interleaved floating point
  • 32-bit interleaved floating point
  • unsigned 8-bit interleaved PCM

LADSPA supports only 32-bit non-interleaved floating point.

Video

You make a MLT, frei0r, or WebVfx plugin. MLT and frei0r plugins require C or C++ coding; whereas WebVfx lets you use HTML5, CSS3, JavaScript, SVG, and WebGL.

MLT supports the following pixel formats:

  • YUV 4:2:2, 8-bits per component, packed, in Rec. 601 or 709 colorspaces; along with an optional, separate 8-bit alpha channel bitmap.
  • RGB or RGBA, 8-bits per component, packed, in sRGB colorspace.

frei0r and WebVfx only supports 8-bit RGB(A).

Frontend

The frontend is implemented using Qt 5 QML/Quick. You can also use Quick Controls, and Shotcut offers some custom controls as well.

First, you must create a folder to contain your QML. Your folder must be copied to the share/shotcut/qml/filters to install it.

Next, you need to create a filter metadata QML file that must begin with “meta” and end with “.qml”. This QML must include QtQuick and org.shotcut.qml and create a Metadata object at the top level. Here is an example:

import QtQuick 2.0
import org.shotcut.qml 1.0

Metadata {
    type: Metadata.Filter
    name: qsTr("Alpha Channel: Adjust")
    mlt_service: 'frei0r.alpha0ps'
    objectName: 'alphaChannelAdjust'
    qml: 'ui.qml'
}

Finally, you can create the QML files for the panel and the VUI (video user interface), which is a UI that appears atop the video player region. There is still much to document to help create frontends, but we suggest you look at the code in your Shotcut installation to learn for now.

Here are all of the Metadata properties available:

Name Type Description
type PluginType Metadata.Filter (required)
name string The name as it appears to the user. Use qsTr() to make it translatable. (required)
mlt_service string This is the MLT service (plugin) identifier. (required)
objectName string This is the name that gets put into XML project file in case there may be more than one Shotcut filter for the same MLT service. It is optional but strongly advised especially if using MLT open source services.
needsGPU bool Wether this filter requires GPU processing - only available for Shotcut’s branch of Movit. (default false)
qml string The relative file name of the UI QML for the filter panel.
vui string The relative file name of the UI QML for the video preview.
isAudio bool True if this is an audio plugin, otherwise video. (default false)
isHidden bool True to make this hidden from the filter menu. This is useful to keep a legacy frontend for existing projects but make a new implementation for new projects. (default false)
isFavorite bool True to make it appear in the favorites menu by default. (default false)
gpuAlt string Prevent a CPU-based filter from appearing when GPU processing is enabled by setting this to the name (mlt_service if not objectName) of the GPU alternative for this filter.
allowMultiple bool False to prevent the user from adding this filter more than once to a selected clip or track. (default true)
isClipOnly bool True to prevent the user from adding the filter to a track or the timeline. (default false)

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Shotcut is a free, open source, cross-platform video editor for Windows, Mac and Linux. Major features include support for a wide range of formats; no import required meaning native timeline editing; Blackmagic Design support for input and preview monitoring; and resolution support to 4k.

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